Replace bootloader handoff

src/stm32f103/bluepill/DFU/DFU.c

@@ -16,12 +16,17 @@
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include "DFU/DFU.h"
+#include "backup.h"
+
 #include <libopencm3/cm3/scb.h>
 
-#include "DFU/DFU.h"
+/* Boot command for DAPBoot bootloader */
+static const uint32_t CMD_BOOT_VIA_DAPBOOT = 0x544F4F42UL;
 
+/* Writes a DFU command to the backup register and resets */
 void DFU_reset_and_jump_to_bootloader(void) {
-    /* Trigger the STLink/v2-1 bootloader via software reset */
+    backup_write(BKP0, CMD_BOOT_VIA_DAPBOOT);
     scb_reset_system();
     while (1);
 }

src/stm32f103/bluepill/DFU/backup.c

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2016, Devan Lai
+ *
+ * Permission to use, copy, modify, and/or distribute this software
+ * for any purpose with or without fee is hereby granted, provided
+ * that the above copyright notice and this permission notice
+ * appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+ * WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
+ * AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR
+ * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
+ * NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <libopencm3/stm32/rcc.h>
+#include <libopencm3/stm32/rtc.h>
+#include <libopencm3/stm32/pwr.h>
+
+#include "backup.h"
+
+#define RTC_BKP_DR(reg)  MMIO16(BACKUP_REGS_BASE + 4 + (4 * (reg)))
+
+void backup_write(enum BackupRegister reg, uint32_t value) {
+    rcc_periph_clock_enable(RCC_PWR);
+    rcc_periph_clock_enable(RCC_BKP);
+
+    pwr_disable_backup_domain_write_protect();
+    RTC_BKP_DR((int)reg*2) = value & 0xFFFFUL;
+    RTC_BKP_DR((int)reg*2+1) = (value & 0xFFFF0000UL) >> 16;
+    pwr_enable_backup_domain_write_protect();
+}
+
+uint32_t backup_read(enum BackupRegister reg) {
+    uint32_t value = ((uint32_t)RTC_BKP_DR((int)reg*2+1) << 16)
+                   | ((uint32_t)RTC_BKP_DR((int)reg*2) << 0);
+    return value;
+}

src/stm32f103/bluepill/DFU/backup.h

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2016, Devan Lai
+ *
+ * Permission to use, copy, modify, and/or distribute this software
+ * for any purpose with or without fee is hereby granted, provided
+ * that the above copyright notice and this permission notice
+ * appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+ * WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
+ * AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR
+ * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
+ * NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifndef BACKUP_H_INCLUDED
+#define BACKUP_H_INCLUDED
+
+#include <stdint.h>
+
+enum BackupRegister {
+    BKP0 = 0,
+    BKP1,
+    BKP2,
+    BKP3,
+    BKP4,
+};
+
+extern void backup_write(enum BackupRegister reg, uint32_t value);
+extern uint32_t backup_read(enum BackupRegister reg);
+
+#endif