X-Git-Url: https://git.wirehaze.ovh/stm32f411ceu6.git/blobdiff_plain/607ec341be2feb79b7402498ddaf3a13f03d17a8..39b92fc9ae2523ffc74c8b19f4213bb83f41d331:/kernel.c?ds=inline

diff --git a/kernel.c b/kernel.c
index 6f66e49..dc4c134 100644
--- a/kernel.c
+++ b/kernel.c
@@ -1,70 +1,121 @@
 #include "link.h"
 #include "stm32f411.h"
 
-const char msg[] = "blink ";
-
-static void
-delay (void)
-{
-  volatile unsigned int i;
-  for (i = 0; i < 500000; i++);
-}
+static const char *text[] = {
+  "hello, friend.\r\n",
+  "hello, friend?\r\n",
+  "that's lame.\r\n",
+  "maybe i should give you a name.\r\n",
+  "but that's a slippery slope.\r\n",
+  "you're only in my head.\r\n",
+  "we have to remember that.\r\n",
+  "shit.\r\n",
+  "it's actually happening, i'm talking to an imaginary person.\r\n\n"
+};
 
 static void
 reset_handler (void)
 {
   unsigned int *src, *dst;
-  unsigned int off;
+  unsigned int line, off;
 
-  /* relocate .data to sram  */
+  /* Relocate .data section to SRAM  */
   src = &_data_lma_start;
   dst = &_data_vma_start;
 
   while (dst < &_data_vma_end)
     *(dst++) = *(src++);
 
-  /* initialize .bss  */
+  /* Initialize .bss section  */
   dst = &_bss_vma_start;
 
   while (dst < &_bss_vma_end)
     *(dst++) = 0;
 
-  /* (todo) usart pin setup (alt func and enable port clock)  */
+  /*  SYSCLK setup  ---------------------------------------------------------  */
+
+  /* HSEBYP: HSE clock bypass  */
+  *RCC_CR &= ~(1u << 18); /* 0: HSE oscillator not bypassed  */
+  /* HSEON: HSE clock enable  */
+  *RCC_CR |= (1u << 16); /* 1: HSE oscillator ON  */
+  /* HSERDY: HSE clock ready flag  */
+  while (!(*RCC_CR & (1u << 17))); /* 0: HSE oscillator not ready  */
+  /* SW: System clock switch  */
+  *RCC_CFGR &= ~(0b11u); /* Clear SW bits  */
+  *RCC_CFGR |= (0b01u); /* 01: HSE oscillator selected as system clock  */
+  /* SWS: System clock switch status  */
+  while ((*RCC_CFGR & (0b11u << 2)) != (0b01u << 2)); /* 01: HSE oscillator used
+                                                         as the system clock  */
+  /* HSION: Internal high-speed clock enable  */
+  *RCC_CR &= ~(1u); /* 0: HSI oscillator OFF  */
+
+  /*  UART setup  -----------------------------------------------------------  */
+
+  /* GPIOAEN: IO port A clock enable  */
+  *RCC_AHB1ENR |= (1u); /* 1: IO port A clock enabled  */
+  /* MODERy[1:0]: Port x configuration bits (y = 0..15)  */
+  *GPIOA_MODER &= ~(0b1111u << 18); /* Clear PA9 and PA10 bits  */
+  *GPIOA_MODER |= (0b1010u << 18); /* 10: Alternate function mode  */
+  /* AFRHy: Alternate function selection for port x bit y (y = 8..15)  */
+  *GPIOA_AFRH &= ~(0b11111111u << 4); /* Clear PA9 and PA10 bits  */
+  *GPIOA_AFRH |= (0b01110111u << 4); /* 0111: AF7  */
 
+  /* PA9: USART1_TX
+   * PA10: USART1_RX  */
+
+  /* USART1EN: USART1 clock enable  */
+  *RCC_APB2ENR |= (1u << 4); /* 1: USART1 clock enabled  */
   /* UE: USART enable  */
-  *USART_CR1 |= (1u << 13); /* 1: USART enable  */
+  *USART1_CR1 |= (1u << 13); /* 1: USART enable  */
   /* M: Word length  */
-  *USART_CR1 &= ~(1u << 12); /* 0: 1 Start bit, 8 Data bits, n Stop bit  */
+  *USART1_CR1 &= ~(1u << 12); /* 0: 1 Start bit, 8 Data bits, n Stop bit  */
+  /* PCE: Parity control enable  */
+  *USART1_CR1 &= ~(1u << 10); /* 0: Parity control disabled  */
   /* 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)  */
+  *USART1_CR2 &= ~(0b11u << 12); /* 00: 1 Stop bit  */
+  /* Clock frequency: 25MHz
+   * Desired baud rate: 1.2 KBps
+   * USARTDIV = 1302.0625  */
+  *USART1_BRR = (1302u << 4) | 1u; /* mantissa and fraction (/16)  */
   /* TE: Transmitter enable  */
-  *USART_CR1 |= (1u << 3); /* 1: Transmitter is enabled  */
+  *USART1_CR1 |= (1u << 3); /* 1: Transmitter is enabled  */
+
+  /*  LED setup  ------------------------------------------------------------  */
+
+  /* GPIOCEN: IO port C clock enable  */
+  *RCC_AHB1ENR |= (1u << 2); /* 1: IO port C clock enabled  */
+  /* MODERy[1:0]: Port x configuration bits (y = 0..15)  */
+  *GPIOC_MODER &= ~(0b11u << 26); /* Clear PC13 bits  */
+  *GPIOC_MODER |= (1u << 26); /* 01: General purpose output mode  */
+
+  /* PC13: 0 = LED on
+   *       1 = LED off  */
 
-  /* blink blink setup  */
-  *RCC_AHB1ENR |= (1u << 2);
-  *GPIOC_MODER &= ~(3u << 26);
-  *GPIOC_MODER |= (1u << 26);
+  /*  Test UART and LED  ----------------------------------------------------  */
 
   while (1)
     {
-      /* speak  */
-      off = 0;
-      do
+      for (line = 0; line < sizeof text / sizeof *text; ++line)
         {
-          /* TXE: Transmit data register empty  */
-          if (!(*USART_SR & (1u << 7)))
-            continue;
+          /* Print current line  */
+          off = 0;
+          while (text[line][off])
+            {
+              /* TXE: Transmit data register empty  */
+              while (!(*USART1_SR & (1u << 7))); /* 0: Data is not transferred
+                                                    to the shift register  */
 
-          *USART_DR = msg[off++];
-        }
-      while (off < sizeof msg);
+              /* DR[8:0]: Data value  */
+              *USART1_DR = text[line][off++];
+            }
+
+          /* TC: Transmission complete  */
+          while (!(*USART1_SR & (1u << 6))); /* 0: Transmission is not
+                                                complete  */
 
-      /* blink  */
-      *GPIOC_ODR ^= (1u << 13);
-      delay ();
+          /* Blink LED  */
+          *GPIOC_ODR ^= (1u << 13);
+        }
     }
 }