usart wip

[stm32f411ceu6.git] / kernel.c

diff --git a/kernel.c b/kernel.c
index 28d576d39c14642470c98d38824cd3621e75b100..6f66e49640c08b006a41bd93c87ce39135e5f692 100644 (file)
--- a/kernel.c
+++ b/kernel.c
@@ -1,13 +1,7 @@
-extern unsigned int _sram_end;
-extern unsigned int _data_vma_start;
-extern unsigned int _data_vma_end;
-extern unsigned int _data_lma_start;
-extern unsigned int _bss_vma_start;
-extern unsigned int _bss_vma_end;
+#include "link.h"
+#include "stm32f411.h"
 
-#define RCC_AHB1 ((volatile unsigned int * const) 0x40023830)
-#define GPIOC_MODER ((volatile unsigned int * const) 0x40020800)
-#define GPIOC_ODR ((volatile unsigned int * const) 0x40020814)
+const char msg[] = "blink ";
 
 static void
 delay (void)
@@ -20,6 +14,7 @@ static void
 reset_handler (void)
 {
   unsigned int *src, *dst;
+  unsigned int off;
 
   /* relocate .data to sram  */
   src = &_data_lma_start;
@@ -34,19 +29,46 @@ reset_handler (void)
   while (dst < &_bss_vma_end)
     *(dst++) = 0;
 
-  /* blink blink  */
-  *RCC_AHB1 |= (1u << 2);
+  /* (todo) usart pin setup (alt func and enable port clock)  */
+
+  /* UE: USART enable  */
+  *USART_CR1 |= (1u << 13); /* 1: USART enable  */
+  /* M: Word length  */
+  *USART_CR1 &= ~(1u << 12); /* 0: 1 Start bit, 8 Data bits, n Stop bit  */
+  /* STOP: STOP bits  */
+  *USART_CR2 &= ~(3u << 12); /* 00: 1 Stop bit  */
+  /* the clock frequnecy is 16mhz initially, so for a baud rate of 115.2 KBps we
+   * need to set USARTDIV=8.6875  */
+  *USART_BRR = (8u << 4) | 11; /* mantissa and fraction (/16)  */
+  /* TE: Transmitter enable  */
+  *USART_CR1 |= (1u << 3); /* 1: Transmitter is enabled  */
+
+  /* blink blink setup  */
+  *RCC_AHB1ENR |= (1u << 2);
   *GPIOC_MODER &= ~(3u << 26);
   *GPIOC_MODER |= (1u << 26);
 
   while (1)
     {
+      /* speak  */
+      off = 0;
+      do
+        {
+          /* TXE: Transmit data register empty  */
+          if (!(*USART_SR & (1u << 7)))
+            continue;
+
+          *USART_DR = msg[off++];
+        }
+      while (off < sizeof msg);
+
+      /* blink  */
       *GPIOC_ODR ^= (1u << 13);
       delay ();
     }
 }
 
-__attribute__ ((section (".vtbl"), used))
+__attribute__ ((section (".vector_table"), used))
 static unsigned long const vector_table[] = {
   (unsigned long) &_sram_end,
   (unsigned long) reset_handler,