bmp280: read out via DMA in the background

This removes any busy waiting on the I²C from the main loop.
Initialization is still done in a blocking way.

src/bmp280.c

@@ -1,6 +1,8 @@
 #include <libopencm3/stm32/i2c.h>
 #include <libopencm3/stm32/gpio.h>
 
+#include "i2c_dma.h"
+
 #include "pinout.h"
 
 #include "bmp280_comp.h"
@@ -8,6 +10,17 @@
 
 #define BMP280_7BIT_ADDR 0x76
 
+typedef enum {
+	READY,
+	SEND_REQUEST,
+	WAIT_MEASUREMENT_COMPLETE,
+	READ_RESULTS,
+	COMPENSATE_TEMPERATURE,
+	COMPENSATE_PRESSURE
+} bmp280_readout_state_t;
+
+static bmp280_readout_state_t m_readout_state;
+
 // calibration value cache, shared with bmp280_comp.c
 
 extern uint16_t dig_T1;
@@ -27,6 +40,13 @@ extern  int16_t dig_P9;
 static fxp_t m_last_temperature = 0;
 static fxp_t m_last_pressure = 0;
 
+static int32_t m_temp_raw;
+static int32_t m_press_raw;
+
+
+static void cb_i2c_dma(const uint8_t *rdata, size_t rlen);
+
+
 bool bmp280_init(void)
 {
 	// configure pins for I2C1
@@ -95,6 +115,8 @@ bool bmp280_init(void)
 	dig_P8 =  (((int16_t)(int8_t)rdata[21]) << 8) | rdata[20]; // 0x9C, 0x9D
 	dig_P9 =  (((int16_t)(int8_t)rdata[23]) << 8) | rdata[22]; // 0x9E, 0x9F
 
+	i2c_dma_init(cb_i2c_dma);
+
 	return true;
 
 err_out:
@@ -102,63 +124,123 @@ err_out:
 }
 
 
+static void trigger_read_status_register(void)
+{
+	uint8_t wdata[1];
+	uint8_t wsize = 0, rsize;
+
+	wdata[wsize++] = 0xF3; // status register
+	rsize = 1;
+
+	i2c_dma_start_transfer7(I2C1, BMP280_7BIT_ADDR, wdata, wsize, rsize);
+}
+
+
+static void trigger_read_results(void)
+{
+	uint8_t wdata[1];
+	uint8_t wsize = 0, rsize;
+
+	wdata[wsize++] = 0xF7;
+	rsize = 8;
+
+	i2c_dma_start_transfer7(I2C1, BMP280_7BIT_ADDR, wdata, wsize, rsize);
+}
+
+
+static void cb_i2c_dma(const uint8_t *rdata, size_t rlen)
+{
+	(void)rlen;
+
+	switch(m_readout_state) {
+		case SEND_REQUEST:
+			m_readout_state = WAIT_MEASUREMENT_COMPLETE;
+			trigger_read_status_register();
+			break;
+
+		case WAIT_MEASUREMENT_COMPLETE:
+			if((rdata[0] & 0x09) != 0) {
+				// either "measuring" or "im_update" is active, so measurement is not complete yet.
+				// try again:
+				trigger_read_status_register();
+			} else {
+				m_readout_state = READ_RESULTS;
+				trigger_read_results();
+			}
+			break;
+
+		case READ_RESULTS:
+			m_press_raw =
+				((int32_t)rdata[0] << 12)         // press_msb (0xF7)
+				| ((int32_t)rdata[1] << 4)        // press_lsb (0xF8)
+				| ((int32_t)rdata[2] >> 4);       // press_xlsb (0xF9)
+
+			m_temp_raw =
+				((int32_t)rdata[3] << 12)         // temp_msb (0xFA)
+				| ((int32_t)rdata[4] << 4)        // temp_lsb (0xFB)
+				| ((int32_t)rdata[5] >> 4);       // temp_xlsb (0xFC)
+
+			m_readout_state = COMPENSATE_TEMPERATURE;
+			break;
+
+		default:
+			// should never happen
+			while(1);
+			break;
+	}
+}
+
+
+bool bmp280_loop(void)
+{
+	bool retval = false;
+
+	switch(m_readout_state) {
+		case READY:
+			// nothing to do in this state
+			break;
+
+		case SEND_REQUEST:
+		case WAIT_MEASUREMENT_COMPLETE:
+		case READ_RESULTS:
+			// handled in cb_i2c_dma exclusively
+			break;
+
+		case COMPENSATE_TEMPERATURE:
+			m_last_temperature = bmp280_comp_temperature(m_temp_raw);
+			m_readout_state = COMPENSATE_PRESSURE;
+			break;
+
+		case COMPENSATE_PRESSURE:
+			m_last_pressure = bmp280_comp_pressure(m_press_raw);
+			m_readout_state = READY;
+			retval = true;
+			break;
+	}
+
+	if(m_readout_state != READY) {
+		i2c_dma_loop();
+	}
+
+	return retval;
+}
+
+
 bool bmp280_start_measurement(void)
 {
 	uint8_t wdata[2];
 	uint8_t wsize = 0;
 
