pbdrv/block_device: Implement async program load and save.

This replaces the polling SPI implementation (deactivated in the
previous commit) with asynchronous DMA driven SPI transfers.
This fixes motors going out of sync when starting programs.

Fixes pybricks/support#679

This also avoids touching file systems used by other known firmwares,
so that Pybricks can operate entirely stand alone. This reduces
the complexity of firmware installation and troubleshooting, because
there are no dependencies on prior firmwares or hub state.

It also lays the groundwork for saving and storing program data on
Powered Up hubs, but this isn't fully implemented in order to preserve
compatibility with Pybricks Code and the existing tutorial videos.

CHANGELOG.md

@@ -15,14 +15,30 @@
 ### Changed
 - Battery full indication (green light) comes on earlier ([support#647]).
 - New indication for over-charging battery (blinking green light).
+- On Move Hub, City Hub, and Technic Hub, programs can now be restarted with
+  the button after downloading them. After reboot, it still falls back to the
+  program stored in the firmware.
+- Improved program download process. Reduces the likelihood of getting errors
+  about incompatible .mpy files when accidentally entering characters in the
+  terminal window when no program is active.
+- On Prime Hub and Essential Hub, there is no longer a wait time after boot
+  before you can start programs.
+- On Prime Hub and Essential Hub, the user program is now stored in a section
+  of the external flash that is not used by any file system of other known
+  firmwares, in order to avoid compatibility issues when changing firmware.
 
 ### Fixed
+- Fixed motors going out of synch when starting program ([support#679]).
 - Fixed city hub turning back on after shutdown ([support#692]).
 - Fixed IMU I2C bus lockup on SPIKE hubs ([support#232]).
 - Fixed REPL history corrupt after soft reset ([support#699]).
+- Fixed "ValueError: incompatible .mpy file" when pressing the button when
+  there is no program yet ([support#599]).
 
 [support#232]: https://github.com/pybricks/support/issues/232
+[support#232]: https://github.com/pybricks/support/issues/599
 [support#647]: https://github.com/pybricks/support/issues/647
+[support#699]: https://github.com/pybricks/support/issues/679
 [support#692]: https://github.com/pybricks/support/issues/692
 [support#699]: https://github.com/pybricks/support/issues/699
 

bricks/stm32/stm32.mk

@@ -419,6 +419,8 @@ PBIO_SRC_C = $(addprefix lib/pbio/,\
 	drv/adc/adc_stm32_hal.c \
 	drv/adc/adc_stm32f0.c \
 	drv/battery/battery_adc.c \
+	drv/block_device/block_device_internal_flash_stm32.c \
+	drv/block_device/block_device_w25qxx_stm32.c \
 	drv/bluetooth/bluetooth_btstack_control_gpio.c \
 	drv/bluetooth/bluetooth_btstack_run_loop_contiki.c \
 	drv/bluetooth/bluetooth_btstack_uart_block_stm32_hal.c \

lib/pbio/drv/block_device/block_device.h

@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2022 The Pybricks Authors
+
+#ifndef _INTERNAL_PBDRV_BLOCK_DEVICE_H_
+#define _INTERNAL_PBDRV_BLOCK_DEVICE_H_
+
+#include <stdint.h>
+
+#include <pbdrv/config.h>
+#include <pbio/error.h>
+
+#if PBDRV_CONFIG_BLOCK_DEVICE
+
+void pbdrv_block_device_init(void);
+
+#else // PBDRV_CONFIG_BLOCK_DEVICE
+
+static inline void pbdrv_block_device_init(void) {
+}
+
+#endif // PBDRV_CONFIG_BLOCK_DEVICE
+
+#endif // _INTERNAL_PBDRV_BLOCK_DEVICE_H_

lib/pbio/drv/block_device/block_device_internal_flash_stm32.c

@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2022 The Pybricks Authors
+
+// Block device driver for Internal_flash.
+
+#include <pbdrv/config.h>
+
+#if PBDRV_CONFIG_BLOCK_DEVICE_INTERNAL_FLASH_STM32
+
+#include <stdint.h>
+#include <string.h>
+
+#include <contiki.h>
+
+#include "../core.h"
+
+#include <pbdrv/block_device.h>
+
+#include <pbio/error.h>
+#include <pbio/util.h>
+
+void pbdrv_block_device_init(void) {
+}
+
+void pbdrv_block_device_set_callback(void (*callback)(void)) {
+}
+
+PT_THREAD(block_device_read(struct pt *pt, uint32_t offset, uint8_t *buffer, uint32_t size, pbio_error_t *err)) {
+
+    PT_BEGIN(pt);
+
+    // TODO: Read from user flash. For now this just loads
+    // the mpy file appended to the firmware to keep Pybricks Code working.
+    extern uint32_t _pb_user_mpy_size;
+    if (_pb_user_mpy_size + 8 > pbdrv_block_device_get_size()) {
+        *err = PBIO_ERROR_FAILED;
+        PT_EXIT(pt);
+    }
+    extern uint8_t _pb_user_mpy_data[];
+    pbio_set_uint32_le(buffer, _pb_user_mpy_size + 8);
+    pbio_set_uint32_le(&buffer[4], _pb_user_mpy_size);
+    memcpy(&buffer[8], _pb_user_mpy_data, _pb_user_mpy_size);
+    *err = PBIO_SUCCESS;
+
+    PT_END(pt);
+}
+
+PT_THREAD(block_device_store(struct pt *pt, uint8_t *buffer, uint32_t size, pbio_error_t *err)) {
+
+    PT_BEGIN(pt);
+    // TODO: Implement saving to user flash.
+    *err = PBIO_ERROR_NOT_IMPLEMENTED;
+    PT_END(pt);
+}
+
+#endif // PBDRV_CONFIG_BLOCK_DEVICE_INTERNAL_FLASH_STM32