#tinygpmp: tinkering with STM32

tinygpmp/BLINK_WKG.c

@@ -0,0 +1,44 @@
+// This is the symbol defined in the linker script.
+extern unsigned long _end_of_ram;
+
+// We'll implement main a bit further down but we need the symbol for
+// the initial program counter / start address.
+void main();
+
+// This is our interrupt vector table that goes in the dedicated section.
+__attribute__ ((section(".interrupt_vectors"), used))
+void (* const interrupt_vectors[])(void) = {
+    // The first 32bit value is actually the initial stack pointer.
+    // We have to cast it to a function pointer since the rest of the array
+    // would all be function pointers to interrupt handlers.
+    (void (*)(void))((unsigned long)&_end_of_ram),
+
+    // The second 32bit value is the initial program counter aka. the
+    // function you want to run first.
+    main
+};
+
+void wait() {
+    // Do some NOPs for a while to pass some time.
+    for (unsigned int i = 0; i < 2000000; ++i) __asm__ volatile ("nop");
+}
+
+void main() {
+    // Enable port C clock gate.
+    *((volatile unsigned int *)0x40021018) |= (1 << 4);
+
+    // Configure GPIO C pin 13 as output.
+    *((volatile unsigned int *)0x40011004) = ((0x44444444 // The reset value
+        & ~(0xfU << 20))  // Clear out the bits for pin 13
+        |  (0x3U << 20)); // Set both MODE bits, leave CNF at 0
+
+    while (1) {
+        // Set the output bit.
+        *((volatile unsigned int *)0x40011010) = (1U << 13);
+        wait();
+        // Reset it again.
+        *((volatile unsigned int *)0x40011010) = (1U << 29);
+        wait();
+    }
+}
+