1 files changed, 90 insertions, 0 deletions
diff --git a/src/blinky.c b/src/blinky.c
new file mode 100644
index 0000000..ca93df6
--- /dev/null
+++ b/src/blinky.c
@@ -0,0 +1,90 @@
+#include <stdint.h>
+
+/*
+ * Function (or really pointer to code) for the reset interrupt handler.
+ */
+void on_reset(void);
+
+/*
+ * Function which delays for a bit.
+ */
+void delay(void);
+
+/* Type def to a void function to make things mor ereadable. */
+typedef void (*isr_routine)(void);
+
+/* Gpio configuration structure. This is exactly how it is laid out in
+ * memory. In these registers bit X referes to pin X. */
+typedef struct {
+  /* The direction of the gpio pin. 1 = output, 0 = input. */
+  uint32_t dir;
+
+  /* The value of the gpio pin (for input). */
+  uint32_t in;
+
+  /* Write to set the output value for the pin. */
+  uint32_t out;
+
+  /* The clear value. Resets the pin to what it is at reset. */
+  uint32_t clr;
+
+  /* Sets the pin to be pull-up on logical 1 in input mode. */
+  uint32_t pu;
+
+  /* Sets whether the pin should be pull-down (open-drain) for logical 0 or
+   * drive for logical 1. 1 = pull-down, 0 = drive. */
+  uint32_t pd_drv;
+} gpio_t;
+
+/** The ISR Vector structure. This is linked to starting at address 0. */
+__attribute((__section__(".isr_vector"))) volatile struct {
+  // What NULL points to. nothing useful.
+  uint32_t reserved__;
+  // Called when the device boots or reset is pressed.
+  isr_routine reset_cb;
+  isr_routine nmi_cb;
+  isr_routine exc_cb;
+} isr_vectors = {.reset_cb = on_reset};
+
+// GPIO configuration registers. These are defined in the linker script.
+extern volatile gpio_t gpio_a;
+extern volatile gpio_t gpio_b;
+
+/* Main routine. This is called on_reset once everything else has been set up.
+ */
+static void start(void)
+{
+  uint32_t bit = 1 << 8;
+  gpio_a.dir |= bit;     // Set to "out"
+  gpio_a.pd_drv |= bit;  // Set to "open drain"
+
+  for (;;) {
+    gpio_a.out &= ~bit;  // Pin low (turns on LED)
+    delay();
+    gpio_a.out |= bit;  // Pin high (turns off LED)
+    delay();
+  }
+}
+
+/*
+ * The reset callback.This has to be a naked function because the stack pointer
+ * may not be initialized!!.
+ */
+__attribute((naked)) void on_reset(void)
+{
+  // Set up the stack pointer to point to the end of SRAM.
+  asm volatile(
+      "li	sp,0x20008000\n"
+      "addi	sp,sp,-4\n"
+      "jalr %0\n"
+      "spin:\n"
+      "j spin\n"
+      :
+      : "r"(start));
+}
+
+void delay(void)
+{
+  for (volatile uint32_t i = 0; i < 10000; ++i)
+    ;
+}