Move to ASF4 and introduce SAMD51 support. (#258)3.0.0-alpha.0

* atmel-samd: Remove ASF3. This will break builds.

* atmel-samd: Add ASF4 for the SAMD21 and SAMD51.

* Introduce the supervisor concept to facilitate porting.

The supervisor is the code which runs individual MicroPython VMs. By
splitting it out we make it more consistent and easier to find.

This also adds very basic SAMD21 and SAMD51 support using the
supervisor. Only the REPL currently works.

This begins the work for #178.

1 files changed, 0 insertions, 779 deletions

diff --git a/atmel-samd/main.c b/atmel-samd/main.c
deleted file mode 100644
index 3a2d5a63c..000000000
--- a/atmel-samd/main.c
+++ /dev/null
@@ -1,779 +0,0 @@
-/*
- * This file is part of the MicroPython project, http://micropython.org/
- *
- * The MIT License (MIT)
- *
- * Copyright (c) 2016 Scott Shawcroft for Adafruit Industries
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-#include <stdint.h>
-#include <string.h>
-
-#include "py/nlr.h"
-#include "py/compile.h"
-#include "py/frozenmod.h"
-#include "py/mphal.h"
-#include "py/runtime.h"
-#include "py/repl.h"
-#include "py/gc.h"
-#include "py/stackctrl.h"
-
-#include "extmod/vfs_fat.h"
-#include "lib/oofatfs/ff.h"
-#include "lib/oofatfs/diskio.h"
-#include "lib/mp-readline/readline.h"
-#include "lib/utils/pyexec.h"
-
-#include "asf/common/services/sleepmgr/sleepmgr.h"
-#include "asf/common/services/usb/udc/udc.h"
-#include "asf/common2/services/delay/delay.h"
-#include "asf/sam0/drivers/nvm/nvm.h"
-#include "asf/sam0/drivers/port/port.h"
-#include "asf/sam0/drivers/sercom/usart/usart.h"
-#include "asf/sam0/drivers/system/system.h"
-#include <board.h>
-
-#include "boards/board.h"
-
-#include "common-hal/analogio/AnalogIn.h"
-#include "common-hal/audioio/AudioOut.h"
-#include "common-hal/audiobusio/PDMIn.h"
-#include "common-hal/pulseio/PulseIn.h"
-#include "common-hal/pulseio/PulseOut.h"
-#include "common-hal/pulseio/PWMOut.h"
-#include "common-hal/usb_hid/__init__.h"
-
-#include "autoreload.h"
-#include "flash_api.h"
-#include "mpconfigboard.h"
-#include "rgb_led_status.h"
-#include "shared_dma.h"
-#include "tick.h"
-
-#ifdef EXPRESS_BOARD
-#include "common-hal/touchio/TouchIn.h"
-#define INTERNAL_CIRCUITPY_CONFIG_START_ADDR (0x00040000 - 0x100 - CIRCUITPY_INTERNAL_NVM_SIZE)
-#else
-#define INTERNAL_CIRCUITPY_CONFIG_START_ADDR (0x00040000 - 0x010000 - 0x100 - CIRCUITPY_INTERNAL_NVM_SIZE)
-#endif
-
-fs_user_mount_t fs_user_mount_flash;
-mp_vfs_mount_t mp_vfs_mount_flash;
-
-typedef enum {
-    NO_SAFE_MODE = 0,
-    BROWNOUT,
-    HARD_CRASH,
-    USER_SAFE_MODE,
-} safe_mode_t;
-
-void do_str(const char *src, mp_parse_input_kind_t input_kind) {
-    mp_lexer_t *lex = mp_lexer_new_from_str_len(MP_QSTR__lt_stdin_gt_, src, strlen(src), 0);
-    if (lex == NULL) {
-        printf("MemoryError: lexer could not allocate memory\n");
-        return;
-    }
-
-    nlr_buf_t nlr;
-    if (nlr_push(&nlr) == 0) {
-        qstr source_name = lex->source_name;
-        mp_parse_tree_t parse_tree = mp_parse(lex, input_kind);
-        mp_obj_t module_fun = mp_compile(&parse_tree, source_name, MP_EMIT_OPT_NONE, true);
-        mp_call_function_0(module_fun);
-        nlr_pop();
-    } else {
-        // uncaught exception
-        mp_obj_print_exception(&mp_plat_print, (mp_obj_t)nlr.ret_val);
-    }
-}
-
-// we don't make this function static because it needs a lot of stack and we
-// want it to be executed without using stack within main() function
-void init_flash_fs(void) {
-    // init the vfs object
-    fs_user_mount_t *vfs_fat = &fs_user_mount_flash;
-    vfs_fat->flags = 0;
-    flash_init_vfs(vfs_fat);
-
-    // try to mount the flash
-    FRESULT res = f_mount(&vfs_fat->fatfs);
-
-    if (res == FR_NO_FILESYSTEM) {
-        // no filesystem so create a fresh one
-
-        uint8_t working_buf[_MAX_SS];
-        res = f_mkfs(&vfs_fat->fatfs, FM_FAT, 0, working_buf, sizeof(working_buf));
-        // Flush the new file system to make sure its repaired immediately.
