capsules_core/

process_console.rs

// Licensed under the Apache License, Version 2.0 or the MIT License.
// SPDX-License-Identifier: Apache-2.0 OR MIT
// Copyright Tock Contributors 2022.

//! Implements a text console over the UART that allows
//! a terminal to inspect and control userspace processes.
//!
//! For a more in-depth documentation check /doc/Process_Console.md
use core::cell::Cell;
use core::cmp;
use core::fmt;
use core::fmt::write;
use core::str;
use kernel::capabilities::ProcessManagementCapability;
use kernel::capabilities::ProcessStartCapability;
use kernel::hil::time::ConvertTicks;
use kernel::utilities::cells::MapCell;
use kernel::utilities::cells::TakeCell;
use kernel::ProcessId;

use kernel::debug;
use kernel::hil::time::{Alarm, AlarmClient};
use kernel::hil::uart;
use kernel::introspection::KernelInfo;
use kernel::process::{ProcessPrinter, ProcessPrinterContext, State};
use kernel::utilities::binary_write::BinaryWrite;
use kernel::ErrorCode;
use kernel::Kernel;

/// Buffer to hold outgoing data that is passed to the UART hardware.
pub const WRITE_BUF_LEN: usize = 500;
/// Buffer responses are initially held in until copied to the TX buffer and
/// transmitted.
pub const QUEUE_BUF_LEN: usize = 300;
/// Since reads are byte-by-byte, to properly echo what's typed,
/// we can use a very small read buffer.
pub const READ_BUF_LEN: usize = 4;
/// Commands can be up to 32 bytes long: since commands themselves are 4-5
/// characters, limiting arguments to 25 bytes or so seems fine for now.
pub const COMMAND_BUF_LEN: usize = 64;
/// Default size for the history command.
pub const DEFAULT_COMMAND_HISTORY_LEN: usize = 10;

/// List of valid commands for printing help. Consolidated as these are
/// displayed in a few different cases.
const VALID_COMMANDS_STR: &[u8] =
    b"help status list stop start fault boot terminate process kernel reset panic console-start console-stop\r\n";

/// Escape character for ANSI escape sequences.
const ESC: u8 = b'\x1B';

/// End of line character.
const EOL: u8 = b'\x00';

/// Backspace ANSI character
const BS: u8 = b'\x08';

/// Delete ANSI character
const DEL: u8 = b'\x7F';

/// Space ANSI character
const SPACE: u8 = b'\x20';

/// Carriage return ANSI character
const CR: u8 = b'\x0D';

/// Newline ANSI character
const NLINE: u8 = b'\x0A';

/// Upper limit for ASCII characters
const ASCII_LIMIT: u8 = 128;

/// States used for state machine to allow printing large strings asynchronously
/// across multiple calls. This reduces the size of the buffer needed to print
/// each section of the debug message.
#[derive(PartialEq, Eq, Copy, Clone, Default)]
enum WriterState {
    #[default]
    Empty,
    KernelStart,
    KernelBss,
    KernelInit,
    KernelStack,
    KernelRoData,
    KernelText,
    ProcessPrint {
        process_id: ProcessId,
        context: Option<ProcessPrinterContext>,
    },
    List {
        index: isize,
        total: isize,
    },
}

/// Key that can be part from an escape sequence.
#[derive(Copy, Clone)]
enum EscKey {
    Up,
    Down,
    Left,
    Right,
    Home,
    End,
    Delete,
}

/// Escape state machine to check if
/// an escape sequence has occured
#[derive(Copy, Clone)]
enum EscState {
    /// This state is reached when the character is a normal
    /// ANSI character, and the escape sequence is bypassed.
    Bypass,

    /// This state is reached when an escape sequence
    /// is completed, and the corresponding EscKey is processed.
    Complete(EscKey),

    /// This state is reached when an escape sequence has
    /// just started and is waiting for the next
    /// character to complete the sequence.
    Started,

    /// This state is reached when the escape sequence
    /// starts with a bracket character '[' and is waiting
    /// for the next character to determine the corresponding EscKey.
    Bracket,
    Bracket3,

    /// This state is reached when the current character does not match
    /// any of the expected characters in the escape sequence.
    /// Once entered in this state, the escape sequence cannot be processed
    /// and is waiting for an ascii alphabetic character to complete
    /// the unrecognized sequence.
    Unrecognized,

    /// This state is reached when the escape sequence has ended with
    /// an unrecognized character. This state waits for an ascii
    /// alphabetic character to terminate the unrecognized sequence.
    UnrecognizedDone,
}

impl EscState {
    fn next_state(self, data: u8) -> Self {
        use self::{
            EscKey::{Delete, Down, End, Home, Left, Right, Up},
            EscState::{
                Bracket, Bracket3, Bypass, Complete, Started, Unrecognized, UnrecognizedDone,
            },
        };
        match (self, data) {
            (Bypass, ESC) | (UnrecognizedDone, ESC) | (Complete(_), ESC) => Started,
            // This is a short-circuit.
            // ASCII DEL and ANSI Escape Sequence "Delete" should be treated the same way.
            (Bypass, DEL) | (UnrecognizedDone, DEL) | (Complete(_), DEL) => Complete(Delete),
            (Bypass, _) | (UnrecognizedDone, _) | (Complete(_), _) => Bypass,
            (Started, b'[') => Bracket,
            (Bracket, b'A') => Complete(Up),
            (Bracket, b'B') => Complete(Down),
            (Bracket, b'D') => Complete(Left),
            (Bracket, b'C') => Complete(Right),
            (Bracket, b'H') => Complete(Home),
            (Bracket, b'F') => Complete(End),
            (Bracket, b'3') => Bracket3,
            (Bracket3, b'~') => Complete(Delete),
            _ => {
                if EscState::terminator_esc_char(data) {
                    UnrecognizedDone
                } else {
                    Unrecognized
                }
            }
        }
    }

