kernel.c

   1 #include "link.h"
   2 #include "stm32f411.h"
   3
   4 const char msg[] = "blink ";
   5
   6 static void
   7 delay (void)
   8 {
   9   volatile unsigned int i;
  10   for (i = 0; i < 500000; i++);
  11 }
  12
  13 static void
  14 reset_handler (void)
  15 {
  16   unsigned int *src, *dst;
  17   unsigned int off;
  18
  19   /* relocate .data to sram  */
  20   src = &_data_lma_start;
  21   dst = &_data_vma_start;
  22
  23   while (dst < &_data_vma_end)
  24     *(dst++) = *(src++);
  25
  26   /* initialize .bss  */
  27   dst = &_bss_vma_start;
  28
  29   while (dst < &_bss_vma_end)
  30     *(dst++) = 0;
  31
  32   /* (todo) usart pin setup (alt func and enable port clock)  */
  33
  34   /* UE: USART enable  */
  35   *USART_CR1 |= (1u << 13); /* 1: USART enable  */
  36   /* M: Word length  */
  37   *USART_CR1 &= ~(1u << 12); /* 0: 1 Start bit, 8 Data bits, n Stop bit  */
  38   /* STOP: STOP bits  */
  39   *USART_CR2 &= ~(3u << 12); /* 00: 1 Stop bit  */
  40   /* the clock frequnecy is 16mhz initially, so for a baud rate of 115.2 KBps we
  41    * need to set USARTDIV=8.6875  */
  42   *USART_BRR = (8u << 4) | 11; /* mantissa and fraction (/16)  */
  43   /* TE: Transmitter enable  */
  44   *USART_CR1 |= (1u << 3); /* 1: Transmitter is enabled  */
  45
  46   /* blink blink setup  */
  47   *RCC_AHB1ENR |= (1u << 2);
  48   *GPIOC_MODER &= ~(3u << 26);
  49   *GPIOC_MODER |= (1u << 26);
  50
  51   while (1)
  52     {
  53       /* speak  */
  54       off = 0;
  55       do
  56         {
  57           /* TXE: Transmit data register empty  */
  58           if (!(*USART_SR & (1u << 7)))
  59             continue;
  60
  61           *USART_DR = msg[off++];
  62         }
  63       while (off < sizeof msg);
  64
  65       /* blink  */
  66       *GPIOC_ODR ^= (1u << 13);
  67       delay ();
  68     }
  69 }
  70
  71 __attribute__ ((section (".vector_table"), used))
  72 static unsigned long const vector_table[] = {
  73   (unsigned long) &_sram_end,
  74   (unsigned long) reset_handler,
  75 };