-        flash_flush();
-        if (res != FR_OK) {
-            return;
-        }
-
-        // set label
-        f_setlabel(&vfs_fat->fatfs, "CIRCUITPY");
-    } else if (res != FR_OK) {
-        return;
-    }
-    mp_vfs_mount_t *vfs = &mp_vfs_mount_flash;
-    vfs->str = "/";
-    vfs->len = 1;
-    vfs->obj = MP_OBJ_FROM_PTR(vfs_fat);
-    vfs->next = NULL;
-    MP_STATE_VM(vfs_mount_table) = vfs;
-
-    // The current directory is used as the boot up directory.
-    // It is set to the internal flash filesystem by default.
-    MP_STATE_PORT(vfs_cur) = vfs;
-}
-
-static char heap[16384 + 4096];
-
-void reset_mp(void) {
-    reset_status_led();
-    new_status_color(0x8f008f);
-    autoreload_stop();
-
-    // Sync the file systems in case any used RAM from the GC to cache. As soon
-    // as we re-init the GC all bets are off on the cache.
-    flash_flush();
-
-    // Clear the readline history. It references the heap we're about to destroy.
-    readline_init0();
-
-    #if MICROPY_ENABLE_GC
-    gc_init(heap, heap + sizeof(heap));
-    #endif
-    mp_init();
-    mp_obj_list_init(mp_sys_path, 0);
-    mp_obj_list_append(mp_sys_path, MP_OBJ_NEW_QSTR(MP_QSTR_)); // current dir (or base dir of the script)
-    mp_obj_list_append(mp_sys_path, MP_OBJ_NEW_QSTR(MP_QSTR__slash_));
-    mp_obj_list_append(mp_sys_path, MP_OBJ_NEW_QSTR(MP_QSTR__slash_lib));
-    // Frozen modules are in their own pseudo-dir, e.g., ".frozen".
-    mp_obj_list_append(mp_sys_path, MP_OBJ_NEW_QSTR(MP_FROZEN_FAKE_DIR_QSTR));
-
-    mp_obj_list_init(mp_sys_argv, 0);
-}
-
-extern volatile bool mp_msc_enabled;
-
-void reset_samd21(void) {
-    // Reset all SERCOMs except the one being used by the SPI flash.
-    Sercom *sercom_instances[SERCOM_INST_NUM] = SERCOM_INSTS;
-    for (int i = 0; i < SERCOM_INST_NUM; i++) {
-        #ifdef SPI_FLASH_SERCOM
-            if (sercom_instances[i] == SPI_FLASH_SERCOM) {
-                continue;
-            }
-        #endif
-        #ifdef MICROPY_HW_APA102_SERCOM
-            if (sercom_instances[i] == MICROPY_HW_APA102_SERCOM) {
-                continue;
-            }
-        #endif
-        sercom_instances[i]->SPI.CTRLA.bit.SWRST = 1;
-    }
-
-#ifdef EXPRESS_BOARD
-    audioout_reset();
-    touchin_reset();
-    pdmin_reset();
-    pulsein_reset();
-    pulseout_reset();
-    pwmout_reset();
-#endif
-
-    analogin_reset();
-
-
-    // Wait for the DAC to sync then reset.
-    while (DAC->STATUS.reg & DAC_STATUS_SYNCBUSY) {}
-    DAC->CTRLA.reg |= DAC_CTRLA_SWRST;
-
-    reset_all_pins();
-
-
-    usb_hid_reset();
-
-#ifdef CALIBRATE_CRYSTALLESS
-    // If we are on USB lets double check our fine calibration for the clock and
-    // save the new value if its different enough.
