/* This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */
/** library for UART communication (code)
 *  @file
 *  @author King Kévin <kingkevin@cuvoodoo.info>
 *  @date 2016-2020
 *  @note peripherals used: USART @ref uart
 */

/* standard libraries */
#include <stdint.h> // standard integer types
#include <stdio.h> // standard I/O facilities
#include <stdlib.h> // general utilities

/* STM32 (including CM3) libraries */
#include <libopencm3/stm32/rcc.h> // real-time control clock library
#include <libopencm3/stm32/gpio.h> // general purpose input output library
#include <libopencm3/stm32/usart.h> // universal synchronous asynchronous receiver transmitter library
#include <libopencm3/cm3/nvic.h> // interrupt handler
#include <libopencmsis/core_cm3.h> // Cortex M3 utilities

#include "spp_rx.h" // own definitions
#include "global.h" // common methods

/** @defgroup spp_uart USART peripheral used for UART communication
 *  @{
 */
#define SPP_UART_ID 3 /**< USART peripheral */
/** @} */

#define UART_BAUDRATE 115200 /**< serial baud rate, in bits per second (with 8N1 8 bits, no parity bit, 1 stop bit settings) */

volatile bool spp_rx_input_available = false;

/* input ring buffer, indexes, and available memory */
static volatile uint8_t spp_rx_input_buffer[64] = {0}; /**< ring buffer for received data */
static volatile uint8_t spp_rx_input_i = 0; /**< current position of read received data */
static volatile uint8_t spp_rx_input_used = 0; /**< how much data has been received and not red */

void spp_rx_setup(void)
{
	/* enable UART I/O peripheral */
	rcc_periph_clock_enable(RCC_USART_PORT(SPP_UART_ID)); // enable clock for UART port peripheral
	rcc_periph_clock_enable(RCC_USART(SPP_UART_ID)); // enable clock for UART peripheral
	rcc_periph_clock_enable(RCC_AFIO); // enable pin alternate function (UART)
	gpio_set_mode(USART_RX_PORT(SPP_UART_ID), GPIO_MODE_INPUT, GPIO_CNF_INPUT_PULL_UPDOWN, USART_RX_PIN(SPP_UART_ID)); // setup GPIO pin UART receive
	gpio_set(USART_RX_PORT(SPP_UART_ID), USART_RX_PIN(SPP_UART_ID)); // pull up to avoid noise when not connected

	/* setup UART parameters */
	usart_set_baudrate(USART(SPP_UART_ID), UART_BAUDRATE);
	usart_set_databits(USART(SPP_UART_ID), 8);
	usart_set_stopbits(USART(SPP_UART_ID), USART_STOPBITS_1);
	usart_set_mode(USART(SPP_UART_ID), USART_MODE_RX);
	usart_set_parity(USART(SPP_UART_ID), USART_PARITY_NONE);
	usart_set_flow_control(USART(SPP_UART_ID), USART_FLOWCONTROL_NONE);

	nvic_enable_irq(USART_IRQ(SPP_UART_ID)); // enable the UART interrupt
	usart_enable_rx_interrupt(USART(SPP_UART_ID)); // enable receive interrupt
	usart_enable(USART(SPP_UART_ID)); // enable UART

	/* reset buffer states */
	spp_rx_input_i = 0;
	spp_rx_input_used = 0;
}

char spp_rx_input_get(void)
{
	if (0 == spp_rx_input_used) { // no data is available
		return 0;
	}
	volatile char to_return = spp_rx_input_buffer[spp_rx_input_i]; // get the next available character
	// there is no need to disable receive interrupt since it won't corrupt the index
	spp_rx_input_i = (spp_rx_input_i + 1) % LENGTH(spp_rx_input_buffer); // update used buffer
	spp_rx_input_used--; // update used buffer
	spp_rx_input_available = (spp_rx_input_used != 0); // update available data
	return to_return;
}

/** UART interrupt service routine called when data has been transmitted or received */
void USART_ISR(SPP_UART_ID)(void)
{
	while (usart_get_flag(USART(SPP_UART_ID), USART_SR_RXNE)) { // data has been received (repeat while receiving)
		char c = usart_recv(USART(SPP_UART_ID)); // save character and free UART buffer (also clears flag)
		if (spp_rx_input_used < LENGTH(spp_rx_input_buffer)) { // only save data if there is space in the buffer
			spp_rx_input_buffer[(spp_rx_input_i + spp_rx_input_used) % LENGTH(spp_rx_input_buffer)] = c; // put character in buffer
			spp_rx_input_used++; // update used buffer
			spp_rx_input_available = true; // update available data
		}
	}
}