+	if(m_readout_state != READY) {
+		return false; // still busy
+	}
+
 	wdata[wsize++] = 0xF4; // measurement control register
 	wdata[wsize++] = (0x01 << 5) | (0x01 << 2) | 0x01; // pressure x1, temp x1, forced mode
 
-	i2c_transfer7(I2C1, BMP280_7BIT_ADDR, wdata, wsize, NULL, 0);
+	i2c_dma_start_transfer7(I2C1, BMP280_7BIT_ADDR, wdata, wsize, 0);
 
-	return true;
+	m_readout_state = SEND_REQUEST;
-}
-
-
-bool bmp280_is_measurement_complete(void)
-{
-	uint8_t wdata[1];
-	uint8_t rdata[1];
-	uint8_t wsize = 0, rsize;
-
-	wdata[wsize++] = 0xF3; // status register
-	rsize = 1;
-
-	i2c_transfer7(I2C1, BMP280_7BIT_ADDR, wdata, wsize, rdata, rsize);
-
-	if((rdata[0] & 0x09) != 0) {
-		// either "measuring" or "im_update" is active, so measurement is not complete yet.
-		return false;
-	} else {
-		return true;
-	}
-}
-
-
-bool bmp280_readout_and_compensate(void)
-{
-	uint8_t wdata[1];
-	uint8_t rdata[8];
-	uint8_t wsize = 0, rsize;
-
-	wdata[wsize++] = 0xF7;
-	rsize = 8;
-
-	i2c_transfer7(I2C1, BMP280_7BIT_ADDR, wdata, wsize, rdata, rsize);
-
-	int32_t press_raw =
-		((int32_t)rdata[0] << 12)         // press_msb (0xF7)
-		| ((int32_t)rdata[1] << 4)        // press_lsb (0xF8)
-		| ((int32_t)rdata[2] >> 4);       // press_xlsb (0xF9)
-
-	int32_t temp_raw =
-		((int32_t)rdata[3] << 12)         // temp_msb (0xFA)
-		| ((int32_t)rdata[4] << 4)        // temp_lsb (0xFB)
-		| ((int32_t)rdata[5] >> 4);       // temp_xlsb (0xFC)
-
-	m_last_temperature = bmp280_comp_temperature(temp_raw);
-	m_last_pressure = bmp280_comp_pressure(press_raw);
 
 	return true;
 }

src/bmp280.h

@@ -7,10 +7,9 @@
 #include <fxp.h>
 
 bool bmp280_init(void);
+bool bmp280_loop(void); // returns true if measurements have been updated
 
 bool bmp280_start_measurement(void);
-bool bmp280_is_measurement_complete(void);
-bool bmp280_readout_and_compensate(void);
 
