Strip down the TWI code

- Only implement a single syncronous read/write function to read a byte,
  since that's all we need currently
- Implement a compact IR_SENSOR probe for PAT9125
- Saves 242 bytes compared to PAT9125_SWI2C

Firmware/pat9125.c

@@ -118,9 +118,10 @@ uint8_t pat9125_probe()
     twi_init();
   #ifdef IR_SENSOR
     // NOTE: this is called from the MK3S variant, so it should be kept minimal
-    #error not implemented
+    uint8_t addr = PAT9125_PID1;
+    return (twi_rw8(PAT9125_I2C_ADDR,TW_READ,&addr) == 0);
   #else
-	return pat9125_rd_reg(PAT9125_PID1) != 0;
+    return (pat9125_rd_reg(PAT9125_PID1) != 0);
   #endif
 #endif
 }
@@ -262,8 +263,8 @@ uint8_t pat9125_rd_reg(uint8_t addr)
 	if (!swi2c_readByte_A8(PAT9125_I2C_ADDR, addr, &data)) //NO ACK error
         goto error;
 #elif defined(PAT9125_I2C)
-	if (twi_writeTo(PAT9125_I2C_ADDR,&addr,1,1,0) != 0 ||
-        twi_readFrom(PAT9125_I2C_ADDR,&data,1,1) != 1)
+	if (twi_rw8(PAT9125_I2C_ADDR,TW_WRITE,&addr) ||
+        twi_rw8(PAT9125_I2C_ADDR,TW_READ,&data))
         goto error;
 #endif
 	return data;
@@ -285,8 +286,8 @@ void pat9125_wr_reg(uint8_t addr, uint8_t data)
 	if (!swi2c_writeByte_A8(PAT9125_I2C_ADDR, addr, &data)) //NO ACK error
         goto error;
 #elif defined(PAT9125_I2C)
-	if (twi_writeTo(PAT9125_I2C_ADDR,&addr,1,1,0) != 0 ||
-        twi_writeTo(PAT9125_I2C_ADDR,&data,1,1,1) != 0)
+	if (twi_rw8(PAT9125_I2C_ADDR,TW_WRITE,&addr) ||
+        twi_rw8(PAT9125_I2C_ADDR,TW_READ,&data))
         goto error;
 #endif
     return;

Firmware/twi.c

@@ -1,5 +1,5 @@
 /*
-  twi.c - TWI/I2C library for Wiring & Arduino
+  twi.c - Stripped-down TWI/I2C library
   Copyright (c) 2006 Nicholas Zambetti.  All right reserved.
 
   This library is free software; you can redistribute it and/or
@@ -20,11 +20,6 @@
 */
 
 #include <math.h>
-#include <stdlib.h>
-#include <inttypes.h>
-#include <avr/io.h>
-#include <avr/interrupt.h>
-#include <compat/twi.h>
 #include "Arduino.h" // for digitalWrite
 
 #ifndef cbi
@@ -35,43 +30,11 @@
 #define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
 #endif
 
-#include "pins_arduino.h"
 #include "twi.h"
 
-static volatile uint8_t twi_state;
-static volatile uint8_t twi_slarw;
-static volatile uint8_t twi_sendStop;			// should the transaction end with a stop
-static volatile uint8_t twi_inRepStart;			// in the middle of a repeated start
 
-static void (*twi_onSlaveTransmit)(void);
-static void (*twi_onSlaveReceive)(uint8_t*, int);
-
-static uint8_t twi_masterBuffer[TWI_BUFFER_LENGTH];
-static volatile uint8_t twi_masterBufferIndex;
-static volatile uint8_t twi_masterBufferLength;
-
-static uint8_t twi_txBuffer[TWI_BUFFER_LENGTH];
-static volatile uint8_t twi_txBufferIndex;
-static volatile uint8_t twi_txBufferLength;
-
-static uint8_t twi_rxBuffer[TWI_BUFFER_LENGTH];
-static volatile uint8_t twi_rxBufferIndex;
-
-static volatile uint8_t twi_error;
-
-/* 
- * Function twi_init
- * Desc     readys twi pins and sets twi bitrate
- * Input    none
- * Output   none
- */
 void twi_init(void)
 {
-  // initialize state
-  twi_state = TWI_READY;
-  twi_sendStop = true;		// default value
-  twi_inRepStart = false;
-  
   // activate internal pullups for twi.
   digitalWrite(SDA, 1);
   digitalWrite(SCL, 1);
@@ -85,477 +48,46 @@ void twi_init(void)
   SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR))
   note: TWBR should be 10 or higher for master mode
   It is 72 for a 16mhz Wiring board with 100kHz TWI */
-
-  // enable twi module, acks, and twi interrupt
-  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA);
 }
 