    /// Checks if the escape state machine is in the middle
    /// of an escape sequence
    fn in_progress(&self) -> bool {
        matches!(self, EscState::Bracket) || matches!(self, EscState::Bracket3)
    }

    /// Checks if the escape state machine is at the start
    /// of processing an escape sequence
    fn has_started(&self) -> bool {
        matches!(self, EscState::Started)
    }

    fn terminator_esc_char(data: u8) -> bool {
        data.is_ascii_alphabetic() || data == b'~'
    }
}

/// Data structure to hold addresses about how the kernel is stored in memory on
/// the chip.
///
/// All "end" addresses are the memory addresses immediately following the end
/// of the memory region.
pub struct KernelAddresses {
    pub stack_start: *const u8,
    pub stack_end: *const u8,
    pub text_start: *const u8,
    pub text_end: *const u8,
    pub read_only_data_start: *const u8,
    pub relocations_start: *const u8,
    pub relocations_end: *const u8,
    pub bss_start: *const u8,
    pub bss_end: *const u8,
}

/// Track the operational state of the process console.
#[derive(Clone, Copy, PartialEq)]
enum ProcessConsoleState {
    /// The console has not been started and is not listening for UART commands.
    Off,
    /// The console has been started and is running normally.
    Active,
    /// The console has been started (i.e. it has called receive), but it is not
    /// actively listening to commands or showing the prompt. This mode enables
    /// the console to be installed on a board but to not interfere with a
    /// console-based app.
    Hibernating,
}

pub struct ProcessConsole<
    'a,
    const COMMAND_HISTORY_LEN: usize,
    A: Alarm<'a>,
    C: ProcessManagementCapability + ProcessStartCapability,
> {
    uart: &'a dyn uart::UartData<'a>,
    alarm: &'a A,
    process_printer: &'a dyn ProcessPrinter,
    tx_in_progress: Cell<bool>,
    tx_buffer: TakeCell<'static, [u8]>,
    queue_buffer: TakeCell<'static, [u8]>,
    queue_size: Cell<usize>,
    writer_state: Cell<WriterState>,
    rx_buffer: TakeCell<'static, [u8]>,
    command_buffer: TakeCell<'static, [u8]>,
    command_index: Cell<usize>,

    /// Operational mode the console is in. This includes if it is actively
    /// responding to commands.
    mode: Cell<ProcessConsoleState>,

    /// Escape state machine in order to process an escape sequence
    esc_state: Cell<EscState>,

    /// Keep a history of inserted commands
    command_history: MapCell<CommandHistory<'static, COMMAND_HISTORY_LEN>>,

    /// Cursor index in the current typing command
    cursor: Cell<usize>,

    /// Keep the previously read byte to consider \r\n sequences
    /// as a single \n.
    previous_byte: Cell<u8>,

    /// Internal flag that the process console should parse the command it just
    /// received after finishing echoing the last newline character.
    execute: Cell<bool>,

    /// Reference to the kernel object so we can access process state.
    kernel: &'static Kernel,

    /// Memory addresses of where the kernel is placed in memory on chip.
    kernel_addresses: KernelAddresses,

    /// Function used to reset the device in bootloader mode
    reset_function: Option<fn() -> !>,

    /// This capsule needs to use potentially dangerous APIs related to
    /// processes, and requires a capability to access those APIs.
    capability: C,
}

#[derive(Copy, Clone)]
pub struct Command {
    buf: [u8; COMMAND_BUF_LEN],
    len: usize,
}

impl Command {
    /// Write the buffer with the provided data.
    /// If the provided data's length is smaller than the buffer length,
    /// the left over bytes are not modified due to '\0' termination.
    fn write(&mut self, buf: &[u8; COMMAND_BUF_LEN]) {
        self.len = buf
            .iter()
            .position(|a| *a == EOL)
            .unwrap_or(COMMAND_BUF_LEN);

        (self.buf).copy_from_slice(buf);
    }

    fn insert_byte(&mut self, byte: u8, pos: usize) {
        for i in (pos..self.len).rev() {
            self.buf[i + 1] = self.buf[i];
        }

        if let Some(buf_byte) = self.buf.get_mut(pos) {
            *buf_byte = byte;
            self.len += 1;
        }
    }

    fn delete_byte(&mut self, pos: usize) {
        for i in pos..self.len {
            self.buf[i] = self.buf[i + 1];
        }

        if let Some(buf_byte) = self.buf.get_mut(self.len - 1) {
            *buf_byte = EOL;
            self.len -= 1;
        }
    }

    fn clear(&mut self) {
        self.buf.iter_mut().for_each(|x| *x = EOL);
        self.len = 0;
    }
}

impl Default for Command {
    fn default() -> Self {
        Command {
            buf: [EOL; COMMAND_BUF_LEN],
            len: 0,
        }
    }
}

impl PartialEq<[u8; COMMAND_BUF_LEN]> for Command {
    fn eq(&self, other_buf: &[u8; COMMAND_BUF_LEN]) -> bool {
        self.buf
            .iter()
            .zip(other_buf.iter())
            .take_while(|(a, b)| **a != EOL || **b != EOL)
            .all(|(a, b)| *a == *b)
    }
}

struct CommandHistory<'a, const COMMAND_HISTORY_LEN: usize> {
    cmds: &'a mut [Command; COMMAND_HISTORY_LEN],
    cmd_idx: usize,
    cmd_is_modified: bool,
}

impl<'a, const COMMAND_HISTORY_LEN: usize> CommandHistory<'a, COMMAND_HISTORY_LEN> {
    fn new(cmds_buffer: &'a mut [Command; COMMAND_HISTORY_LEN]) -> Self {
        Self {
            cmds: cmds_buffer,
            cmd_idx: 0,
            cmd_is_modified: false,
        }
    }