 fxp_t bmp280_get_temperature(void);
 fxp_t bmp280_get_pressure(void);

src/i2c_dma.c

@@ -0,0 +1,148 @@
+#include <string.h>
+
+#include <libopencm3/stm32/i2c.h>
+#include <libopencm3/stm32/dma.h>
+
+#include "i2c_dma.h"
+
+#include "rs485.h"
+
+#define DMA_CHANNEL_TX DMA_CHANNEL2
+#define DMA_CHANNEL_RX DMA_CHANNEL3
+
+static uint8_t m_wdata[2];
+static uint8_t m_wlen;
+static uint8_t m_rdata[32];
+static uint8_t m_rlen;
+
+static uint8_t m_addr;
+static uint32_t m_i2c;
+
+typedef enum {
+	IDLE,
+	SEND_DATA,
+	RECEIVE_DATA
+} i2c_dma_state_t;
+
+static i2c_dma_state_t m_state;
+
+
+static i2c_dma_callback_t m_callback;
+
+static void setup_txdma(void)
+{
+	dma_channel_reset(DMA1, DMA_CHANNEL_TX);
+
+	dma_set_priority(DMA1, DMA_CHANNEL_TX, DMA_CCR_PL_LOW);
+	dma_set_memory_size(DMA1, DMA_CHANNEL_TX, DMA_CCR_MSIZE_8BIT);
+	dma_set_peripheral_size(DMA1, DMA_CHANNEL_TX, DMA_CCR_PSIZE_8BIT);
+	dma_enable_memory_increment_mode(DMA1, DMA_CHANNEL_TX);
+	dma_set_read_from_memory(DMA1, DMA_CHANNEL_TX);
+	dma_set_peripheral_address(DMA1, DMA_CHANNEL_TX, (uint32_t) &I2C_TXDR(m_i2c));
+
+	// send m_wlen bytes from m_wdata
+	dma_set_memory_address(DMA1, DMA_CHANNEL_TX, (uint32_t)m_wdata);
+	dma_set_number_of_data(DMA1, DMA_CHANNEL_TX, m_wlen);
+
+	dma_enable_channel(DMA1, DMA_CHANNEL_TX);
+
+	i2c_enable_txdma(m_i2c);
+}
+
+
+static void setup_rxdma(void)
+{
+	dma_channel_reset(DMA1, DMA_CHANNEL_RX);
+
+	dma_set_priority(DMA1, DMA_CHANNEL_RX, DMA_CCR_PL_LOW);
+	dma_set_memory_size(DMA1, DMA_CHANNEL_RX, DMA_CCR_MSIZE_8BIT);
+	dma_set_peripheral_size(DMA1, DMA_CHANNEL_RX, DMA_CCR_PSIZE_8BIT);
+	dma_enable_memory_increment_mode(DMA1, DMA_CHANNEL_RX);
+	dma_set_read_from_peripheral(DMA1, DMA_CHANNEL_RX);
+	dma_set_peripheral_address(DMA1, DMA_CHANNEL_RX, (uint32_t) &I2C_RXDR(m_i2c));
+
+	// receive m_rlen bytes and store them in m_rdata
+	dma_set_memory_address(DMA1, DMA_CHANNEL_RX, (uint32_t)m_rdata);
+	dma_set_number_of_data(DMA1, DMA_CHANNEL_RX, m_rlen);
+
+	dma_enable_channel(DMA1, DMA_CHANNEL_RX);
+
+	i2c_enable_rxdma(m_i2c);
+}
+
+
+void i2c_dma_init(i2c_dma_callback_t callback)
+{
+	m_callback = callback;
+
+	m_state = IDLE;
+}
+
+
+void i2c_dma_loop(void)
+{
+	switch(m_state) {
+		case IDLE:
+			// nothing to do
+			return;
+
+		case SEND_DATA:
+			//if(i2c_transfer_complete(m_i2c)) { // does not work for some reason :(
+			if(dma_get_interrupt_flag(DMA1, DMA_CHANNEL_TX, DMA_TCIF)) {
+				dma_clear_interrupt_flags(DMA1, DMA_CHANNEL_TX, DMA_TCIF);
+
+				if(m_rlen) {
+					m_state = RECEIVE_DATA;
+
+					i2c_set_7bit_address(m_i2c, m_addr);
+					i2c_set_read_transfer_dir(m_i2c);
+					i2c_set_bytes_to_transfer(m_i2c, m_rlen);
+					i2c_send_start(m_i2c);
+					i2c_enable_autoend(m_i2c); // important to do it after start() for a proper repeated start!
+					setup_rxdma();
+				} else {
+					// no RX requested => we are done here
+					m_state = IDLE;
+					m_callback(NULL, 0);
+				}
+			}
+			break;
+
+		case RECEIVE_DATA:
+			//if(i2c_transfer_complete(m_i2c)) { // does not work for some reason :(
+			if(dma_get_interrupt_flag(DMA1, DMA_CHANNEL_RX, DMA_TCIF)) {
+				dma_clear_interrupt_flags(DMA1, DMA_CHANNEL_RX, DMA_TCIF);
+
+				m_state = IDLE;
+				m_callback(m_rdata, m_rlen);
+			}
+			break;
+	}
+}
+
+
+void i2c_dma_start_transfer7(uint32_t i2c, uint8_t addr, const uint8_t *w, size_t wn, size_t rn)
+{
+	m_wlen = wn;
+	m_rlen = rn;
+
+	memcpy(m_wdata, w, wn);
+
+	m_state = SEND_DATA;
+
+	m_i2c = i2c;
+	m_addr = addr;
+
+	i2c_set_7bit_address(i2c, addr);
+	i2c_set_write_transfer_dir(i2c);
+	i2c_set_bytes_to_transfer(i2c, wn);
+
+	if(rn) {
+		i2c_disable_autoend(i2c); // prepare repeated start
+	} else {
+		i2c_enable_autoend(i2c); // stop condition after write transfer
+	}
+
+	i2c_send_start(i2c); // start the transfer. The rest is handled by the DMA.
+	setup_txdma();
+}

