Entry at reset, C startup, user LED driven by System Tick on STM32F030F4.

blink.c

@@ -0,0 +1,45 @@
+/* blink.c -- user LED blink
+** Copyright (c) 2020 Renaud Fivet
+*/
+
+/* Memory locations defined by linker script */
+extern long __StackTop ;        /* &__StackTop points after end of stack */
+void Reset_Handler( void) ;     /* Entry point for execution */
+
+/* Interrupt vector table:
+ * 1  Stack Pointer reset value
+ * 15 System Exceptions
+ * NN Device specific Interrupts
+ */
+typedef void (*isr_p)( void) ;
+isr_p const isr_vector[ 2] __attribute__((section(".isr_vector"))) = {
+    (isr_p) &__StackTop,
+/* System Exceptions */
+    Reset_Handler
+} ;
+
+#define RCC                 ((volatile long *) 0x40021000)
+#define RCC_AHBENR          RCC[ 5]
+#define RCC_AHBENR_IOPBEN   0x00040000  /*  18: I/O port B clock enable */
+
+#define GPIOB               ((volatile long *) 0x48000400)
+#define GPIOB_MODER         GPIOB[ 0]
+#define GPIOB_ODR           GPIOB[ 5]
+
+void Reset_Handler( void) {
+    int delay ;
+
+/* User LED ON */
+    RCC_AHBENR |= RCC_AHBENR_IOPBEN ;   /* Enable IOPB periph */
+    GPIOB_MODER |= 1 << (1 * 2) ;       /* PB1 Output [01], over default 00 */
+    /* OTYPER Push-Pull by default */
+    /* PB1 output default LOW at reset */
+
+/* User LED blink */
+    for( ;;) {
+        for( delay = 1000000 ; delay ; delay--) ;   /* delay between toggling */
+        GPIOB_ODR ^= 1 << 1 ;                       /* toggle PB1 (User LED) */
+    }
+}
+
+/* end of blink.c */