    /// Creates an empty space in the history for the next command
    fn make_space(&mut self, cmd: &[u8]) {
        let mut cmd_arr = [0; COMMAND_BUF_LEN];
        cmd_arr.copy_from_slice(cmd);

        if self.cmds[1] != cmd_arr {
            self.cmds.rotate_right(1);
            self.cmds[0].clear();
            self.cmds[1].write(&cmd_arr);
        }
    }

    fn write_to_first(&mut self, cmd: &[u8]) {
        let mut cmd_arr = [0; COMMAND_BUF_LEN];
        cmd_arr.copy_from_slice(cmd);
        self.cmds[0].write(&cmd_arr);
    }

    // Set the next index in the command history
    fn next_cmd_idx(&mut self) -> Option<usize> {
        if self.cmd_idx + 1 >= COMMAND_HISTORY_LEN {
            None
        } else if self.cmds[self.cmd_idx + 1].len == 0 {
            None
        } else {
            self.cmd_idx += 1;

            Some(self.cmd_idx)
        }
    }

    // Set the previous index in the command history
    fn prev_cmd_idx(&mut self) -> Option<usize> {
        if self.cmd_idx > 0 {
            self.cmd_idx -= 1;

            Some(self.cmd_idx)
        } else {
            None
        }
    }
}

pub struct ConsoleWriter {
    buf: [u8; 500],
    size: usize,
}
impl ConsoleWriter {
    pub fn new() -> ConsoleWriter {
        ConsoleWriter {
            buf: [EOL; 500],
            size: 0,
        }
    }
    pub fn clear(&mut self) {
        self.size = 0;
    }
}
impl fmt::Write for ConsoleWriter {
    fn write_str(&mut self, s: &str) -> fmt::Result {
        let curr = s.len();
        self.buf[self.size..self.size + curr].copy_from_slice(s.as_bytes());
        self.size += curr;
        Ok(())
    }
}

impl BinaryWrite for ConsoleWriter {
    fn write_buffer(&mut self, buffer: &[u8]) -> Result<usize, ()> {
        let start = self.size;
        let remaining = self.buf.len() - start;
        let to_send = core::cmp::min(buffer.len(), remaining);
        self.buf[start..start + to_send].copy_from_slice(&buffer[..to_send]);
        self.size += to_send;
        Ok(to_send)
    }
}

impl<
        'a,
        const COMMAND_HISTORY_LEN: usize,
        A: Alarm<'a>,
        C: ProcessManagementCapability + ProcessStartCapability,
    > ProcessConsole<'a, COMMAND_HISTORY_LEN, A, C>
{
    pub fn new(
        uart: &'a dyn uart::UartData<'a>,
        alarm: &'a A,
        process_printer: &'a dyn ProcessPrinter,
        tx_buffer: &'static mut [u8],
        rx_buffer: &'static mut [u8],
        queue_buffer: &'static mut [u8],
        cmd_buffer: &'static mut [u8],
        cmd_history_buffer: &'static mut [Command; COMMAND_HISTORY_LEN],
        kernel: &'static Kernel,
        kernel_addresses: KernelAddresses,
        reset_function: Option<fn() -> !>,
        capability: C,
    ) -> ProcessConsole<'a, COMMAND_HISTORY_LEN, A, C> {
        ProcessConsole {
            uart,
            alarm,
            process_printer,
            tx_in_progress: Cell::new(false),
            tx_buffer: TakeCell::new(tx_buffer),
            queue_buffer: TakeCell::new(queue_buffer),
            queue_size: Cell::new(0),
            writer_state: Cell::new(WriterState::Empty),
            rx_buffer: TakeCell::new(rx_buffer),
            command_buffer: TakeCell::new(cmd_buffer),
            command_index: Cell::new(0),
            mode: Cell::new(ProcessConsoleState::Off),
            esc_state: Cell::new(EscState::Bypass),
            command_history: MapCell::new(CommandHistory::new(cmd_history_buffer)),
            cursor: Cell::new(0),
            previous_byte: Cell::new(EOL),
            execute: Cell::new(false),
            kernel,
            kernel_addresses,
            reset_function,
            capability,
        }
    }

    /// Start the process console listening for user commands.
    pub fn start(&self) -> Result<(), ErrorCode> {
        if self.mode.get() == ProcessConsoleState::Off {
            self.alarm
                .set_alarm(self.alarm.now(), self.alarm.ticks_from_ms(100));
            self.mode.set(ProcessConsoleState::Active);
        }
        Ok(())
    }

    /// Start the process console listening but in a hibernated state.
    ///
    /// The process console will not respond to commands, but can be activated
    /// with the `console-start` command.
    pub fn start_hibernated(&self) -> Result<(), ErrorCode> {
        if self.mode.get() == ProcessConsoleState::Off {
            self.alarm
                .set_alarm(self.alarm.now(), self.alarm.ticks_from_ms(100));
            self.mode.set(ProcessConsoleState::Hibernating)
        }
        Ok(())
    }

    /// Print base information about the kernel version installed and the help
    /// message.
    pub fn display_welcome(&self) {
        // Start if not already started.
        if self.mode.get() == ProcessConsoleState::Off {
            self.rx_buffer.take().map(|buffer| {
                let _ = self.uart.receive_buffer(buffer, 1);
                self.mode.set(ProcessConsoleState::Active);
            });
        }

        // Display pconsole info.
        let mut console_writer = ConsoleWriter::new();
        let _ = write(
            &mut console_writer,
            format_args!(
                "Kernel version: {}.{} (build {})\r\n",
                kernel::KERNEL_MAJOR_VERSION,
                kernel::KERNEL_MINOR_VERSION,
                option_env!("TOCK_KERNEL_VERSION").unwrap_or("unknown"),
            ),
        );
        let _ = self.write_bytes(&(console_writer.buf)[..console_writer.size]);

        let _ = self.write_bytes(b"Welcome to the process console.\r\n");
        let _ = self.write_bytes(b"Valid commands are: ");
        let _ = self.write_bytes(VALID_COMMANDS_STR);
        self.prompt();
    }