-    if (mp_msc_enabled) {
-        SYSCTRL->DFLLSYNC.bit.READREQ = 1;
-        uint16_t saved_calibration = 0x1ff;
-        if (strcmp((char*) INTERNAL_CIRCUITPY_CONFIG_START_ADDR, "CIRCUITPYTHON1") == 0) {
-            saved_calibration = ((uint16_t *) INTERNAL_CIRCUITPY_CONFIG_START_ADDR)[8];
-        }
-        while (SYSCTRL->PCLKSR.bit.DFLLRDY == 0) {
-            // TODO(tannewt): Run the mass storage stuff if this takes a while.
-        }
-        int16_t current_calibration = SYSCTRL->DFLLVAL.bit.FINE;
-        if (abs(current_calibration - saved_calibration) > 10) {
-            enum status_code error_code;
-            uint8_t page_buffer[NVMCTRL_ROW_SIZE];
-            for (int i = 0; i < NVMCTRL_ROW_PAGES; i++) {
-                do
-                {
-                    error_code = nvm_read_buffer(INTERNAL_CIRCUITPY_CONFIG_START_ADDR + i * NVMCTRL_PAGE_SIZE,
-                                                 page_buffer + i * NVMCTRL_PAGE_SIZE,
-                                                 NVMCTRL_PAGE_SIZE);
-                } while (error_code == STATUS_BUSY);
-            }
-            // If this is the first write, include the header.
-            if (strcmp((char*) page_buffer, "CIRCUITPYTHON1") != 0) {
-                memcpy(page_buffer, "CIRCUITPYTHON1", 15);
-            }
-            // First 16 bytes (0-15) are ID. Little endian!
-            page_buffer[16] = current_calibration & 0xff;
-            page_buffer[17] = current_calibration >> 8;
-            do
-            {
-                error_code = nvm_erase_row(INTERNAL_CIRCUITPY_CONFIG_START_ADDR);
-            } while (error_code == STATUS_BUSY);
-            for (int i = 0; i < NVMCTRL_ROW_PAGES; i++) {
-                do
-                {
-                    error_code = nvm_write_buffer(INTERNAL_CIRCUITPY_CONFIG_START_ADDR + i * NVMCTRL_PAGE_SIZE,
-                                                  page_buffer + i * NVMCTRL_PAGE_SIZE,
-                                                  NVMCTRL_PAGE_SIZE);
-                } while (error_code == STATUS_BUSY);
-            }
-        }
-    }
-#endif
-}
-
-bool maybe_run(const char* filename, pyexec_result_t* exec_result) {
-    mp_import_stat_t stat = mp_import_stat(filename);
-    if (stat != MP_IMPORT_STAT_FILE) {
-        return false;
-    }
-    mp_hal_stdout_tx_str(filename);
-    mp_hal_stdout_tx_str(" output:\r\n");
-    pyexec_file(filename, exec_result);
-    return true;
-}
-
-bool start_mp(safe_mode_t safe_mode) {
-    bool cdc_enabled_at_start = mp_cdc_enabled;
-    #ifdef CIRCUITPY_AUTORELOAD_DELAY_MS
-    if (cdc_enabled_at_start) {
-        mp_hal_stdout_tx_str("\r\n");
-        if (autoreload_is_enabled()) {
-            mp_hal_stdout_tx_str("Auto-reload is on. Simply save files over USB to run them or enter REPL to disable.\r\n");
-        } else if (safe_mode != NO_SAFE_MODE) {
-            mp_hal_stdout_tx_str("Running in safe mode! Auto-reload is off.\r\n");
-        } else if (!autoreload_is_enabled()) {
-            mp_hal_stdout_tx_str("Auto-reload is off.\r\n");
-        }
-    }
-    #endif
-
-    pyexec_result_t result;
-    bool found_main = false;
-    if (safe_mode != NO_SAFE_MODE) {
-        mp_hal_stdout_tx_str("Running in safe mode! Not running saved code.\r\n");
-    } else {
-        new_status_color(MAIN_RUNNING);
-        found_main = maybe_run("code.txt", &result) ||
-                     maybe_run("code.py", &result) ||
-                     maybe_run("main.py", &result) ||
-                     maybe_run("main.txt", &result);
-        reset_status_led();
-
-        if (result.return_code & PYEXEC_FORCED_EXIT) {
-            return reload_next_character;
-        }
-
-        // If not is USB mode then do not skip the repl.