-/* 
- * Function twi_disable
- * Desc     disables twi pins
- * Input    none
- * Output   none
- */
 void twi_disable(void)
 {
-  // disable twi module, acks, and twi interrupt
-  TWCR &= ~(_BV(TWEN) | _BV(TWIE) | _BV(TWEA));
-
   // deactivate internal pullups for twi.
   digitalWrite(SDA, 0);
   digitalWrite(SCL, 0);
 }
 
-/* 
- * Function twi_slaveInit
- * Desc     sets slave address and enables interrupt
- * Input    none
- * Output   none
- */
-void twi_setAddress(uint8_t address)
+uint8_t twi_waitfor(uint8_t status)
 {
-  // set twi slave address (skip over TWGCE bit)
-  TWAR = address << 1;
-}
-
-/* 
- * Function twi_setClock
- * Desc     sets twi bit rate
- * Input    Clock Frequency
- * Output   none
- */
-void twi_setFrequency(uint32_t frequency)
-{
-  TWBR = ((F_CPU / frequency) - 16) / 2;
-  
-  /* twi bit rate formula from atmega128 manual pg 204
-  SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR))
-  note: TWBR should be 10 or higher for master mode
-  It is 72 for a 16mhz Wiring board with 100kHz TWI */
-}
-
-/* 
- * Function twi_readFrom
- * Desc     attempts to become twi bus master and read a
- *          series of bytes from a device on the bus
- * Input    address: 7bit i2c device address
- *          data: pointer to byte array
- *          length: number of bytes to read into array
- *          sendStop: Boolean indicating whether to send a stop at the end
- * Output   number of bytes read
- */
-uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length, uint8_t sendStop)
-{
-  uint8_t i;
-
-  // ensure data will fit into buffer
-  if(TWI_BUFFER_LENGTH < length){
-    return 0;
-  }
-
-  // wait until twi is ready, become master receiver
-  while(TWI_READY != twi_state){
-    continue;
-  }
-  twi_state = TWI_MRX;
-  twi_sendStop = sendStop;
-  // reset error state (0xFF.. no error occured)
-  twi_error = 0xFF;
-
-  // initialize buffer iteration vars
-  twi_masterBufferIndex = 0;
-  twi_masterBufferLength = length-1;  // This is not intuitive, read on...
-  // On receive, the previously configured ACK/NACK setting is transmitted in
-  // response to the received byte before the interrupt is signalled. 
-  // Therefor we must actually set NACK when the _next_ to last byte is
-  // received, causing that NACK to be sent in response to receiving the last
-  // expected byte of data.
-
-  // build sla+w, slave device address + w bit
-  twi_slarw = TW_READ;
-  twi_slarw |= address << 1;
-
-  if (true == twi_inRepStart) {
-    // if we're in the repeated start state, then we've already sent the start,
-    // (@@@ we hope), and the TWI statemachine is just waiting for the address byte.
-    // We need to remove ourselves from the repeated start state before we enable interrupts,
-    // since the ISR is ASYNC, and we could get confused if we hit the ISR before cleaning
-    // up. Also, don't enable the START interrupt. There may be one pending from the 
-    // repeated start that we sent ourselves, and that would really confuse things.
-    twi_inRepStart = false;			// remember, we're dealing with an ASYNC ISR
-    do {
-      TWDR = twi_slarw;
-    } while(TWCR & _BV(TWWC));
-    TWCR = _BV(TWINT) | _BV(TWEA) | _BV(TWEN) | _BV(TWIE);	// enable INTs, but not START
-  }
-  else
-    // send start condition
-    TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTA);
-
-  // wait for read operation to complete
-  while(TWI_MRX == twi_state){
-    continue;
-  }
-
-  if (twi_masterBufferIndex < length)
-    length = twi_masterBufferIndex;
-
-  // copy twi buffer to data
-  for(i = 0; i < length; ++i){
-    data[i] = twi_masterBuffer[i];
-  }
-	
-  return length;
-}
-
-/* 
- * Function twi_writeTo
- * Desc     attempts to become twi bus master and write a
- *          series of bytes to a device on the bus
- * Input    address: 7bit i2c device address
- *          data: pointer to byte array
- *          length: number of bytes in array
- *          wait: boolean indicating to wait for write or not
- *          sendStop: boolean indicating whether or not to send a stop at the end
- * Output   0 .. success
- *          1 .. length to long for buffer
- *          2 .. address send, NACK received
- *          3 .. data send, NACK received
- *          4 .. other twi error (lost bus arbitration, bus error, ..)
- */
-uint8_t twi_writeTo(uint8_t address, uint8_t* data, uint8_t length, uint8_t wait, uint8_t sendStop)
-{
-  uint8_t i;
-
-  // ensure data will fit into buffer
-  if(TWI_BUFFER_LENGTH < length){
-    return 1;
-  }
-
-  // wait until twi is ready, become master transmitter
-  while(TWI_READY != twi_state){
-    continue;
-  }
-  twi_state = TWI_MTX;
-  twi_sendStop = sendStop;
-  // reset error state (0xFF.. no error occured)
-  twi_error = 0xFF;
-
-  // initialize buffer iteration vars
-  twi_masterBufferIndex = 0;
-  twi_masterBufferLength = length;
-  
-  // copy data to twi buffer
-  for(i = 0; i < length; ++i){
-    twi_masterBuffer[i] = data[i];
-  }
-  
-  // build sla+w, slave device address + w bit
-  twi_slarw = TW_WRITE;
-  twi_slarw |= address << 1;
-  
-  // if we're in a repeated start, then we've already sent the START
-  // in the ISR. Don't do it again.
-  //
-  if (true == twi_inRepStart) {
-    // if we're in the repeated start state, then we've already sent the start,
-    // (@@@ we hope), and the TWI statemachine is just waiting for the address byte.
-    // We need to remove ourselves from the repeated start state before we enable interrupts,
-    // since the ISR is ASYNC, and we could get confused if we hit the ISR before cleaning
-    // up. Also, don't enable the START interrupt. There may be one pending from the 
-    // repeated start that we sent outselves, and that would really confuse things.
-    twi_inRepStart = false;			// remember, we're dealing with an ASYNC ISR
-    do {
-      TWDR = twi_slarw;				
-    } while(TWCR & _BV(TWWC));
-    TWCR = _BV(TWINT) | _BV(TWEA) | _BV(TWEN) | _BV(TWIE);	// enable INTs, but not START
-  }
-  else
-    // send start condition
-    TWCR = _BV(TWINT) | _BV(TWEA) | _BV(TWEN) | _BV(TWIE) | _BV(TWSTA);	// enable INTs
-
-  // wait for write operation to complete
-  while(wait && (TWI_MTX == twi_state)){
-    continue;
-  }
-  
-  if (twi_error == 0xFF)
-    return 0;	// success
-  else if (twi_error == TW_MT_SLA_NACK)
-    return 2;	// error: address send, nack received
-  else if (twi_error == TW_MT_DATA_NACK)
-    return 3;	// error: data send, nack received
-  else
-    return 4;	// other twi error
+    while(!(TWCR & _BV(TWINT)));
+    return (TW_STATUS != status);
 }
 