src/i2c_dma.h

@@ -0,0 +1,21 @@
+#ifndef I2C_DMA_H
+#define I2C_DMA_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+typedef enum
+{
+	I2C_DMA_EVT_TRANSFER_COMPLETE,
+	I2C_DMA_EVT_ADDR_NAK,
+} i2c_dma_evt_t;
+
+typedef void (*i2c_dma_callback_t)(const uint8_t *rdata, size_t rlen);
+
+void i2c_dma_init(i2c_dma_callback_t callback);
+
+void i2c_dma_loop(void);
+
+void i2c_dma_start_transfer7(uint32_t i2c, uint8_t addr, const uint8_t *w, size_t wn, size_t rn);
+
+#endif // I2C_DMA_H

src/main.c

@@ -27,7 +27,6 @@ static enum {
 	BMP280_NOT_PRESENT,
 	BMP280_IDLE,
 	BMP280_MEASURING,
-	BMP280_READOUT
 } bmp280_state;
 
 /* Set up systick to fire freq times per second */
@@ -280,14 +279,9 @@ static void handle_bmp280(uint64_t timebase_ms)
 			break;
 
 		case BMP280_MEASURING:
-			if(timebase_ms % 10 == 0 && bmp280_is_measurement_complete()) {
+			if(timebase_ms % 10 == 0 && bmp280_loop()) {
-				bmp280_state = BMP280_READOUT;
-			}
-			break;
-
-		case BMP280_READOUT:
-			bmp280_readout_and_compensate();
 				bmp280_state = BMP280_IDLE;
+			}
 			break;
 	}
 }