-        #ifndef USB_REPL
-        return false;
-        #endif
-    }
-
-    // Wait for connection or character.
-    bool cdc_enabled_before = false;
-    #if defined(MICROPY_HW_NEOPIXEL) || (defined(MICROPY_HW_APA102_MOSI) && defined(MICROPY_HW_APA102_SCK))
-    new_status_color(ALL_DONE);
-    uint32_t pattern_start = ticks_ms;
-
-    uint32_t total_exception_cycle = 0;
-    uint8_t ones = result.exception_line % 10;
-    ones += ones > 0 ? 1 : 0;
-    uint8_t tens = (result.exception_line / 10) % 10;
-    tens += tens > 0 ? 1 : 0;
-    uint8_t hundreds = (result.exception_line / 100) % 10;
-    hundreds += hundreds > 0 ? 1 : 0;
-    uint8_t thousands = (result.exception_line / 1000) % 10;
-    thousands += thousands > 0 ? 1 : 0;
-    uint8_t digit_sum = ones + tens + hundreds + thousands;
-    uint8_t num_places = 0;
-    uint16_t line = result.exception_line;
-    for (int i = 0; i < 4; i++) {
-        if ((line % 10) > 0) {
-            num_places++;
-        }
-        line /= 10;
-    }
-    if (result.return_code == PYEXEC_EXCEPTION) {
-        total_exception_cycle = EXCEPTION_TYPE_LENGTH_MS * 3 + LINE_NUMBER_TOGGLE_LENGTH * digit_sum + LINE_NUMBER_TOGGLE_LENGTH * num_places;
-    }
-    #endif
-    while (true) {
-        #ifdef MICROPY_VM_HOOK_LOOP
-            MICROPY_VM_HOOK_LOOP
-        #endif
-        if (reload_next_character) {
-            return true;
-        }
-        if (usb_rx_count > 0) {
-            // Skip REPL if reload was requested.
-            return receive_usb() == CHAR_CTRL_D;
-        }
-
-        if (!cdc_enabled_before && mp_cdc_enabled) {
-            if (cdc_enabled_at_start) {
-                mp_hal_stdout_tx_str("\r\n\r\n");
-            }
-
-            if (!cdc_enabled_at_start) {
-                if (autoreload_is_enabled()) {
-                    mp_hal_stdout_tx_str("Auto-reload is on. Simply save files over USB to run them or enter REPL to disable.\r\n");
-                } else {
-                    mp_hal_stdout_tx_str("Auto-reload is off.\r\n");
-                }
-            }
-            // Output a user safe mode string if its set.
-            #ifdef BOARD_USER_SAFE_MODE
-            if (safe_mode == USER_SAFE_MODE) {
-                mp_hal_stdout_tx_str("\r\nYou requested starting safe mode by ");
-                mp_hal_stdout_tx_str(BOARD_USER_SAFE_MODE);
-                mp_hal_stdout_tx_str(".\r\nTo exit, please reset the board without ");
-                mp_hal_stdout_tx_str(BOARD_USER_SAFE_MODE);
-                mp_hal_stdout_tx_str(".\r\n");
-            } else
-            #endif
-            if (safe_mode != NO_SAFE_MODE) {
-                mp_hal_stdout_tx_str("\r\nYou are running in safe mode which means something really bad happened.\r\n");
-                if (safe_mode == HARD_CRASH) {
-                    mp_hal_stdout_tx_str("Looks like our core CircuitPython code crashed hard. Whoops!\r\n");
-                    mp_hal_stdout_tx_str("Please file an issue here with the contents of your CIRCUITPY drive:\r\n");
-                    mp_hal_stdout_tx_str("https://github.com/adafruit/circuitpython/issues\r\n");
-                } else if (safe_mode == BROWNOUT) {
-                    mp_hal_stdout_tx_str("The microcontroller's power dipped. Please make sure your power supply provides \r\n");
-                    mp_hal_stdout_tx_str("enough power for the whole circuit and press reset (after ejecting CIRCUITPY).\r\n");
-                }
-            }
-            mp_hal_stdout_tx_str("\r\nPress any key to enter the REPL. Use CTRL-D to reload.\r\n");
-        }
-        if (cdc_enabled_before && !mp_cdc_enabled) {
-            cdc_enabled_at_start = false;
-        }
-        cdc_enabled_before = mp_cdc_enabled;
-
-        #if defined(MICROPY_HW_NEOPIXEL) || (defined(MICROPY_HW_APA102_MOSI) && defined(MICROPY_HW_APA102_SCK))
-        uint32_t tick_diff = ticks_ms - pattern_start;
-        if (result.return_code != PYEXEC_EXCEPTION) {
-            // All is good. Ramp ALL_DONE up and down.
