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

// 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 PL011_UART.
  wr32(PL011_UART_CR, 0);
  
  // Setup the GPIO pin 14 && 15.

  // Disable pull up/down for all GPIO pins & delay for 150 cycles.
  wr32(GPPUD, 0);
  delay(150);

  // Disable pull up/down for pin 14,15 & delay for 150 cycles.
  wr32(GPPUDCLK0, (1 << 14) | (1 << 15));
  delay(150);

  // Write 0 to GPPUDCLK0 to make it take effect.
  wr32(GPPUDCLK0, 0);

  // 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.
  wr32(PL011_UART_IBRD, 1);
  // Fractional part register = (.627 * 64) + 0.5 = 40.6 = ~40.
  wr32(PL011_UART_FBRD, 40);

  // Set 8 bit data transmission (1 stop bit, no parity)
  // and disable FIFO to be able to receive interrupt every received
  // char, not every 2 chars
  wr32(PL011_UART_LCRH, (1 << 5) | (1 << 6));

  // set interrupt to come when transmit FIFO becomes ≤ 1/8 full
  // or receive FIFO becomes ≥ 1/8 full
  // (not really matters, since we disabled FIFOs)
  wr32(PL011_UART_IFLS, 0);

  // Enable PL011_UART, receive & transfer part of UART.2
  wr32(PL011_UART_CR, (1 << 0) | (1 << 8) | (1 << 9));

  // At first, it's probably safer to disable interrupts :)
  uart_irq_disable();

  // The above disables the entire uart irq;
  // Also disable single sources within it
  wr32(PL011_UART_IMSC, 0);
}

inline static _Bool can_transmit(void)
{
  return !(rd32(PL011_UART_FR) & (1 << 5));
}

inline static _Bool can_receive(void)
{
  return !(rd32(PL011_UART_FR) & (1 << 4));
}

void putchar(char c)
{
  while (!can_transmit());
  
  wr32(PL011_UART_DR, c);
}

char getchar(void)
{
  while (!can_receive());
  
  return rd32(PL011_UART_DR);
}

_Bool putchar_non_blocking(char c)
{
  if (can_transmit())
    {
      wr32(PL011_UART_DR, c);
      return 0;
    }

  return 1;
}

int getchar_non_blocking(void)
{
  if (can_receive())
    return rd32(PL011_UART_DR);

  return -1;
}