-/* 
- * Function twi_transmit
- * Desc     fills slave tx buffer with data
- *          must be called in slave tx event callback
- * Input    data: pointer to byte array
- *          length: number of bytes in array
- * Output   1 length too long for buffer
- *          2 not slave transmitter
- *          0 ok
- */
-uint8_t twi_transmit(const uint8_t* data, uint8_t length)
+uint8_t twi_rw8(uint8_t address, uint8_t mode, uint8_t* data)
 {
-  uint8_t i;
+  // send start condition
+  TWCR = _BV(TWEN) | _BV(TWINT) | _BV(TWSTA);
+  if(twi_waitfor(TW_START))
+      return 1;
+
+  // send address
+  TWDR = mode;
+  TWDR |= (address << 1);
+  TWCR = _BV(TWEN) | _BV(TWINT);
+  if(twi_waitfor(mode == TW_READ? TW_MR_SLA_ACK: TW_MT_SLA_ACK))
+      return 2;
+
+  // send or receive data
+  if(mode == TW_WRITE)
+      TWDR = *data;
+  TWCR = _BV(TWEN) | _BV(TWINT);
+  if(twi_waitfor(mode == TW_READ? TW_MR_DATA_NACK: TW_MT_DATA_ACK))
+      return 3;
+  if(mode == TW_READ)
+      *data = TWDR;
+
+  // send stop
+  TWCR = _BV(TWEN) | _BV(TWINT) | _BV(TWSTO);
 