-            if (tick_diff > ALL_GOOD_CYCLE_MS) {
-                pattern_start = ticks_ms;
-                tick_diff = 0;
-            }
-
-            uint16_t brightness = tick_diff * 255 / (ALL_GOOD_CYCLE_MS / 2);
-            if (brightness > 255) {
-                brightness = 511 - brightness;
-            }
-            if (safe_mode == NO_SAFE_MODE) {
-                new_status_color(color_brightness(ALL_DONE, brightness));
-            } else {
-                new_status_color(color_brightness(SAFE_MODE, brightness));
-            }
-        } else {
-            if (tick_diff > total_exception_cycle) {
-                pattern_start = ticks_ms;
-                tick_diff = 0;
-            }
-            // First flash the file color.
-            if (tick_diff < EXCEPTION_TYPE_LENGTH_MS) {
-                if (found_main) {
-                    new_status_color(MAIN_RUNNING);
-                } else {
-                    new_status_color(BOOT_RUNNING);
-                }
-            // Next flash the exception color.
-            } else if (tick_diff < EXCEPTION_TYPE_LENGTH_MS * 2) {
-                if (mp_obj_is_subclass_fast(result.exception_type, &mp_type_IndentationError)) {
-                    new_status_color(INDENTATION_ERROR);
-                } else if (mp_obj_is_subclass_fast(result.exception_type, &mp_type_SyntaxError)) {
-                    new_status_color(SYNTAX_ERROR);
-                } else if (mp_obj_is_subclass_fast(result.exception_type, &mp_type_NameError)) {
-                    new_status_color(NAME_ERROR);
-                } else if (mp_obj_is_subclass_fast(result.exception_type, &mp_type_OSError)) {
-                    new_status_color(OS_ERROR);
-                } else if (mp_obj_is_subclass_fast(result.exception_type, &mp_type_ValueError)) {
-                    new_status_color(VALUE_ERROR);
-                } else {
-                    new_status_color(OTHER_ERROR);
-                }
-            // Finally flash the line number digits from highest to lowest.
-            // Zeroes will not produce a flash but can be read by the absence of
-            // a color from the sequence.
-            } else if (tick_diff < (EXCEPTION_TYPE_LENGTH_MS * 2 + LINE_NUMBER_TOGGLE_LENGTH * digit_sum)) {
-                uint32_t digit_diff = tick_diff - EXCEPTION_TYPE_LENGTH_MS * 2;
-                if ((digit_diff % LINE_NUMBER_TOGGLE_LENGTH) < (LINE_NUMBER_TOGGLE_LENGTH / 2)) {
-                    new_status_color(BLACK);
-                } else if (digit_diff < LINE_NUMBER_TOGGLE_LENGTH * thousands) {
-                    if (digit_diff < LINE_NUMBER_TOGGLE_LENGTH) {
-                        new_status_color(BLACK);
-                    } else {
-                        new_status_color(THOUSANDS);
-                    }
-                } else if (digit_diff < LINE_NUMBER_TOGGLE_LENGTH * (thousands + hundreds)) {
-                    if (digit_diff < LINE_NUMBER_TOGGLE_LENGTH * (thousands + 1)) {
-                        new_status_color(BLACK);
-                    } else {
-                        new_status_color(HUNDREDS);
-                    }
-                } else if (digit_diff < LINE_NUMBER_TOGGLE_LENGTH * (thousands + hundreds + tens)) {
-                    if (digit_diff < LINE_NUMBER_TOGGLE_LENGTH * (thousands + hundreds + 1)) {
-                        new_status_color(BLACK);
-                    } else {
-                        new_status_color(TENS);
-                    }
-                } else {
-                    if (digit_diff < LINE_NUMBER_TOGGLE_LENGTH * (thousands + hundreds + tens + 1)) {
-                        new_status_color(BLACK);
-                    } else {
-                        new_status_color(ONES);
-                    }
-                }
-            } else {
-                new_status_color(BLACK);
-            }
-        }
-        #else
-        (void) found_main; // Pretend to use found_main so the compiler doesn't complain.