    /// Simple state machine helper function that identifies the next state for
    /// printing log debug messages.
    fn next_state(&self, state: WriterState) -> WriterState {
        match state {
            WriterState::KernelStart => WriterState::KernelBss,
            WriterState::KernelBss => WriterState::KernelInit,
            WriterState::KernelInit => WriterState::KernelStack,
            WriterState::KernelStack => WriterState::KernelRoData,
            WriterState::KernelRoData => WriterState::KernelText,
            WriterState::KernelText => WriterState::Empty,
            WriterState::ProcessPrint {
                process_id,
                context,
            } => WriterState::ProcessPrint {
                process_id,
                context,
            },
            WriterState::List { index, total } => {
                // Next state just increments index, unless we are at end in
                // which next state is just the empty state.
                if index + 1 == total {
                    WriterState::Empty
                } else {
                    WriterState::List {
                        index: index + 1,
                        total,
                    }
                }
            }
            WriterState::Empty => WriterState::Empty,
        }
    }

    /// Create the debug message for each state in the state machine.
    fn create_state_buffer(&self, state: WriterState) {
        match state {
            WriterState::KernelBss => {
                let mut console_writer = ConsoleWriter::new();

                let bss_start = self.kernel_addresses.bss_start as usize;
                let bss_end = self.kernel_addresses.bss_end as usize;
                let bss_size = bss_end - bss_start;

                let _ = write(
                    &mut console_writer,
                    format_args!(
                        "\r\n ╔═══════════╤══════════════════════════════╗\
                    \r\n ║  Address  │ Region Name    Used (bytes)  ║\
                    \r\n ╚{:#010X}═╪══════════════════════════════╝\
                    \r\n             │   BSS        {:6}",
                        bss_end, bss_size
                    ),
                );

                let _ = self.write_bytes(&(console_writer.buf)[..console_writer.size]);
            }
            WriterState::KernelInit => {
                let mut console_writer = ConsoleWriter::new();

                let relocate_start = self.kernel_addresses.relocations_start as usize;
                let relocate_end = self.kernel_addresses.relocations_end as usize;
                let relocate_size = relocate_end - relocate_start;

                let _ = write(
                    &mut console_writer,
                    format_args!(
                        "\
                    \r\n  {:#010X} ┼─────────────────────────────── S\
                    \r\n             │   Relocate   {:6}            R",
                        relocate_end, relocate_size
                    ),
                );
                let _ = self.write_bytes(&(console_writer.buf)[..console_writer.size]);
            }
            WriterState::KernelStack => {
                let mut console_writer = ConsoleWriter::new();

                let stack_start = self.kernel_addresses.stack_start as usize;
                let stack_end = self.kernel_addresses.stack_end as usize;
                let stack_size = stack_end - stack_start;

                let _ = write(
                    &mut console_writer,
                    format_args!(
                        "\
                    \r\n  {:#010X} ┼─────────────────────────────── A\
                    \r\n             │ ▼ Stack      {:6}            M\
                    \r\n  {:#010X} ┼───────────────────────────────",
                        stack_end, stack_size, stack_start
                    ),
                );
                let _ = self.write_bytes(&(console_writer.buf)[..console_writer.size]);
            }
            WriterState::KernelRoData => {
                let mut console_writer = ConsoleWriter::new();

                let rodata_start = self.kernel_addresses.read_only_data_start as usize;
                let text_end = self.kernel_addresses.text_end as usize;
                let rodata_size = text_end - rodata_start;

                let _ = write(
                    &mut console_writer,
                    format_args!(
                        "\
                        \r\n             .....\
                     \r\n  {:#010X} ┼─────────────────────────────── F\
                     \r\n             │   RoData     {:6}            L",
                        text_end, rodata_size
                    ),
                );
                let _ = self.write_bytes(&(console_writer.buf)[..console_writer.size]);
            }
            WriterState::KernelText => {
                let mut console_writer = ConsoleWriter::new();

                let code_start = self.kernel_addresses.text_start as usize;
                let code_end = self.kernel_addresses.read_only_data_start as usize;
                let code_size = code_end - code_start;

                let _ = write(
                    &mut console_writer,
                    format_args!(
                        "\
                     \r\n  {:#010X} ┼─────────────────────────────── A\
                     \r\n             │   Code       {:6}            S\
                     \r\n  {:#010X} ┼─────────────────────────────── H\
                     \r\n",
                        code_end, code_size, code_start
                    ),
                );
                let _ = self.write_bytes(&(console_writer.buf)[..console_writer.size]);
            }
            WriterState::ProcessPrint {
                process_id,
                context,
            } => {
                self.kernel
                    .process_each_capability(&self.capability, |process| {
                        if process_id == process.processid() {
                            let mut console_writer = ConsoleWriter::new();
                            let new_context = self.process_printer.print_overview(
                                process,
                                &mut console_writer,
                                context,
                            );

                            let _ = self.write_bytes(&(console_writer.buf)[..console_writer.size]);

                            if new_context.is_some() {
                                self.writer_state.replace(WriterState::ProcessPrint {
                                    process_id,
                                    context: new_context,
                                });
                            } else {
                                self.writer_state.replace(WriterState::Empty);
                                // As setting the next state here to Empty does not
                                // go through this match again before reading a new command,
                                // we have to print the prompt here.
                                self.prompt();
                            }
                        }
                    });
            }
            WriterState::List { index, total: _ } => {
                let mut local_index = -1;
                self.kernel
                    .process_each_capability(&self.capability, |process| {
                        local_index += 1;
                        if local_index == index {
                            let info: KernelInfo = KernelInfo::new(self.kernel);

                            let pname = process.get_process_name();
                            let process_id = process.processid();
                            let short_id = process.short_app_id();

                            let (grants_used, grants_total) =
                                info.number_app_grant_uses(process_id, &self.capability);
                            let mut console_writer = ConsoleWriter::new();

