Implemented RS485 driver (TX only)

src/main.c

@@ -15,6 +15,7 @@
 #include <fxp_basic.h>
 
 #include "led_chplex.h"
+#include "rs485.h"
 #include "charge_pump.h"
 #include "power_switch.h"
 
@@ -45,6 +46,9 @@ static void init_clock(void)
 
 	// Port B is needed for the LEDs
 	rcc_periph_clock_enable(RCC_GPIOB);
+
+	// USART1 is used for RS485
+	rcc_periph_clock_enable(RCC_USART1);
 }
 
 
@@ -108,6 +112,7 @@ int main(void)
 	init_clock();
 	init_gpio();
 
+	rs485_init();
 	charge_pump_init();
 	power_switch_init();
 
@@ -116,6 +121,8 @@ int main(void)
 
 	init_systick(1000);
 
+	rs485_enqueue("LNSC-2420 v" VERSION " initialized.\n");
+
 	// triggered every 1 ms
 	while (1) {
 

src/pinout.h

@@ -35,4 +35,12 @@
 #define ANALOG_INPUT_I_SOLAR        3
 #define ANALOG_INPUT_I_LOAD         4
 
+/* RS485 */
+
+#define RS485_PORT        GPIOB
+
+#define RS485_DE_PIN      GPIO5       // High = Driver enabled
+#define RS485_TX_PIN      GPIO6
+#define RS485_RX_PIN      GPIO7
+
 #endif // PINOUT_H

src/rs485.c

@@ -0,0 +1,122 @@
+#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();
+	}
+}

src/rs485.h

@@ -0,0 +1,9 @@
+#ifndef RS485_H
+#define RS485_H
+
+void rs485_init(void);
+void rs485_periodic(void);
+
+void rs485_enqueue(const char *str);
+
+#endif // RS485_H