-        #endif
-    }
-}
-
-#ifdef UART_REPL
-struct usart_module usart_instance;
-#endif
-
-#ifdef ENABLE_MICRO_TRACE_BUFFER
-// Stores 2 ^ TRACE_BUFFER_MAGNITUDE_PACKETS packets.
-// 7 -> 128 packets
-#define TRACE_BUFFER_MAGNITUDE_PACKETS 7
-// Size in uint32_t. Two per packet.
-#define TRACE_BUFFER_SIZE (1 << (TRACE_BUFFER_MAGNITUDE_PACKETS + 1))
-// Size in bytes. 4 bytes per uint32_t.
-#define TRACE_BUFFER_SIZE_BYTES (TRACE_BUFFER_SIZE << 2)
-__attribute__((__aligned__(TRACE_BUFFER_SIZE_BYTES))) uint32_t mtb[TRACE_BUFFER_SIZE];
-#endif
-
-// Serial number as hex characters.
-char serial_number[USB_DEVICE_GET_SERIAL_NAME_LENGTH];
-void load_serial_number(void) {
-    char nibble_to_hex[16] = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A',
-        'B', 'C', 'D', 'E', 'F'};
-    uint32_t* addresses[4] = {(uint32_t *) 0x0080A00C, (uint32_t *) 0x0080A040,
-                              (uint32_t *) 0x0080A044, (uint32_t *) 0x0080A048};
-    for (int i = 0; i < 4; i++) {
-        for (int j = 0; j < 8; j++) {
-            uint8_t nibble = (*(addresses[i]) >> j * 4) & 0xf;
-            serial_number[i * 8 + j] = nibble_to_hex[nibble];
-        }
-    }
-}
-
-// Provided by the linker;
-extern uint32_t _ezero;
-
-safe_mode_t samd21_init(void) {
-#ifdef ENABLE_MICRO_TRACE_BUFFER
-    REG_MTB_POSITION = ((uint32_t) (mtb - REG_MTB_BASE)) & 0xFFFFFFF8;
-    REG_MTB_FLOW = (((uint32_t) mtb - REG_MTB_BASE) + TRACE_BUFFER_SIZE_BYTES) & 0xFFFFFFF8;
-    REG_MTB_MASTER = 0x80000000 + (TRACE_BUFFER_MAGNITUDE_PACKETS - 1);
-#else
-    // Triple check that the MTB is off. Switching between debug and non-debug
-    // builds can leave it set over reset and wreak havok as a result.
-    REG_MTB_MASTER = 0x00000000 + 6;
-#endif
-
-// On power on start or external reset, set _ezero to the canary word. If it
-// gets killed, we boot in safe mod. _ezero is the boundary between statically
-// allocated memory including the fixed MicroPython heap and the stack. If either
-// misbehaves, the canary will not be in tact after soft reset.
-#ifdef CIRCUITPY_CANARY_WORD
-    if (PM->RCAUSE.bit.POR == 1 || PM->RCAUSE.bit.EXT == 1) {
-        _ezero = CIRCUITPY_CANARY_WORD;
-    } else if (PM->RCAUSE.bit.SYST == 1) {
-        // If we're starting from a system reset we're likely coming from the
-        // bootloader or hard fault handler. If we're coming from the handler
-        // the canary will be CIRCUITPY_SAFE_RESTART_WORD and we don't want to
-        // revive the canary so that a second hard fault won't restart. Resets
-        // from anywhere else are ok.
-        if (_ezero == CIRCUITPY_SAFE_RESTART_WORD) {
-            _ezero = ~CIRCUITPY_CANARY_WORD;
-        } else {
-            _ezero = CIRCUITPY_CANARY_WORD;
-        }
-    }
-#endif
-
-    load_serial_number();
-
-    irq_initialize_vectors();
-    cpu_irq_enable();
-
-    // Initialize the sleep manager
-    sleepmgr_init();
-
-    uint16_t dfll_fine_calibration = 0x1ff;
-#ifdef CALIBRATE_CRYSTALLESS
-    // This is stored in an NVM page after the text and data storage but before
-    // the optional file system. The first 16 bytes are the identifier for the
-    // section.