                            // Display process id.
                            let _ = write(&mut console_writer, format_args!(" {:<7?}", process_id));
                            // Display short id.
                            match short_id {
                                kernel::process::ShortId::LocallyUnique => {
                                    let _ = write(
                                        &mut console_writer,
                                        format_args!("{}", "Unique     ",),
                                    );
                                }
                                kernel::process::ShortId::Fixed(id) => {
                                    let _ =
                                        write(&mut console_writer, format_args!("0x{:<8x} ", id));
                                }
                            }
                            // Display everything else.
                            let _ = write(
                                &mut console_writer,
                                format_args!(
                                    "{:<20}{:6}{:10}{:10}  {:2}/{:2}   {:?}\r\n",
                                    pname,
                                    process.debug_timeslice_expiration_count(),
                                    process.debug_syscall_count(),
                                    process.get_restart_count(),
                                    grants_used,
                                    grants_total,
                                    process.get_state(),
                                ),
                            );

                            let _ = self.write_bytes(&(console_writer.buf)[..console_writer.size]);
                        }
                    });
            }
            WriterState::Empty => {
                self.prompt();
            }
            _ => {}
        }
    }

    // Process the command in the command buffer and clear the buffer.
    fn read_command(&self) {
        self.command_buffer.map(|command| {
            let terminator = command.iter().position(|&x| x == 0).unwrap_or(0);

            // A command is valid only if it starts inside the buffer,
            // ends before the beginning of the buffer, and ends after
            // it starts.
            if terminator > 0 {
                let cmd_str = str::from_utf8(&command[0..terminator]);

                match cmd_str {
                    Ok(s) => {
                        let clean_str = s.trim();

                        // Check if the command history is enabled by the user
                        // and check if the command is not full of whitespaces
                        if COMMAND_HISTORY_LEN > 1 {
                            if clean_str.len() > 0 {
                                self.command_history.map(|ht| {
                                    ht.make_space(command);
                                });
                            }
                        }

                        if clean_str.starts_with("console-start") {
                            self.mode.set(ProcessConsoleState::Active);
                        } else if self.mode.get() == ProcessConsoleState::Hibernating {
                            // Ignore all commands in hibernating mode. We put
                            // this case early so we ensure we get stuck here
                            // even if the user typed a valid command.
                        } else if clean_str.starts_with("help") {
                            let _ = self.write_bytes(b"Welcome to the process console.\r\n");
                            let _ = self.write_bytes(b"Valid commands are: ");
                            let _ = self.write_bytes(VALID_COMMANDS_STR);
                        } else if clean_str.starts_with("console-stop") {
                            let _ = self.write_bytes(b"Disabling the process console.\r\n");
                            let _ = self.write_bytes(b"Run console-start to reactivate.\r\n");
                            self.mode.set(ProcessConsoleState::Hibernating);
                        } else if clean_str.starts_with("start") {
                            let argument = clean_str.split_whitespace().nth(1);
                            argument.map(|name| {
                                self.kernel
                                    .process_each_capability(&self.capability, |proc| {
                                        let proc_name = proc.get_process_name();
                                        if proc_name == name {
                                            proc.resume();
                                            let mut console_writer = ConsoleWriter::new();
                                            let _ = write(
                                                &mut console_writer,
                                                format_args!("Process {} resumed.\r\n", name),
                                            );

                                            let _ = self.write_bytes(
                                                &(console_writer.buf)[..console_writer.size],
                                            );
                                        }
                                    });
                            });
                        } else if clean_str.starts_with("stop") {
                            let argument = clean_str.split_whitespace().nth(1);
                            argument.map(|name| {
                                self.kernel
                                    .process_each_capability(&self.capability, |proc| {
                                        let proc_name = proc.get_process_name();
                                        if proc_name == name {
                                            proc.stop();
                                            let mut console_writer = ConsoleWriter::new();
                                            let _ = write(
                                                &mut console_writer,
                                                format_args!("Process {} stopped\r\n", proc_name),
                                            );

                                            let _ = self.write_bytes(
                                                &(console_writer.buf)[..console_writer.size],
                                            );
                                        }
                                    });
                            });
                        } else if clean_str.starts_with("fault") {
                            let argument = clean_str.split_whitespace().nth(1);
                            argument.map(|name| {
                                self.kernel
                                    .process_each_capability(&self.capability, |proc| {
                                        let proc_name = proc.get_process_name();
                                        if proc_name == name {
                                            proc.set_fault_state();
                                            let mut console_writer = ConsoleWriter::new();
                                            let _ = write(
                                                &mut console_writer,
                                                format_args!(
                                                    "Process {} now faulted\r\n",
                                                    proc_name
                                                ),
                                            );

                                            let _ = self.write_bytes(
                                                &(console_writer.buf)[..console_writer.size],
                                            );
                                        }
                                    });
                            });
                        } else if clean_str.starts_with("terminate") {
                            let argument = clean_str.split_whitespace().nth(1);
                            argument.map(|name| {
                                self.kernel
                                    .process_each_capability(&self.capability, |proc| {
                                        let proc_name = proc.get_process_name();
                                        if proc_name == name {
                                            proc.terminate(None);
                                            let mut console_writer = ConsoleWriter::new();
                                            let _ = write(
                                                &mut console_writer,
                                                format_args!(
                                                    "Process {} terminated\r\n",
                                                    proc_name
                                                ),
                                            );

                                            let _ = self.write_bytes(
                                                &(console_writer.buf)[..console_writer.size],
                                            );
                                        }
                                    });
                            });
                        } else if clean_str.starts_with("boot") {
                            let argument = clean_str.split_whitespace().nth(1);
                            argument.map(|name| {
                                self.kernel
                                    .process_each_capability(&self.capability, |proc| {
                                        let proc_name = proc.get_process_name();
                                        if proc_name == name
                                            && proc.get_state() == State::Terminated
                                        {
                                            proc.start(&self.capability);
                                        }
                                    });
                            });
                        } else if clean_str.starts_with("list") {
                            let _ = self
                                .write_bytes(b" PID    ShortID    Name                Quanta  ");
                            let _ = self.write_bytes(b"Syscalls  Restarts  Grants  State\r\n");

