Add shared emulator services, waveform generation and STM32 USB boot ports

c/set-protocol/ports/stm32g474-usb-boot/boot_request.c

@@ -0,0 +1,26 @@
+#include "boot_port.h"
+#include "stm32g4xx_hal.h"
+#define REQUEST_MAGIC 0x42555342UL
+static uint32_t reset_at;
+static bool reset_pending;
+static void backup_access(void)
+{
+    __HAL_RCC_PWR_CLK_ENABLE();
+    HAL_PWR_EnableBkUpAccess();
+    __HAL_RCC_RTCAPB_CLK_ENABLE();
+}
+bool g474_boot_requested(void)
+{
+    bool requested;
+    backup_access(); requested = TAMP->BKP0R == REQUEST_MAGIC;
+    TAMP->BKP0R = 0; return requested;
+}
+void g474_request_boot(uint32_t now)
+{
+    backup_access(); TAMP->BKP0R = REQUEST_MAGIC;
+    reset_at = now + 500; reset_pending = true;
+}
+void g474_reset_poll(uint32_t now)
+{
+    if (reset_pending && (int32_t)(now - reset_at) >= 0) NVIC_SystemReset();
+}