#include <libopencm3/stm32/usart.h>
#include <libopencm3/stm32/gpio.h>
#include <libopencm3/cm3/nvic.h>

#include "pinout.h"

#include "rs485.h"

#define RS485_BUFFER_SIZE 128
static volatile char debugBuffer[RS485_BUFFER_SIZE];

static volatile uint16_t readPos, writePos;
static volatile uint8_t bufferFull, bufferEmpty, usartActive;

void rs485_init(void)
{
	// initialize the ring buffer
	readPos = 0;
	writePos = 0;
	bufferFull = 0;
	bufferEmpty = 1;
	usartActive = 0;

	/* Initialize GPIOs */

	// RS485 drive enable signal
	gpio_clear(RS485_PORT, RS485_DE_PIN);
	gpio_mode_setup(RS485_PORT, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE, RS485_DE_PIN);

	// RX and TX pins
	gpio_mode_setup(RS485_PORT, GPIO_MODE_AF, GPIO_PUPD_NONE, RS485_TX_PIN | RS485_RX_PIN);
	gpio_set_af(RS485_PORT, GPIO_AF0, RS485_TX_PIN | RS485_RX_PIN);

	// enable interrupt
	nvic_enable_irq(NVIC_USART1_IRQ);

	/* Setup USART1 parameters. */
	usart_set_baudrate(USART1, 115200);
	usart_set_databits(USART1, 8);
	usart_set_stopbits(USART1, USART_CR2_STOPBITS_1);
	usart_set_mode(USART1, USART_MODE_TX);
	usart_set_parity(USART1, USART_PARITY_NONE);
	usart_set_flow_control(USART1, USART_FLOWCONTROL_NONE);

	/* Enable the USART. */
	usart_enable(USART1);

	/* Enable the USART1 TX Interrupt */
	usart_enable_tx_interrupt(USART1);
	usart_enable_tx_complete_interrupt(USART1);
}


static void rs485_transfer(void)
{
	if(bufferEmpty) {
		usart_disable_tx_interrupt(USART1);
		usartActive = 0;
		return;
	}

	usart_send(USART1, debugBuffer[readPos]);

	readPos++;
	if(readPos == RS485_BUFFER_SIZE) {
		readPos = 0;
	}

	if(readPos == writePos) {
		bufferEmpty = 1;
	}

	bufferFull = 0;
	usart_enable_tx_interrupt(USART1);
}


void usart1_isr(void)
{
	if(USART1_ISR & USART_ISR_TXE) {
		rs485_transfer();
	}

	if(USART1_ISR & USART_ISR_TC) {
		USART1_ICR |= USART_ICR_TCCF;

		if(!usartActive) {
			gpio_clear(RS485_PORT, RS485_DE_PIN);
		}
	}
}


void rs485_enqueue(const char *str)
{
	while(*str) {
		if(bufferFull) {
			break;
		}

		debugBuffer[writePos] = *str;

		writePos++;
		if(writePos == RS485_BUFFER_SIZE) {
			writePos = 0;
		}

		if(writePos == readPos) {
			bufferFull = 1;
		}

		bufferEmpty = 0;

		str++;
	}

	if(!usartActive) {
		usartActive = 1;
		gpio_set(RS485_PORT, RS485_DE_PIN);
		rs485_transfer();
	}
}


void rs485_deepsleep_prepare(void)
{
	// force the transceiver to RX mode
	gpio_clear(RS485_PORT, RS485_DE_PIN);
}


void rs485_deepsleep_resume(void)
{
	// if a transmission is still in progress, switch to TX mode again
	if(usartActive) {
		gpio_set(RS485_PORT, RS485_DE_PIN);
	}
}