                            // Count the number of current processes.
                            let mut count = 0;
                            self.kernel.process_each_capability(&self.capability, |_| {
                                count += 1;
                            });

                            if count > 0 {
                                // Start the state machine to print each separately.
                                self.write_state(WriterState::List {
                                    index: -1,
                                    total: count,
                                });
                            }
                        } else if clean_str.starts_with("status") {
                            let info: KernelInfo = KernelInfo::new(self.kernel);
                            let mut console_writer = ConsoleWriter::new();
                            let _ = write(
                                &mut console_writer,
                                format_args!(
                                    "Total processes: {}\r\n",
                                    info.number_loaded_processes(&self.capability)
                                ),
                            );
                            let _ = self.write_bytes(&(console_writer.buf)[..console_writer.size]);
                            console_writer.clear();
                            let _ = write(
                                &mut console_writer,
                                format_args!(
                                    "Active processes: {}\r\n",
                                    info.number_active_processes(&self.capability)
                                ),
                            );
                            let _ = self.write_bytes(&(console_writer.buf)[..console_writer.size]);
                            console_writer.clear();
                            let _ = write(
                                &mut console_writer,
                                format_args!(
                                    "Timeslice expirations: {}\r\n",
                                    info.timeslice_expirations(&self.capability)
                                ),
                            );
                            let _ = self.write_bytes(&(console_writer.buf)[..console_writer.size]);
                        } else if clean_str.starts_with("process") {
                            let argument = clean_str.split_whitespace().nth(1);
                            argument.map(|name| {
                                // If two processes have the same name, only
                                // print the first one we find.
                                let mut found = false;
                                self.kernel
                                    .process_each_capability(&self.capability, |proc| {
                                        if found {
                                            return;
                                        }
                                        let proc_name = proc.get_process_name();
                                        if proc_name == name {
                                            let mut console_writer = ConsoleWriter::new();
                                            let mut context: Option<ProcessPrinterContext> = None;
                                            context = self.process_printer.print_overview(
                                                proc,
                                                &mut console_writer,
                                                context,
                                            );

                                            let _ = self.write_bytes(
                                                &(console_writer.buf)[..console_writer.size],
                                            );

                                            if context.is_some() {
                                                self.writer_state.replace(
                                                    WriterState::ProcessPrint {
                                                        process_id: proc.processid(),
                                                        context,
                                                    },
                                                );
                                            }

                                            found = true;
                                        }
                                    });
                            });
                        } else if clean_str.starts_with("kernel") {
                            let mut console_writer = ConsoleWriter::new();
                            let _ = write(
                                &mut console_writer,
                                format_args!(
                                    "Kernel version: {}.{} (build {})\r\n",
                                    kernel::KERNEL_MAJOR_VERSION,
                                    kernel::KERNEL_MINOR_VERSION,
                                    option_env!("TOCK_KERNEL_VERSION").unwrap_or("unknown")
                                ),
                            );
                            let _ = self.write_bytes(&(console_writer.buf)[..console_writer.size]);
                            console_writer.clear();

                            // Prints kernel memory by moving the writer to the
                            // start state.
                            self.writer_state.replace(WriterState::KernelStart);
                        } else if clean_str.starts_with("reset") {
                            self.reset_function.map_or_else(
                                || {
                                    let _ = self.write_bytes(b"Reset function is not implemented");
                                },
                                |f| {
                                    f();
                                },
                            );
                        } else if clean_str.starts_with("panic") {
                            panic!("Process Console forced a kernel panic.");
                        } else {
                            let _ = self.write_bytes(b"Valid commands are: ");
                            let _ = self.write_bytes(VALID_COMMANDS_STR);
                        }
                    }
                    Err(_e) => {
                        let mut console_writer = ConsoleWriter::new();
                        let _ = write(
                            &mut console_writer,
                            format_args!("Invalid command: {:?}", command),
                        );
                        let _ = self.write_bytes(&(console_writer.buf)[..console_writer.size]);
                    }
                }
            }
        });
        self.command_buffer.map(|command| {
            command[0] = 0;
        });
        self.command_index.set(0);
        if self.writer_state.get() == WriterState::Empty {
            self.prompt();
        }
    }

    fn prompt(&self) {
        // Only display the prompt in active mode.
        match self.mode.get() {
            ProcessConsoleState::Active => {
                let _ = self.write_bytes(b"tock$ ");
            }
            _ => {}
        }
    }

    /// Start or iterate the state machine for an asynchronous write operation
    /// spread across multiple callback cycles.
    fn write_state(&self, state: WriterState) {
        self.writer_state.replace(self.next_state(state));
        self.create_state_buffer(self.writer_state.get());
    }

    fn write_byte(&self, byte: u8) -> Result<(), ErrorCode> {
        if self.tx_in_progress.get() {
            self.queue_buffer.map(|buf| {
                buf[self.queue_size.get()] = byte;
                self.queue_size.set(self.queue_size.get() + 1);
            });
            Err(ErrorCode::BUSY)
        } else {
            self.tx_in_progress.set(true);
            self.tx_buffer.take().map(|buffer| {
                buffer[0] = byte;
                let _ = self.uart.transmit_buffer(buffer, 1);
            });
            Ok(())
        }
    }

    fn write_bytes(&self, bytes: &[u8]) -> Result<(), ErrorCode> {
        if self.tx_in_progress.get() {
            self.queue_buffer.map(|buf| {
                let size = self.queue_size.get();
                let len = cmp::min(bytes.len(), buf.len() - size);
                (buf[size..size + len]).copy_from_slice(&bytes[..len]);
                self.queue_size.set(size + len);
            });
            Err(ErrorCode::BUSY)
        } else {
            self.tx_in_progress.set(true);
            self.tx_buffer.take().map(|buffer| {
                let len = cmp::min(bytes.len(), buffer.len());
                // Copy elements of `bytes` into `buffer`
                (buffer[..len]).copy_from_slice(&bytes[..len]);
                let _ = self.uart.transmit_buffer(buffer, len);
            });
            Ok(())
        }
    }

