at32: Artery MCU does not have backup regs in the STM32 location

Hence the firmware-update flag simply did not work. Instead copy the
flag-in-ram approach already used by the AT32F435 build. Keep the
flag-in-bkp approach only for STM32F105, and only for compatibility
with old versions of the update bootloader.

Author: keirf

inc/mcu/at32f435.h

@@ -66,9 +66,6 @@ void gpio_set_af(GPIO gpio, unsigned int pin, unsigned int af);
 #define SOFTIRQ_0 85
 #define SOFTIRQ_1 86
 
-extern volatile uint32_t _reset_flag;
-#define RESET_FLAG_BOOTLOADER 0xdeadbeefu
-
 /*
  * Local variables:
  * mode: C

inc/util.h

@@ -187,6 +187,10 @@ extern const char fw_ver[];
 extern const char build_date[];
 extern const char build_time[];
 
+/* Bootloader mode flag. */
+extern volatile uint32_t _reset_flag;
+#define RESET_FLAG_BOOTLOADER 0xdeadbeefu
+
 /* Text/data/BSS address ranges. */
 extern char _stext[], _etext[];
 extern char _smaintext[], _emaintext[];

scripts/stm32.ld.S

@@ -24,12 +24,10 @@ SECTIONS
     _etext = .;
   } >FLASH
 
-#if MCU == MCU_at32f435
   .flags : {
     _reset_flag = .;
     . = . + 4;
   } >RAM
-#endif
 
   .data : AT (_etext) {
     . = ALIGN(4);

src/fw_update.c

@@ -93,29 +93,33 @@ static bool_t main_fw_requested(void)
 
 static bool_t fw_update_requested(void)
 {
-    bool_t requested;
+    bool_t requested = FALSE;
 
 #if MCU == MCU_stm32f105
 
-    /* Power up the backup-register interface and allow writes. */
-    rcc->apb1enr |= RCC_APB1ENR_PWREN | RCC_APB1ENR_BKPEN;
-    pwr->cr |= PWR_CR_DBP;
+    /* We detect an Artery MCU by presence of Cortex-M4 CPUID. 
+     * Cortex-M4: 41xfc24x ; Cortex-M3: 41xfc23x */
+    is_artery_mcu = ((scb->cpuid >> 4) & 0xf) == 4;
 
-    /* Has bootloader been requested via magic numbers in the backup regs? */
-    requested = ((bkp->dr1[0] == 0xdead) && (bkp->dr1[1] == 0xbeef));
+    if (!is_artery_mcu) {
+        /* Power up the backup-register interface and allow writes. */
+        rcc->apb1enr |= RCC_APB1ENR_PWREN | RCC_APB1ENR_BKPEN;
+        pwr->cr |= PWR_CR_DBP;
 
-    /* Clean up backup registers and peripheral clocks. */
-    bkp->dr1[0] = bkp->dr1[1] = 0;
-    rcc->apb1enr = 0;
+        /* Has bootloader been requested via magic in the backup regs? */
+        requested |= ((bkp->dr1[0] == 0xdead) && (bkp->dr1[1] == 0xbeef));
 
-#elif MCU == MCU_at32f435
+        /* Clean up backup registers and peripheral clocks. */
+        bkp->dr1[0] = bkp->dr1[1] = 0;
+        rcc->apb1enr = 0;
+    }
+
+#endif
 
     /* Check-and-clear a magic value poked into SRAM1 by the main firmware. */
-    requested = (_reset_flag == RESET_FLAG_BOOTLOADER);
+    requested |= (_reset_flag == RESET_FLAG_BOOTLOADER);
     _reset_flag = 0;
 
-#endif
-
     return requested;
 }
 

src/main.c

@@ -2891,21 +2891,19 @@ static void factory_reset(void)
 static void update_firmware(void)
 {
 #if MCU == MCU_stm32f105
+    if (!is_artery_mcu) {
+        /* Power up the backup-register interface and allow writes. */
+        rcc->apb1enr |= RCC_APB1ENR_PWREN | RCC_APB1ENR_BKPEN;
+        pwr->cr |= PWR_CR_DBP;
 
-    /* Power up the backup-register interface and allow writes. */
-    rcc->apb1enr |= RCC_APB1ENR_PWREN | RCC_APB1ENR_BKPEN;
-    pwr->cr |= PWR_CR_DBP;
-
-    /* Indicate to bootloader that we want to perform firmware update. */
-    bkp->dr1[0] = 0xdead;
-    bkp->dr1[1] = 0xbeef;
-
-#elif MCU == MCU_at32f435
+        /* Indicate to bootloader that we want to perform firmware update. */
+        bkp->dr1[0] = 0xdead;
+        bkp->dr1[1] = 0xbeef;
+    }
+#endif
 
     _reset_flag = RESET_FLAG_BOOTLOADER;
 
-#endif
-
     system_reset();
 }