pbio/drv/reset/reset_ev3: Implement software reset reason tracking

This helps determine whether the system was soft-rebooted,
booted from cold, or reset due to a crash.

Author: ArcaneNibble

lib/pbio/drv/reset/reset_ev3.c

@@ -7,6 +7,8 @@
 
 #if PBDRV_CONFIG_RESET_EV3
 
+#include <stdbool.h>
+
 #include <pbdrv/reset.h>
 #include <pbdrv/gpio.h>
 
@@ -19,6 +21,11 @@
 
 #define BOOTLOADER_UPDATE_MODE_VALUE    0x5555AAAA
 
+// 'Pybr'
+#define RESET_REASON_FLAG_WDT           0x50796272
+// 'rboo'
+#define RESET_REASON_FLAG_SOFT_RESET    0x72626f6f
+
 typedef struct {
     // 0xffff1ff0
     uint32_t _dummy0;
@@ -39,10 +46,13 @@ typedef struct {
 // This lives at the very end of the ARM local RAM.
 extern volatile persistent_data_t ev3_persistent_data;
 
+static uint32_t saved_reset_reason_flag;
+
 static const pbdrv_gpio_t poweroff_pin = PBDRV_GPIO_EV3_PIN(13, 19, 16, 6, 11);
 
 void pbdrv_reset_init(void) {
-    pbdrv_gpio_out_high(&poweroff_pin);
+    saved_reset_reason_flag = ev3_persistent_data.reset_reason_flag;
+    ev3_persistent_data.reset_reason_flag = RESET_REASON_FLAG_WDT;
 }
 
 void pbdrv_reset(pbdrv_reset_action_t action) {
@@ -57,6 +67,8 @@ void pbdrv_reset(pbdrv_reset_action_t action) {
             default:
                 // PBDRV_RESET_ACTION_RESET
 
+                ev3_persistent_data.reset_reason_flag = RESET_REASON_FLAG_SOFT_RESET;
+
                 // Poke the watchdog timer with a bad value to immediately trigger it
                 HWREG(SOC_TMR_1_REGS + TMR_WDTCR) = 0;
                 break;
@@ -65,9 +77,19 @@ void pbdrv_reset(pbdrv_reset_action_t action) {
 }
 
 pbdrv_reset_reason_t pbdrv_reset_get_reason(void) {
+    if (saved_reset_reason_flag == RESET_REASON_FLAG_SOFT_RESET) {
+        return PBDRV_RESET_REASON_SOFTWARE;
+    }
+    if (saved_reset_reason_flag == RESET_REASON_FLAG_WDT) {
+        return PBDRV_RESET_REASON_WATCHDOG;
+    }
     return PBDRV_RESET_REASON_NONE;
 }
 
+void pbdrv_reset_ev3_early_init(void) {
+    pbdrv_gpio_out_high(&poweroff_pin);
+}
+
 void pbdrv_reset_power_off(void) {
     pbdrv_gpio_out_low(&poweroff_pin);
 }

lib/pbio/drv/reset/reset_ev3.h

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2025 The Pybricks Authors
+
+// The EV3 requires a GPIO pin to be set in order to stay powered on.
+// We want to be able to do this as early as possible.
+
+#ifndef _INTERNAL_PBDRV_RESET_EV3_H_
+#define _INTERNAL_PBDRV_RESET_EV3_H_
+
+void pbdrv_reset_ev3_early_init(void);
+
+#endif // _INTERNAL_PBDRV_RESET_EV3_H_

lib/pbio/platform/ev3/platform.c

@@ -63,8 +63,8 @@
 #include "../../drv/led/led_dual.h"
 #include "../../drv/led/led_pwm.h"
 #include "../../drv/pwm/pwm_ev3.h"
+#include "../../drv/reset/reset_ev3.h"
 #include "../../drv/uart/uart_ev3.h"
-#include "../../drv/reset/reset.h"
 
 enum {
     LED_DEV_0_STATUS,
@@ -668,7 +668,7 @@ void SystemInit(void) {
 
     // Must set the power enable bin before disabling the pull up on the power
     // pin below, otherwise the hub will power off.
-    pbdrv_reset_init();
+    pbdrv_reset_ev3_early_init();
 
     // Disable all pull-up/pull-down groups.
     HWREG(SOC_SYSCFG_1_REGS + SYSCFG1_PUPD_ENA) &= ~0xFFFFFFFF;