    /// If there is anything in the queue, copy it to the TX buffer and send
    /// it to the UART.
    ///
    /// Returns Ok(usize) with the number of bytes sent from the queue. If Ok(0)
    /// is returned, nothing was sent and the UART is free.
    fn handle_queue(&self) -> Result<usize, ErrorCode> {
        if self.tx_in_progress.get() {
            // This shouldn't happen because we should only try to handle the
            // queue when nothing else is happening, but still have the check
            // for safety.
            return Err(ErrorCode::BUSY);
        }

        self.queue_buffer.map_or(Err(ErrorCode::FAIL), |qbuf| {
            let qlen = self.queue_size.get();

            if qlen > 0 {
                self.tx_buffer.take().map_or(Err(ErrorCode::FAIL), |txbuf| {
                    let txlen = cmp::min(qlen, txbuf.len());

                    // Copy elements of the queue into the TX buffer.
                    (txbuf[..txlen]).copy_from_slice(&qbuf[..txlen]);

                    // TODO: If the queue needs to print over multiple TX
                    // buffers, we need to shift the remaining contents of the
                    // queue back to index 0.
                    // if qlen > txlen {
                    //     (&mut qbuf[txlen..qlen]).copy_from_slice(&qbuf[txlen..qlen]);
                    // }

                    // Mark that we sent at least some of the queue.
                    let remaining = qlen - txlen;
                    self.queue_size.set(remaining);

                    self.tx_in_progress.set(true);
                    let _ = self.uart.transmit_buffer(txbuf, txlen);
                    Ok(txlen)
                })
            } else {
                // Queue was empty, nothing to do.
                Ok(0)
            }
        })
    }
}

impl<
        'a,
        const COMMAND_HISTORY_LEN: usize,
        A: Alarm<'a>,
        C: ProcessManagementCapability + ProcessStartCapability,
    > AlarmClient for ProcessConsole<'a, COMMAND_HISTORY_LEN, A, C>
{
    fn alarm(&self) {
        self.prompt();
        self.rx_buffer.take().map(|buffer| {
            let _ = self.uart.receive_buffer(buffer, 1);
        });
    }
}

impl<
        'a,
        const COMMAND_HISTORY_LEN: usize,
        A: Alarm<'a>,
        C: ProcessManagementCapability + ProcessStartCapability,
    > uart::TransmitClient for ProcessConsole<'a, COMMAND_HISTORY_LEN, A, C>
{
    fn transmitted_buffer(
        &self,
        buffer: &'static mut [u8],
        _tx_len: usize,
        _rcode: Result<(), ErrorCode>,
    ) {
        // Reset state now that we no longer have an active transmission on the
        // UART.
        self.tx_buffer.replace(buffer);
        self.tx_in_progress.set(false);

        // Check if we have anything queued up. If we do, let the queue
        // empty.
        let ret = self.handle_queue();
        if ret.ok() == Some(0) || ret.is_err() {
            // The queue was empty or we couldn't print the queue.

            let current_state = self.writer_state.get();
            if current_state != WriterState::Empty {
                self.write_state(current_state);
                return;
            }

            // Check if we just received and echoed a newline character, and
            // therefore need to process the received message.
            if self.execute.get() {
                self.execute.set(false);
                self.read_command();
            }
        }
    }
}

impl<
        'a,
        const COMMAND_HISTORY_LEN: usize,
        A: Alarm<'a>,
        C: ProcessManagementCapability + ProcessStartCapability,
    > uart::ReceiveClient for ProcessConsole<'a, COMMAND_HISTORY_LEN, A, C>
{
    fn received_buffer(
        &self,
        read_buf: &'static mut [u8],
        rx_len: usize,
        _rcode: Result<(), ErrorCode>,
        error: uart::Error,
    ) {
        if error == uart::Error::None {
            match rx_len {
                0 => debug!("ProcessConsole had read of 0 bytes"),
                1 => {
                    self.command_buffer.map(|command| {
                        let esc_state = self.esc_state.get().next_state(read_buf[0]);
                        self.esc_state.set(esc_state);

                        let previous_byte = self.previous_byte.get();
                        self.previous_byte.set(read_buf[0]);
                        let index = self.command_index.get();

                        let cursor = self.cursor.get();

                        if let EscState::Complete(key) = esc_state {
                            match key {
                                EscKey::Up | EscKey::Down if COMMAND_HISTORY_LEN >= 1 => {
                                    self.command_history.map(|ht| {
                                        if let Some(next_index) = if matches!(key, EscKey::Up) {
                                            ht.next_cmd_idx()
                                        } else {
                                            ht.prev_cmd_idx()
                                        } {
                                            let next_command_len = ht.cmds[next_index].len;

                                            for _ in cursor..index {
                                                let _ = self.write_byte(SPACE);
                                            }

                                            // Clear the displayed command
                                            for _ in 0..index {
                                                let _ = self.write_bytes(&[BS, SPACE, BS]);
                                            }

                                            // Display the new command
                                            for i in 0..next_command_len {
                                                let byte = ht.cmds[next_index].buf[i];
                                                let _ = self.write_byte(byte);
                                                command[i] = byte;
                                            }

                                            ht.cmd_is_modified = true;
                                            self.command_index.set(next_command_len);
                                            self.cursor.set(next_command_len);
                                            command[next_command_len] = EOL;
                                        };
                                    });
                                }
                                EscKey::Left if cursor > 0 => {
                                    let _ = self.write_byte(BS);
                                    self.cursor.set(cursor - 1);
                                }
                                EscKey::Right if cursor < index => {
                                    let _ = self.write_byte(command[cursor]);
                                    self.cursor.set(cursor + 1);
                                }
                                EscKey::Home if cursor > 0 => {
                                    for _ in 0..cursor {
                                        let _ = self.write_byte(BS);
                                    }

