Add boot command to jump to the bootloader

After much poking around, I finally figured out how to make this work!
The problem was that the ChibiOS initialization code had disabled
interrupts before the __early_init function was run, making the
bootloader not work despite my best intentions.  This was fixed by
enabling interrupts just before jumping to the bootloader.  This in turn
required changing to GNU-flavored C11 to include an inline assembly
instruction.

Makefile

 
 # C specific options here (added to USE_OPT).
 ifeq ($(USE_COPT),)
-  USE_COPT = -std=c11
+  USE_COPT = -std=gnu11
 endif
 
 # C++ specific options here (added to USE_OPT).

boards/PD_BUDDY_SINK/board.c

  * generator plugin. Do not edit manually.
  */
 
+#include "stm32f072_bootloader.h"
 #include "hal.h"
 
 #if HAL_USE_PAL || defined(__DOXYGEN__)
 void __early_init(void) {
 
   stm32_clock_init();
+  /* Jump to the bootloader if the magic value is set in
+   * dfu_reset_to_bootloader_magic. */
+  if (dfu_reset_to_bootloader_magic == RESET_TO_BOOTLOADER_MAGIC_CODE) {
+    asm("cpsie i");
+    void (*bootloader)(void) = (void (*)(void)) (*((uint32_t *) SYSMEM_RESET_VECTOR));
+    dfu_reset_to_bootloader_magic = 0;
+    __set_MSP(BOOTLOADER_STACK_POINTER);
+    bootloader();
+    while (42);
+  }
 }
 
 #if HAL_USE_MMC_SPI || defined(__DOXYGEN__)

boards/PD_BUDDY_SINK/board.h

 /*
  * PD Buddy - USB Power Delivery for everyone
- * Copyright (C) 2017 Clayton G. Hobbs <clay@lakeserv.net>
+ * Copyright (C) 2017-2018 Clayton G. Hobbs <clay@lakeserv.net>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by

boards/PD_BUDDY_SINK/board.mk

 BOARDSRC = $(CHIBIOS)/../boards/PD_BUDDY_SINK/board.c
 
 # Required include directories
-BOARDINC = $(CHIBIOS)/../boards/PD_BUDDY_SINK
+BOARDINC = $(CHIBIOS)/../boards/PD_BUDDY_SINK $(CHIBIOS)/../src

boards/PD_BUDDY_SINK/cfg/board.chcfg

   </configuration_settings>
   <board_name>PD Buddy Sink</board_name>
   <board_id>PD_BUDDY_SINK</board_id>
-  <board_functions></board_functions>
+  <board_functions>
+  	<__early_init>/* Jump to the bootloader if the magic value is set in
+   * dfu_reset_to_bootloader_magic. */
+  if (dfu_reset_to_bootloader_magic == RESET_TO_BOOTLOADER_MAGIC_CODE) {
+    asm("cpsie i");
+    void (*bootloader)(void) = (void (*)(void)) (*((uint32_t *) SYSMEM_RESET_VECTOR));
+    dfu_reset_to_bootloader_magic = 0;
+    __set_MSP(BOOTLOADER_STACK_POINTER);
+    bootloader();
+    while (42);
+  }</__early_init></board_functions>
+  <headers>
+  	<header>stm32f072_bootloader.h</header></headers>
   <subtype>STM32F072xB</subtype>
   <clocks HSEFrequency="0" HSEBypass="true" LSEFrequency="0"
   	LSEBypass="false" LSEDrive="3 High Drive (default)" ></clocks>

src/shell.c

 #include "config.h"
 #include "led.h"
 #include "device_policy_manager.h"
+#include "stm32f072_bootloader.h"
 
 
 /* Buffer for unwritten configuration */
     chEvtSignal(pdbs_led_thread, PDBS_EVT_LED_IDENTIFY);
 }
 
+static void cmd_boot(BaseSequentialStream *chp, int argc, char *argv[])
+{
+    (void) argv;
+    if (argc > 0) {
+        chprintf(chp, "Usage: boot\r\n");
+        return;
+    }
+
+    sduStop(&SDU1);
+    usbDisconnectBus(serusbcfg.usbp);
+    dfu_run_bootloader();
+}
+
 static void cmd_get_cfg(BaseSequentialStream *chp, int argc, char *argv[])
 {
     struct pdbs_config *cfg = NULL;
 static const struct pdbs_shell_cmd commands[] = {
     {"license", cmd_license, "Show copyright and license information"},
     {"identify", cmd_identify, "Blink the LED to identify the device"},
+    {"boot", cmd_boot, "Run the DfuSe bootloader"},
     {"get_cfg", cmd_get_cfg, "Print the stored configuration"},
     {"load", cmd_load, "Load the stored configuration into the buffer"},
     {"write", cmd_write, "Store the configuration buffer"},

src/stm32f072_bootloader.c

+/*
+ * PD Buddy - USB Power Delivery for everyone
+ * Copyright (C) 2017-2018 Clayton G. Hobbs <clay@lakeserv.net>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "stm32f072_bootloader.h"
+
+
+uint32_t dfu_reset_to_bootloader_magic;
+
+
+void dfu_run_bootloader(void)
+{
+    dfu_reset_to_bootloader_magic = RESET_TO_BOOTLOADER_MAGIC_CODE;
+    NVIC_SystemReset();
+}

src/stm32f072_bootloader.h

+/*
+ * PD Buddy - USB Power Delivery for everyone
+ * Copyright (C) 2017-2018 Clayton G. Hobbs <clay@lakeserv.net>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef PDB_STM32F072_BOOTLOADER_H
+#define PDB_STM32F072_BOOTLOADER_H
+
+#include <stdint.h>
+
+#include <ch.h>
+
+/*
+ * Code to jump to the STM32F072 bootloader, based on
+ * https://stackoverflow.com/a/36793779
+ */
+
+#define SYSMEM_RESET_VECTOR 0x1FFFC804
+#define RESET_TO_BOOTLOADER_MAGIC_CODE 0xDEADBEEF
+#define BOOTLOADER_STACK_POINTER 0x20002250
+
+
+/* Magic value used for jumping to the STM32F072 bootloader */
+extern uint32_t dfu_reset_to_bootloader_magic;
+
+
+#endif /* PDB_STM32F072_BOOTLOADER_H */