Proper entry point

boot/crt0.c

@@ -1,10 +1,10 @@
-typedef long uint32_t;
+typedef long uint32_t; //FIXME: Extrude this in another file, and assert it
 
 extern const void * _data_segment_start_flash;
 extern const void * _data_segment_start_ram;
 extern const void * _data_segment_end_ram;
 
-void reset(void);
+void _start(void);
 
 /* Interrupt Service Routines are void->void functions */
 typedef void(*ISR)(void);
@@ -21,16 +21,16 @@ ISR InitialisationVector[INITIALISATION_VECTOR_SIZE]
   __attribute__((section(".isr_vector_table")))
   = {
   0x20010000, //FIXME: This is the stack pointer!
-  reset,
+  _start,
   0,
   0,
   0
 };
 
-void blink(void);
+void main(int argc, char * argv[]);
 
-void reset(void) {
-  // This is where execution start after reset.
+void _start(void) {
+  // This is where execution starts after reset.
   // Many things are not initialized yet so the code here has to pay attention.
 
   /* Copy data segment to RAM
@@ -45,8 +45,5 @@ void reset(void) {
     *ramPointer++ = *flashPointer++;
   }
 
-  blink();
+  main(0, 0x0);
 }
-/*
-void _start(void) {
-}*/

boot/stm32f429_flash.ld

@@ -4,6 +4,10 @@ MEMORY {
   CCM (rwx)  : ORIGIN = 0x10000000, LENGTH = 64K
 }
 
+/* We want the code at symbol "reset" to be laid out at the beginning of the
+ * text section */
+ENTRY(_start)
+
 SECTIONS {
   .isr_vector_table ORIGIN(FLASH) : {
     /* We're explicitly asking for the ISR vector table to be at the beginning
@@ -16,6 +20,7 @@ SECTIONS {
      * vector should be set to indicate Thumb code */
   } >FLASH
 
+
   .text : {
     . = ALIGN(4);
     *(.text)

src/blinky.c

@@ -0,0 +1,84 @@
+long DataSectionTest = 0x1234;
+
+void sleep(long delay);
+
+int main(int argc, char * argv[]) {
+  for (int i=0; i< DataSectionTest; i++) {
+  }
+
+  // We want to blink LEDs connected to GPIO pin G13 and G14
+  // (this is documented in our board's PDF)
+  //
+  // GPIO are grouped by letter, and GPIO "G" live on the "AHB1" bus
+  // (this is documented in the STM32F4 reference mnual, page 65)
+
+  // More specifically, the boundary addresses for GPIOC are
+  // 0x4002 1800 - 0x4002 1BFF
+  //
+
+  // Step 1 : Enable clock in RCC_AHBxENR
+  // (RCC stands for "Reset and Clock Control)
+  // Per doc (STM32F4 reference manual, page 266), we want to enable
+  //  the 6th bit of RCC_AHB1ENR, which is at offset 0x30
+  // The RCC register boundary address is 0x4002 3800 - 0x4002 3BFF
+  // (per STM32F429xx datasheet)
+  // In other words, we want to enable bit 6 of (0x40023830)
+
+  long * RCCAHB1ENR = (long *)0x40023830;
+  *RCCAHB1ENR |= (1 << 6); // Set 6th bit of RCCAHB1ENR
+
+  // Step 2 : Configure the GPIO pin
+  // Set the mode to general purpose output
+  // GPIOG_MODER, bit 26 and 27 = pin13
+  // GPIOG_MODER, bit 28 and 29 = pin14
+  // A value of 0,0 for these two bits means input (reset state)
+  // and 0,1 for these two bits means output (which we want)
+  long * GPIOG_MODER = (long *)0x40021800; // GPIOC register
+
+  *GPIOG_MODER &= ~(1 << 27); // Clear bit 27 of GPIOG_MODER
+  *GPIOG_MODER |= (1 << 26); // Set bit 26 of RCCAHB1ENR
+
+  *GPIOG_MODER &= ~(1 << 29); // Clear bit 29 of GPIOG_MODER
+  *GPIOG_MODER |= (1 << 28); // Set bit 28 of RCCAHB1ENR
+
+  // Per doc, the output is push-pull by default (yay)
+  // And we should also set the output speed, but really
+  // we don't care (we're doing something super slow)
+
+  long delay = 10000;
+  long * GPIOG_PUPDR = (long *)(0x40021800 + 0xC); // Per doc, ref man page 283
+  long * GPIOG_ODR = (long *)(0x40021800 + 0x14); // per doc, data register of GPIO G
+
+  while (1) {
+    /*
+    // Pull-up pin 13
+    *GPIOG_PUPDR &= ~(1 << 27);
+    *GPIOG_PUPDR |= (1 << 26);
+    // Pull-up pin 14
+    *GPIOG_PUPDR &= ~(1 << 29);
+    *GPIOG_PUPDR |= (1 << 28);
+    */
+    *GPIOG_ODR = 0x2000;
+
+    sleep(100000);
+
+    *GPIOG_ODR = 0x4000;
+
+    /*
+    // Pull-down pin 13
+    *GPIOG_PUPDR &= ~(1 << 26);
+    *GPIOG_PUPDR |= (1 << 27);
+    // Pull-down pin 14
+    *GPIOG_PUPDR &= ~(1 << 28);
+    *GPIOG_PUPDR |= (1 << 29);
+    */
+
+    sleep(100000);
+  }
+}
+
+void sleep(long delay) {
+  for (long i=0; i<delay; i++) {
+    // Do nothing!
+  }
+}