Handle I2C multiplexer channel selection

src/bus/twi.c

@@ -1,12 +1,104 @@
+#include "common.h"
 #include "bus/twi.h"
+
 #include <avr/io.h>
+#include <assert.h>
+
+#define  TW_START        0x08
+#define  TW_REP_START    0x10
+#define  TW_MT_SLA_ACK   0x18
+#define  TW_MT_SLA_NACK  0x20
+#define  TW_MT_DATA_ACK  0x28
+#define  TW_MR_SLA_ACK   0x40
+#define  TW_MR_SLA_NACK  0x48
+#define  TW_MR_DATA_ACK  0x50
 
 int TWI_Init(void)
 {
 	// Set SCL bit rate to 400kHz
 
-	TWSR = 0x00; // TWI status register
-	TWBR = 0x0C; // TWI bit rate register
+	TWSR = 0x00;  // TWI status register
+	TWBR = 0x0C;  // TWI bit rate register
+
+	return 0;
+}
+
+int TWI_Start(char addr, char mode)
+{
+	unsigned int status;
+
+	assert(mode == 0 || mode == 1);
+
+	// Send start condition
+
+	TWCR = (1 << TWEN)    // Enable TWI
+	     | (1 << TWINT)   // Clear interrupt flag
+	     | (1 << TWSTA);  // Send start condition
+
+	// Wait until start condition sent
+
+	while ((TWCR & (1 << TWINT)) == 0);
+	if ((TWSR & 0xf8) != TW_START)
+		return -1;
+
+	// Send slave address
+
+	addr = addr << 1;     // Lowest bit for mode
+	TWDR = addr + mode;   // Mode 0=R, 1=W
+	TWCR = (1 << TWEN)    // Enable TWI
+	     | (1 << TWINT);  // Clear interrupt flag
+
+	// Wait until slave address sent
+
+	while ((TWCR & (1 << TWINT)) == 0);
+	status = TWSR & 0xF8;
+
+	if ((mode == 0 && status != TW_MT_SLA_ACK) ||
+	    (mode == 1 && status != TW_MR_SLA_ACK))
+		return -2;
+
+	return 0;
+}
+
+int TWI_Write(char data)
+{
+	TWDR = data;
+	TWCR = (1 << TWEN)    // Enable TWI
+	     | (1 << TWINT);  // Clear interrupt flag
+
+	while ((TWCR & (1 << TWINT)) == 0);
+
+	if ((TWSR & 0xF8) != TW_MT_DATA_ACK)
+		return -1;
+
+	return 0;
+}
+
+int TWI_Wait_ACK(void)
+{
+	unsigned int status;
+
+	while ((TWCR & (1 << TWINT)) == 0);
+	status = TWSR & 0xF8;
+
+	if (status != TW_MT_DATA_ACK &&
+	    status != TW_MR_DATA_ACK)
+		return -1;
+
+	return 0;
+}
+
+int TWI_Stop(void)
+{
+	// Send stop condition
+
+	TWCR = (1 << TWEN)    // Enable TWI
+	     | (1 << TWINT)   // Clear interrupt flag
+	     | (1 << TWSTO);  // Send stop condition
+
+	// Wait until stop condition sent
+
+	while (TWCR & (1 << TWSTO));
 
 	return 0;
 }

src/bus/twi.h

@@ -2,5 +2,9 @@
 #define MAD_CORE_BUS_TWI_H
 
 int TWI_Init(void);
+int TWI_Start(char addr, char mode);
+int TWI_Write(char data);
+int TWI_Wait_ACK(void);
+int TWI_Stop(void);
 
 #endif // MAD_CORE_BUS_TWI_H

src/bus/usart.c

@@ -1,5 +1,6 @@
 #include "common.h"
 #include "bus/usart.h"
+
 #include <avr/io.h>
 #include <avr/interrupt.h>
 //#include <util/atomic.h>