-  // ensure data will fit into buffer
-  if(TWI_BUFFER_LENGTH < (twi_txBufferLength+length)){
-    return 1;
-  }
-  
-  // ensure we are currently a slave transmitter
-  if(TWI_STX != twi_state){
-    return 2;
-  }
-  
-  // set length and copy data into tx buffer
-  for(i = 0; i < length; ++i){
-    twi_txBuffer[twi_txBufferLength+i] = data[i];
-  }
-  twi_txBufferLength += length;
-  
   return 0;
 }
-
-/* 
- * Function twi_attachSlaveRxEvent
- * Desc     sets function called before a slave read operation
- * Input    function: callback function to use
- * Output   none
- */
-void twi_attachSlaveRxEvent( void (*function)(uint8_t*, int) )
-{
-  twi_onSlaveReceive = function;
-}
-
-/* 
- * Function twi_attachSlaveTxEvent
- * Desc     sets function called before a slave write operation
- * Input    function: callback function to use
- * Output   none
- */
-void twi_attachSlaveTxEvent( void (*function)(void) )
-{
-  twi_onSlaveTransmit = function;
-}
-
-/* 
- * Function twi_reply
- * Desc     sends byte or readys receive line
- * Input    ack: byte indicating to ack or to nack
- * Output   none
- */
-void twi_reply(uint8_t ack)
-{
-  // transmit master read ready signal, with or without ack
-  if(ack){
-    TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWINT) | _BV(TWEA);
-  }else{
-	  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWINT);
-  }
-}
-
-/* 
- * Function twi_stop
- * Desc     relinquishes bus master status
- * Input    none
- * Output   none
- */
-void twi_stop(void)
-{
-  // send stop condition
-  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTO);
-
-  // wait for stop condition to be exectued on bus
-  // TWINT is not set after a stop condition!
-  while(TWCR & _BV(TWSTO)){
-    continue;
-  }
-
-  // update twi state
-  twi_state = TWI_READY;
-}
-
-/* 
- * Function twi_releaseBus
- * Desc     releases bus control
- * Input    none
- * Output   none
- */
-void twi_releaseBus(void)
-{
-  // release bus
-  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT);
-
-  // update twi state
-  twi_state = TWI_READY;
-}
-
-ISR(TWI_vect)
-{
-  switch(TW_STATUS){
-    // All Master
-    case TW_START:     // sent start condition
-    case TW_REP_START: // sent repeated start condition
-      // copy device address and r/w bit to output register and ack
-      TWDR = twi_slarw;
-      twi_reply(1);
-      break;
-
-    // Master Transmitter
-    case TW_MT_SLA_ACK:  // slave receiver acked address
-    case TW_MT_DATA_ACK: // slave receiver acked data
-      // if there is data to send, send it, otherwise stop 
-      if(twi_masterBufferIndex < twi_masterBufferLength){
-        // copy data to output register and ack
-        TWDR = twi_masterBuffer[twi_masterBufferIndex++];
-        twi_reply(1);
-      }else{
-	if (twi_sendStop)
-          twi_stop();
-	else {
-	  twi_inRepStart = true;	// we're gonna send the START
-	  // don't enable the interrupt. We'll generate the start, but we 
-	  // avoid handling the interrupt until we're in the next transaction,
-	  // at the point where we would normally issue the start.
-	  TWCR = _BV(TWINT) | _BV(TWSTA)| _BV(TWEN) ;
-	  twi_state = TWI_READY;
-	}
-      }
-      break;
-    case TW_MT_SLA_NACK:  // address sent, nack received
-      twi_error = TW_MT_SLA_NACK;
-      twi_stop();
-      break;
-    case TW_MT_DATA_NACK: // data sent, nack received
-      twi_error = TW_MT_DATA_NACK;
-      twi_stop();
-      break;
-    case TW_MT_ARB_LOST: // lost bus arbitration
-      twi_error = TW_MT_ARB_LOST;
-      twi_releaseBus();
-      break;
-
-    // Master Receiver
-    case TW_MR_DATA_ACK: // data received, ack sent
-      // put byte into buffer
-      twi_masterBuffer[twi_masterBufferIndex++] = TWDR;
-    case TW_MR_SLA_ACK:  // address sent, ack received
-      // ack if more bytes are expected, otherwise nack
-      if(twi_masterBufferIndex < twi_masterBufferLength){
-        twi_reply(1);
-      }else{
-        twi_reply(0);