                                    self.cursor.set(0);
                                }
                                EscKey::End if cursor < index => {
                                    for i in cursor..index {
                                        let _ = self.write_byte(command[i]);
                                    }

                                    self.cursor.set(index);
                                }
                                EscKey::Delete if cursor < index => {
                                    // Move the bytes one position to left
                                    for i in cursor..(index - 1) {
                                        command[i] = command[i + 1];
                                        let _ = self.write_byte(command[i]);
                                    }
                                    // We don't want to write the EOL byte, but we want to copy it to the left
                                    command[index - 1] = command[index];

                                    // Now that we copied all bytes to the left, we are left over with
                                    // a dublicate "ghost" character of the last byte,
                                    // In case we deleted the first character, this doesn't do anything as
                                    // the dublicate is not there.
                                    // |abcdef -> bcdef
                                    // abc|def -> abceff -> abcef
                                    let _ = self.write_bytes(&[SPACE, BS]);

                                    // Move the cursor to last position
                                    for _ in cursor..(index - 1) {
                                        let _ = self.write_byte(BS);
                                    }

                                    self.command_index.set(index - 1);

                                    // Remove the byte from the command in order
                                    // not to permit accumulation of the text
                                    if COMMAND_HISTORY_LEN > 1 {
                                        self.command_history.map(|ht| {
                                            if ht.cmd_is_modified {
                                                // Copy the last command into the unfinished command

                                                ht.cmds[0].clear();
                                                ht.write_to_first(command);
                                                ht.cmd_is_modified = false;
                                            } else {
                                                ht.cmds[0].delete_byte(cursor);
                                            }
                                        });
                                    }
                                }
                                _ => {}
                            };
                        } else if read_buf[0] == NLINE || read_buf[0] == CR {
                            if (previous_byte == NLINE || previous_byte == CR)
                                && previous_byte != read_buf[0]
                            {
                                // Reset the sequence, when \r\n is received
                                self.previous_byte.set(EOL);
                            } else {
                                self.cursor.set(0);
                                self.execute.set(true);

                                let _ = self.write_bytes(&[CR, NLINE]);

                                if COMMAND_HISTORY_LEN > 1 {
                                    // Clear the unfinished command
                                    self.command_history.map(|ht| {
                                        ht.cmd_idx = 0;
                                        ht.cmd_is_modified = false;
                                        ht.cmds[0].clear();
                                    });
                                }
                            }
                        } else if read_buf[0] == BS {
                            if cursor > 0 {
                                // Backspace, echo and remove the byte
                                // preceding the cursor
                                // Note echo is '\b \b' to erase
                                let _ = self.write_bytes(&[BS, SPACE, BS]);

                                // Move the bytes one position to left
                                for i in (cursor - 1)..(index - 1) {
                                    command[i] = command[i + 1];
                                    let _ = self.write_byte(command[i]);
                                }
                                // We don't want to write the EOL byte, but we want to copy it to the left
                                command[index - 1] = command[index];

                                // Now that we copied all bytes to the left, we are left over with
                                // a dublicate "ghost" character of the last byte,
                                // In case we deleted the last character, this doesn't do anything as
                                // the dublicate is not there.
                                // abcdef| -> abcdef
                                // abcd|ef -> abceff -> abcef
                                let _ = self.write_bytes(&[SPACE, BS]);

                                // Move the cursor to last position
                                for _ in cursor..index {
                                    let _ = self.write_byte(BS);
                                }

                                self.command_index.set(index - 1);
                                self.cursor.set(cursor - 1);

                                // Remove the byte from the command in order
                                // not to permit accumulation of the text
                                if COMMAND_HISTORY_LEN > 1 {
                                    self.command_history.map(|ht| {
                                        if ht.cmd_is_modified {
                                            // Copy the last command into the unfinished command

                                            ht.cmds[0].clear();
                                            ht.write_to_first(command);
                                            ht.cmd_is_modified = false;
                                        } else {
                                            ht.cmds[0].delete_byte(cursor - 1);
                                        }
                                    });
                                }
                            }
                        } else if index < (command.len() - 1)
                            && read_buf[0] < ASCII_LIMIT
                            && !esc_state.has_started()
                            && !esc_state.in_progress()
                        {
                            // For some reason, sometimes reads return > 127 but no error,
                            // which causes utf-8 decoding failure, so check byte is < 128. -pal

                            // Echo the typed byte
                            let _ = self.write_byte(read_buf[0]);

                            // Echo the rest of the bytes from the command
                            for i in cursor..index {
                                let _ = self.write_byte(command[i]);
                            }

                            // Make space for the newest byte
                            for i in (cursor..(index + 1)).rev() {
                                command[i + 1] = command[i];
                            }

                            // Move the cursor to the last position
                            for _ in cursor..index {
                                let _ = self.write_byte(BS);
                            }

                            command[cursor] = read_buf[0];
                            self.cursor.set(cursor + 1);
                            self.command_index.set(index + 1);

                            if COMMAND_HISTORY_LEN > 1 {
                                self.command_history.map(|ht| {
                                    if ht.cmd_is_modified {
                                        // Copy the last command into the unfinished command

                                        ht.cmds[0].clear();
                                        ht.write_to_first(command);
                                        ht.cmd_is_modified = false;
                                    } else {
                                        ht.cmds[0].insert_byte(read_buf[0], cursor);
                                    }
                                });
                            }
                        }
                    });
                }
                _ => debug!(
                    "ProcessConsole issues reads of 1 byte, but receive_complete was length {}",
                    rx_len
                ),
            };
        }
        let _ = self.uart.receive_buffer(read_buf, 1);
    }
}