-    if (strcmp((char*) INTERNAL_CIRCUITPY_CONFIG_START_ADDR, "CIRCUITPYTHON1") == 0) {
-        dfll_fine_calibration = ((uint16_t *) INTERNAL_CIRCUITPY_CONFIG_START_ADDR)[8];
-    }
-#endif
-
-    // We pass in the DFLL fine calibration because we can't change it once the
-    // clock is going.
-    system_init(dfll_fine_calibration);
-
-    delay_init();
-
-    board_init();
-
-    // Configure millisecond timer initialization.
-    tick_init();
-
-    // Uncomment to init PIN_PA17 for debugging.
-    // struct port_config pin_conf;
-    // port_get_config_defaults(&pin_conf);
-    //
-    // pin_conf.direction  = PORT_PIN_DIR_OUTPUT;
-    // port_pin_set_config(MICROPY_HW_LED1, &pin_conf);
-    // port_pin_set_output_level(MICROPY_HW_LED1, false);
-
-    rgb_led_status_init();
-
-    // Init the nvm controller.
-    struct nvm_config config_nvm;
-    nvm_get_config_defaults(&config_nvm);
-    config_nvm.manual_page_write = false;
-    nvm_set_config(&config_nvm);
-
-    init_shared_dma();
-
-    #ifdef CIRCUITPY_CANARY_WORD
-    // Run in safe mode if the canary is corrupt.
-    if (_ezero != CIRCUITPY_CANARY_WORD) {
-        return HARD_CRASH;
-    }
-    #endif
-
-    if (PM->RCAUSE.bit.BOD33 == 1 || PM->RCAUSE.bit.BOD12 == 1) {
-        return BROWNOUT;
-    }
-
-    if (board_requests_safe_mode()) {
-        return USER_SAFE_MODE;
-    }
-
-    #if CIRCUITPY_INTERNAL_NVM_SIZE > 0
-    // Upgrade the nvm flash to include one sector for eeprom emulation.
-    struct nvm_fusebits fuses;
-    if (nvm_get_fuses(&fuses) == STATUS_OK &&
-            fuses.eeprom_size == NVM_EEPROM_EMULATOR_SIZE_0) {
-        #ifdef INTERNAL_FLASH_FS
-        // Shift the internal file system up one row.
-        for (uint8_t row = 0; row < TOTAL_INTERNAL_FLASH_SIZE / NVMCTRL_ROW_SIZE; row++) {
-            uint32_t new_row_address = INTERNAL_FLASH_MEM_SEG1_START_ADDR + row * NVMCTRL_ROW_SIZE;
-            nvm_erase_row(new_row_address);
-            nvm_write_buffer(new_row_address,
-                             (uint8_t*) (new_row_address + CIRCUITPY_INTERNAL_EEPROM_SIZE),
-                             NVMCTRL_ROW_SIZE);
-        }
-        #endif
-        uint32_t nvm_size = CIRCUITPY_INTERNAL_NVM_SIZE;
-        uint8_t enum_value = 6;
-        while (nvm_size > 256 && enum_value != 255) {
-            nvm_size /= 2;
-            enum_value -= 1;
-        }
-        if (enum_value != 255 && nvm_size == 256) {
-            // Mark the last section as eeprom now.
-            fuses.eeprom_size = (enum nvm_eeprom_emulator_size) enum_value;
-            nvm_set_fuses(&fuses);
-        }
-    }
-    #endif
-
-    return NO_SAFE_MODE;
-}
-
-extern uint32_t _estack;
-extern uint32_t _ebss;
-
-int main(void) {
-    // initialise the cpu and peripherals
-    safe_mode_t safe_mode = samd21_init();
-
-    // Stack limit should be less than real stack size, so we have a chance
-    // to recover from limit hit.  (Limit is measured in bytes.)
-    mp_stack_ctrl_init();
-    mp_stack_set_limit((char*)&_estack - (char*)&_ebss - 1024);
-
-
-#if MICROPY_MAX_STACK_USAGE
-    // _ezero (same as _ebss) is an int, so start 4 bytes above it.
-    mp_stack_set_bottom(&_ezero + 1);
-    mp_stack_fill_with_sentinel();
-#endif
-
-    init_flash_fs();
-
-    // Reset everything and prep MicroPython to run boot.py.
-    reset_samd21();
-    reset_board();
-    reset_mp();
-
-    // Turn on autoreload by default but before boot.py in case it wants to change it.