-      }
-      break;
-    case TW_MR_DATA_NACK: // data received, nack sent
-      // put final byte into buffer
-      twi_masterBuffer[twi_masterBufferIndex++] = TWDR;
-	if (twi_sendStop)
-          twi_stop();
-	else {
-	  twi_inRepStart = true;	// we're gonna send the START
-	  // don't enable the interrupt. We'll generate the start, but we 
-	  // avoid handling the interrupt until we're in the next transaction,
-	  // at the point where we would normally issue the start.
-	  TWCR = _BV(TWINT) | _BV(TWSTA)| _BV(TWEN) ;
-	  twi_state = TWI_READY;
-	}    
-	break;
-    case TW_MR_SLA_NACK: // address sent, nack received
-      twi_stop();
-      break;
-    // TW_MR_ARB_LOST handled by TW_MT_ARB_LOST case
-
-    // Slave Receiver
-    case TW_SR_SLA_ACK:   // addressed, returned ack
-    case TW_SR_GCALL_ACK: // addressed generally, returned ack
-    case TW_SR_ARB_LOST_SLA_ACK:   // lost arbitration, returned ack
-    case TW_SR_ARB_LOST_GCALL_ACK: // lost arbitration, returned ack
-      // enter slave receiver mode
-      twi_state = TWI_SRX;
-      // indicate that rx buffer can be overwritten and ack
-      twi_rxBufferIndex = 0;
-      twi_reply(1);
-      break;
-    case TW_SR_DATA_ACK:       // data received, returned ack
-    case TW_SR_GCALL_DATA_ACK: // data received generally, returned ack
-      // if there is still room in the rx buffer
-      if(twi_rxBufferIndex < TWI_BUFFER_LENGTH){
-        // put byte in buffer and ack
-        twi_rxBuffer[twi_rxBufferIndex++] = TWDR;
-        twi_reply(1);
-      }else{
-        // otherwise nack
-        twi_reply(0);
-      }
-      break;
-    case TW_SR_STOP: // stop or repeated start condition received
-      // ack future responses and leave slave receiver state
-      twi_releaseBus();
-      // put a null char after data if there's room
-      if(twi_rxBufferIndex < TWI_BUFFER_LENGTH){
-        twi_rxBuffer[twi_rxBufferIndex] = '\0';
-      }
-      // callback to user defined callback
-      twi_onSlaveReceive(twi_rxBuffer, twi_rxBufferIndex);
-      // since we submit rx buffer to "wire" library, we can reset it
-      twi_rxBufferIndex = 0;
-      break;
-    case TW_SR_DATA_NACK:       // data received, returned nack
-    case TW_SR_GCALL_DATA_NACK: // data received generally, returned nack
-      // nack back at master
-      twi_reply(0);
-      break;
-    
-    // Slave Transmitter
-    case TW_ST_SLA_ACK:          // addressed, returned ack
-    case TW_ST_ARB_LOST_SLA_ACK: // arbitration lost, returned ack
-      // enter slave transmitter mode
-      twi_state = TWI_STX;
-      // ready the tx buffer index for iteration
-      twi_txBufferIndex = 0;
-      // set tx buffer length to be zero, to verify if user changes it
-      twi_txBufferLength = 0;
-      // request for txBuffer to be filled and length to be set
-      // note: user must call twi_transmit(bytes, length) to do this
-      twi_onSlaveTransmit();
-      // if they didn't change buffer & length, initialize it
-      if(0 == twi_txBufferLength){
-        twi_txBufferLength = 1;
-        twi_txBuffer[0] = 0x00;
-      }
-      // transmit first byte from buffer, fall
-    case TW_ST_DATA_ACK: // byte sent, ack returned
-      // copy data to output register
-      TWDR = twi_txBuffer[twi_txBufferIndex++];
-      // if there is more to send, ack, otherwise nack
-      if(twi_txBufferIndex < twi_txBufferLength){
-        twi_reply(1);
-      }else{
-        twi_reply(0);
-      }
-      break;
-    case TW_ST_DATA_NACK: // received nack, we are done 
-    case TW_ST_LAST_DATA: // received ack, but we are done already!
-      // ack future responses
-      twi_reply(1);
-      // leave slave receiver state
-      twi_state = TWI_READY;
-      break;
-
-    // All
-    case TW_NO_INFO:   // no state information
-      break;
-    case TW_BUS_ERROR: // bus error, illegal stop/start
-      twi_error = TW_BUS_ERROR;
-      twi_stop();
-      break;
-  }
-}
-

