#include <stddef.h>
#include <stdint.h>
#include <uart.h>
#include <global.h>

// Memory-Mapped I/O output
static inline void mmio_write(uint32_t reg, uint32_t data)
{
  *(volatile uint32_t*)reg = data;
}

// Memory-Mapped I/O input
static inline uint32_t mmio_read(uint32_t reg)
{
  return *(volatile uint32_t*)reg;
}

// Loop <delay> times in a way that the compiler won't optimize away
static inline void delay(int32_t count)
{
  asm volatile("__delay_%=: subs %[count], %[count], #1; bne __delay_%=\n"
	       : "=r"(count): [count]"0"(count) : "cc");
}

void uart_init()
{
  // Disable UART0.
  mmio_write(UART0_CR, 0x00000000);
  // Setup the GPIO pin 14 && 15.

  // Disable pull up/down for all GPIO pins & delay for 150 cycles.
  mmio_write(GPPUD, 0x00000000);
  delay(150);

  // Disable pull up/down for pin 14,15 & delay for 150 cycles.
  mmio_write(GPPUDCLK0, (1 << 14) | (1 << 15));
  delay(150);

  // Write 0 to GPPUDCLK0 to make it take effect.
  mmio_write(GPPUDCLK0, 0x00000000);

  // Clear pending interrupts.
  mmio_write(UART0_ICR, 0x7FF);

  // Set integer & fractional part of baud rate.
  // Divider = UART_CLOCK/(16 * Baud)
  // Fraction part register = (Fractional part * 64) + 0.5
  // UART_CLOCK = 3000000; Baud = 115200.

  // Divider = 3000000 / (16 * 115200) = 1.627 = ~1.
  mmio_write(UART0_IBRD, 1);
  // Fractional part register = (.627 * 64) + 0.5 = 40.6 = ~40.
  mmio_write(UART0_FBRD, 40);

  // Enable FIFO & 8 bit data transmission (1 stop bit, no parity).
  mmio_write(UART0_LCRH, (1 << 4) | (1 << 5) | (1 << 6));

  // Mask all interrupts.
  mmio_write(UART0_IMSC, (1 << 1) | (1 << 4) | (1 << 5) | (1 << 6) |
	     (1 << 7) | (1 << 8) | (1 << 9) | (1 << 10));

  // Enable UART0, receive & transfer part of UART.
  mmio_write(UART0_CR, (1 << 0) | (1 << 8) | (1 << 9));
}

void uart_putc(unsigned char c)
{
  // Wait for UART to become ready to transmit.
  while ( mmio_read(UART0_FR) & (1 << 5) ) { }
  mmio_write(UART0_DR, c);
}

unsigned char uart_getc()
{
  // Wait for UART to have received something.
  while ( mmio_read(UART0_FR) & (1 << 4) ) { }
  return mmio_read(UART0_DR);
}

void uart_puts(const char* str)
{
  for (size_t i = 0; str[i] != '\0'; i ++)
    uart_putc((unsigned char)str[i]);
}