[Bug] Essential Hub stuck after exiting DFU Mode without USB cable.

[laurensvalk]

Describe the bug
If you enter DFU mode on the Essential Hub but you forget to plug in USB, the hub won't turn on after you release the button.

You have to remove the battery first and try again. Then everything works normally.

Since this doesn't happen with the stock firmware, this is probably not a bug in the bootloader as we initially thought.

So we may be able to fix it in the firmware.

To reproduce
Steps to reproduce the behavior:

1. Press and hold the button until the link blinks pink.
2. Release the button.

Expected behavior
Boot Pybricks normally, just like it normally boots the stock firmware if that is installed.

[laurensvalk]

This partially fixes it:

diff --git a/lib/pbio/platform/essential_hub/platform.c b/lib/pbio/platform/essential_hub/platform.c
index 117da2f2..589c7a88 100644
--- a/lib/pbio/platform/essential_hub/platform.c
+++ b/lib/pbio/platform/essential_hub/platform.c
@@ -692,6 +692,15 @@ void SystemInit(void) {
     // since the firmware starts at 0x08008000, we need to set the vector table offset
     SCB->VTOR = (uint32_t)&_fw_isr_vector_src;
 
+    // Keep main power on (PB1)
+    RCC->AHB1ENR |= RCC_AHB1ENR_GPIOBEN;
+    GPIO_InitTypeDef gpio_init = {
+        .Pin = GPIO_PIN_1,
+        .Mode = GPIO_MODE_OUTPUT_PP,
+    };
+    HAL_GPIO_Init(GPIOB, &gpio_init);
+    HAL_GPIO_WritePin(GPIOB, GPIO_PIN_1, GPIO_PIN_SET);
+
     // bootloader disables interrupts
     __enable_irq();
 
@@ -722,19 +731,11 @@ void SystemInit(void) {
     HAL_RCC_ClockConfig(&clk_init, FLASH_LATENCY_5);
 
     // enable clocks
-    RCC->AHB1ENR |= RCC_AHB1ENR_GPIOAEN | RCC_AHB1ENR_GPIOBEN | RCC_AHB1ENR_GPIOCEN |
+    RCC->AHB1ENR |= RCC_AHB1ENR_GPIOAEN | RCC_AHB1ENR_GPIOCEN |
         RCC_AHB1ENR_GPIODEN | RCC_AHB1ENR_DMA1EN | RCC_AHB1ENR_DMA2EN;
     RCC->APB1ENR |= RCC_APB1ENR_USART2EN | RCC_APB1ENR_USART3EN | RCC_APB1ENR_UART5EN |
         RCC_APB1ENR_TIM2EN | RCC_APB1ENR_TIM3EN | RCC_APB1ENR_TIM4EN |
         RCC_APB1ENR_I2C3EN | RCC_APB1ENR_FMPI2C1EN | RCC_APB1ENR_SPI2EN;
     RCC->APB2ENR |= RCC_APB2ENR_TIM8EN | RCC_APB2ENR_ADC1EN | RCC_APB2ENR_SYSCFGEN;
     RCC->AHB2ENR |= RCC_AHB2ENR_OTGFSEN;
-
-    // Keep main power on (PB1)
-    GPIO_InitTypeDef gpio_init = {
-        .Pin = GPIO_PIN_1,
-        .Mode = GPIO_MODE_OUTPUT_PP,
-    };
-    HAL_GPIO_Init(GPIOB, &gpio_init);
-    HAL_GPIO_WritePin(GPIOB, GPIO_PIN_1, GPIO_PIN_SET);
 }

But it is only fixed if you reboot after just installing the firmware. If you remove the batteries at least once, then it isn't fixed.

[laurensvalk]

Actually, maybe this is just coincidental.