Firmware/twi.h

@@ -1,5 +1,5 @@
 /*
-  twi.h - TWI/I2C library for Wiring & Arduino
+  twi.h - Stripped-down TWI/I2C library
   Copyright (c) 2006 Nicholas Zambetti.  All right reserved.
 
   This library is free software; you can redistribute it and/or
@@ -17,39 +17,37 @@
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
 
-#ifndef twi_h
-#define twi_h
-
-  #include <inttypes.h>
-
-  //#define ATMEGA8
-
-  #ifndef TWI_FREQ
-  #define TWI_FREQ 400000L
-  #endif
-
-  #ifndef TWI_BUFFER_LENGTH
-  #define TWI_BUFFER_LENGTH 32
-  #endif
-
-  #define TWI_READY 0
-  #define TWI_MRX   1
-  #define TWI_MTX   2
-  #define TWI_SRX   3
-  #define TWI_STX   4
-  
-  void twi_init(void);
-  void twi_disable(void);
-  void twi_setAddress(uint8_t);
-  void twi_setFrequency(uint32_t);
-  uint8_t twi_readFrom(uint8_t, uint8_t*, uint8_t, uint8_t);
-  uint8_t twi_writeTo(uint8_t, uint8_t*, uint8_t, uint8_t, uint8_t);
-  uint8_t twi_transmit(const uint8_t*, uint8_t);
-  void twi_attachSlaveRxEvent( void (*)(uint8_t*, int) );
-  void twi_attachSlaveTxEvent( void (*)(void) );
-  void twi_reply(uint8_t);
-  void twi_stop(void);
-  void twi_releaseBus(void);
+#pragma once
 
+#include <inttypes.h>
+#include <compat/twi.h>
+
+#ifndef TWI_FREQ
+#define TWI_FREQ 400000L
 #endif
 
+/*
+ * Function twi_init
+ * Desc     readys twi pins and sets twi bitrate
+ * Input    none
+ * Output   none
+ */
+void twi_init(void);
+
+/*
+ * Function twi_disable
+ * Desc     disables twi pins
+ * Input    none
+ * Output   none
+ */
+void twi_disable(void);
+
+/*
+ * Function twi_rw8
+ * Desc     read/write a single byte from a device
+ * Input    address: 7bit i2c device address
+ *          mode: TW_READ or TW_WRITE
+ *          data: pointer to byte
+ * Output   0 on success
+ */
+uint8_t twi_rw8(uint8_t address, uint8_t mode, uint8_t* data);