#include "link.h"
#include "stm32f411.h"

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 line, off;

  /* Relocate .data section to SRAM  */
  src = &_data_lma_start;
  dst = &_data_vma_start;

  while (dst < &_data_vma_end)
    *(dst++) = *(src++);

  /* Initialize .bss section  */
  dst = &_bss_vma_start;

  while (dst < &_bss_vma_end)
    *(dst++) = 0;

  /*  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  */
  *USART1_CR1 |= (1u << 13); /* 1: USART enable  */
  /* M: Word length  */
  *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  */
  *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  */
  *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  */

  /*  Test UART and LED  ----------------------------------------------------  */

  while (1)
    {
      for (line = 0; line < sizeof text / sizeof *text; ++line)
        {
          /* 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  */

              /* DR[8:0]: Data value  */
              *USART1_DR = text[line][off++];
            }

          /* TC: Transmission complete  */
          while (!(*USART1_SR & (1u << 6))); /* 0: Transmission is not
                                                complete  */

          /* Blink LED  */
          *GPIOC_ODR ^= (1u << 13);
        }
    }
}

__attribute__ ((section (".vector_table"), used))
static unsigned long const vector_table[] = {
  (unsigned long) &_sram_end,
  (unsigned long) reset_handler,
};