-    autoreload_enable();
-
-    // By default our internal flash is readonly to local python code and
-    // writeable over USB. Set it here so that boot.py can change it.
-    flash_set_usb_writeable(true);
-
-    // If not in safe mode, run boot before initing USB and capture output in a
-    // file.
-    if (safe_mode == NO_SAFE_MODE && MP_STATE_VM(vfs_mount_table) != NULL) {
-        new_status_color(BOOT_RUNNING);
-        #ifdef CIRCUITPY_BOOT_OUTPUT_FILE
-        // Since USB isn't up yet we can cheat and let ourselves write the boot
-        // output file.
-        flash_set_usb_writeable(false);
-        FIL file_pointer;
-        boot_output_file = &file_pointer;
-        f_open(&((fs_user_mount_t *) MP_STATE_VM(vfs_mount_table)->obj)->fatfs,
-            boot_output_file, CIRCUITPY_BOOT_OUTPUT_FILE, FA_WRITE | FA_CREATE_ALWAYS);
-        flash_set_usb_writeable(true);
-        #endif
-
-        // TODO(tannewt): Re-add support for flashing boot error output.
-        bool found_boot = maybe_run("settings.txt", NULL) ||
-                          maybe_run("settings.py", NULL) ||
-                          maybe_run("boot.py", NULL) ||
-                          maybe_run("boot.txt", NULL);
-        (void) found_boot;
-
-        #ifdef CIRCUITPY_BOOT_OUTPUT_FILE
-        f_close(boot_output_file);
-        flash_flush();
-        boot_output_file = NULL;
-        #endif
-
-        // Reset to remove any state that boot.py setup. It should only be used to
-        // change internal state thats not in the heap.
-        reset_samd21();
-        reset_mp();
-    }
-
-    usb_hid_init();
-
-    // Start USB after getting everything going.
-    #ifdef USB_REPL
-        udc_start();
-    #endif
-
-    // Boot script is finished, so now go into REPL/main mode.
-    int exit_code = PYEXEC_FORCED_EXIT;
-    bool skip_repl = true;
-    bool first_run = true;
-    for (;;) {
-        if (!skip_repl) {
-            // The REPL mode can change, or it can request a reload.
-            bool autoreload_on = autoreload_is_enabled();
-            autoreload_disable();
-            new_status_color(REPL_RUNNING);
-            if (pyexec_mode_kind == PYEXEC_MODE_RAW_REPL) {
-                exit_code = pyexec_raw_repl();
-            } else {
-                exit_code = pyexec_friendly_repl();
-            }
-            if (autoreload_on) {
-                autoreload_enable();
-            }
-            reset_samd21();
-            reset_board();
-            reset_mp();
-        }
-        if (exit_code == PYEXEC_FORCED_EXIT) {
-            if (!first_run) {
-                mp_hal_stdout_tx_str("soft reboot\r\n");
-            }
-            first_run = false;
-            skip_repl = start_mp(safe_mode);
-            reset_samd21();
-            reset_board();
-            reset_mp();
-        } else if (exit_code != 0) {
-            break;
-        }
-    }
-    mp_deinit();
-    return 0;
-}
-
-void gc_collect(void) {
-    // WARNING: This gc_collect implementation doesn't try to get root
-    // pointers from CPU registers, and thus may function incorrectly.
-    void *dummy;
-    gc_collect_start();
-    // This collects root pointers from the VFS mount table. Some of them may
-    // have lost their references in the VM even though they are mounted.
-    gc_collect_root((void**)&MP_STATE_VM(vfs_mount_table), sizeof(mp_vfs_mount_t) / sizeof(mp_uint_t));
-    // This naively collects all object references from an approximate stack
-    // range.
-    gc_collect_root(&dummy, ((mp_uint_t)&_estack - (mp_uint_t)&dummy) / sizeof(mp_uint_t));
-    gc_collect_end();
-}
-
-void NORETURN nlr_jump_fail(void *val) {
-    HardFault_Handler();
-    while (true) {}
-}
-
-void NORETURN __fatal_error(const char *msg) {
-    HardFault_Handler();
-    while (true) {}
-}
-
-#ifndef NDEBUG
-void MP_WEAK __assert_func(const char *file, int line, const char *func, const char *expr) {
-    printf("Assertion '%s' failed, at file %s:%d\n", expr, file, line);
-    __fatal_error("Assertion failed");
-}
-#endif