Try to make BMP280 communication more resilient

If communication times out or a NAK is received, this is now recognized
and sensor values are flagged as invalid. The communication then
restarts on the next regular cycle. This is still to be tested.

src/bmp280.c

@@ -16,7 +16,8 @@ typedef enum {
 	WAIT_MEASUREMENT_COMPLETE,
 	READ_RESULTS,
 	COMPENSATE_TEMPERATURE,
-	COMPENSATE_PRESSURE
+	COMPENSATE_PRESSURE,
+	ERROR   // set by the I²C callback in case of errors/timeout
 } bmp280_readout_state_t;
 
 static bmp280_readout_state_t m_readout_state;
@@ -45,7 +46,7 @@ static int32_t m_temp_raw;
 static int32_t m_press_raw;
 
 
-static void cb_i2c_dma(const uint8_t *rdata, size_t rlen);
+static void cb_i2c_dma(i2c_dma_evt_t evt, const uint8_t *rdata, size_t rlen);
 
 
 bool bmp280_init(void)
@@ -151,10 +152,12 @@ static void trigger_read_results(void)
 }
 
 
-static void cb_i2c_dma(const uint8_t *rdata, size_t rlen)
+static void cb_i2c_dma(i2c_dma_evt_t evt, const uint8_t *rdata, size_t rlen)
 {
 	(void)rlen;
 
+	switch(evt) {
+		case I2C_DMA_EVT_TRANSFER_COMPLETE:
 			switch(m_readout_state) {
 				case SEND_REQUEST:
 					m_readout_state = WAIT_MEASUREMENT_COMPLETE;
@@ -191,6 +194,13 @@ static void cb_i2c_dma(const uint8_t *rdata, size_t rlen)
 					while(1);
 					break;
 			}
+			break;
+
+		case I2C_DMA_EVT_TIMEOUT:
+		case I2C_DMA_EVT_NAK:
+			m_readout_state = ERROR;
+			break;
+	}
 }
 
 
@@ -218,7 +228,13 @@ bool bmp280_loop(void)
 			m_last_pressure = bmp280_comp_pressure(m_press_raw);
 			m_readout_state = READY;
 			m_measurements_valid = true;
-			retval = true;
+			retval = true; // measurement complete
+			break;
+
+		case ERROR:
+			m_readout_state = READY;
+			m_measurements_valid = false;
+			retval = true; // measurement cycle terminated
 			break;
 	}
 

src/bmp280.h

@@ -7,7 +7,7 @@
 #include <fxp.h>
 
 bool bmp280_init(void);
-bool bmp280_loop(void); // returns true if measurements have been updated
+bool bmp280_loop(void); // returns true when measurement cycle has terminated (successfully or with error)
 
 bool bmp280_start_measurement(void);
 

src/i2c_dma.c

@@ -8,6 +8,8 @@
 #define DMA_CHANNEL_TX DMA_CHANNEL2
 #define DMA_CHANNEL_RX DMA_CHANNEL3
 
+#define TIMEOUT_COUNTER_VALUE 100 // milliseconds
+
 static uint8_t m_wdata[2];
 static uint8_t m_wlen;
 static uint8_t m_rdata[32];
@@ -16,6 +18,8 @@ static uint8_t m_rlen;
 static uint8_t m_addr;
 static uint32_t m_i2c;
 
+static uint32_t m_timeout_counter;
+
 typedef enum {
 	IDLE,
 	SEND_DATA,
@@ -101,9 +105,16 @@ void i2c_dma_loop(void)
 				} else {
 					// no RX requested => we are done here
 					m_state = IDLE;
-					m_callback(NULL, 0);
+					m_callback(I2C_DMA_EVT_TRANSFER_COMPLETE, NULL, 0);
 				}
 			}
+
+			if(I2C_ISR(m_i2c) & I2C_ISR_NACKF) {
+				// there should be no NACK during the transfer => abort
+				I2C_ICR(m_i2c) |= I2C_ICR_NACKCF; // clear the interrupt flag
+				m_state = IDLE;
+				m_callback(I2C_DMA_EVT_NAK, NULL, 0);
+			}
 			break;
 
 		case RECEIVE_DATA:
@@ -112,10 +123,22 @@ void i2c_dma_loop(void)
 				dma_clear_interrupt_flags(DMA1, DMA_CHANNEL_RX, DMA_TCIF);
 
 				m_state = IDLE;
-				m_callback(m_rdata, m_rlen);
+				m_callback(I2C_DMA_EVT_TRANSFER_COMPLETE, m_rdata, m_rlen);
+			}
+
+			if(I2C_ISR(m_i2c) & I2C_ISR_NACKF) {
+				// there should be no NACK during the transfer => abort
+				I2C_ICR(m_i2c) |= I2C_ICR_NACKCF; // clear the interrupt flag
+				m_state = IDLE;
+				m_callback(I2C_DMA_EVT_NAK, NULL, 0);
 			}
 			break;
 	}
+
+	m_timeout_counter--;
+	if(m_timeout_counter == 0) {
+		m_callback(I2C_DMA_EVT_TIMEOUT, NULL, 0);
+	}
 }
 
 
@@ -141,6 +164,8 @@ void i2c_dma_start_transfer7(uint32_t i2c, uint8_t addr, const uint8_t *w, size_
 		i2c_enable_autoend(i2c); // stop condition after write transfer
 	}
 
+	m_timeout_counter = TIMEOUT_COUNTER_VALUE;
+
 	i2c_send_start(i2c); // start the transfer. The rest is handled by the DMA.
 	setup_txdma();
 }

src/i2c_dma.h

@@ -7,10 +7,11 @@
 typedef enum
 {
 	I2C_DMA_EVT_TRANSFER_COMPLETE,
-	I2C_DMA_EVT_ADDR_NAK,
+	I2C_DMA_EVT_NAK,
+	I2C_DMA_EVT_TIMEOUT,
 } i2c_dma_evt_t;
 
-typedef void (*i2c_dma_callback_t)(const uint8_t *rdata, size_t rlen);
+typedef void (*i2c_dma_callback_t)(i2c_dma_evt_t evt, const uint8_t *rdata, size_t rlen);
 
 void i2c_dma_init(i2c_dma_callback_t callback);