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Adding ability to send repeated starts in Wire library.
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This adds an additional (boolean) parameter to both endTransmission() and requestFrom(), which specifies whether or not to send a stop condition after the corresponding transmission.  This defaults to true, as in the previous behavior of the library.

http://code.google.com/p/arduino/issues/detail?id=663
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@damellis
damellis committed Feb 19, 2012
1 parent 561cd70 commit 2f29f89
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Showing 4 changed files with 111 additions and 16 deletions.
43 changes: 38 additions & 5 deletions libraries/Wire/Wire.cpp
View file
Expand Up @@ -15,6 +15,8 @@
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
Modified 2012 by Todd Krein (todd@krein.org) to implement repeated starts
*/

extern "C" {
Expand Down Expand Up @@ -73,24 +75,34 @@ void TwoWire::begin(int address)
begin((uint8_t)address);
}

uint8_t TwoWire::requestFrom(uint8_t address, uint8_t quantity)
uint8_t TwoWire::requestFrom(uint8_t address, uint8_t quantity, uint8_t sendStop)
{
// clamp to buffer length
if(quantity > BUFFER_LENGTH){
quantity = BUFFER_LENGTH;
}
// perform blocking read into buffer
uint8_t read = twi_readFrom(address, rxBuffer, quantity);
uint8_t read = twi_readFrom(address, rxBuffer, quantity, sendStop);
// set rx buffer iterator vars
rxBufferIndex = 0;
rxBufferLength = read;

return read;
}

uint8_t TwoWire::requestFrom(uint8_t address, uint8_t quantity)
{
return requestFrom((uint8_t)address, (uint8_t)quantity, (uint8_t)true);
}

uint8_t TwoWire::requestFrom(int address, int quantity)
{
return requestFrom((uint8_t)address, (uint8_t)quantity);
return requestFrom((uint8_t)address, (uint8_t)quantity, (uint8_t)true);
}

uint8_t TwoWire::requestFrom(int address, int quantity, int sendStop)
{
return requestFrom((uint8_t)address, (uint8_t)quantity, (uint8_t)sendStop);
}

void TwoWire::beginTransmission(uint8_t address)
Expand All @@ -109,10 +121,23 @@ void TwoWire::beginTransmission(int address)
beginTransmission((uint8_t)address);
}

uint8_t TwoWire::endTransmission(void)
//
// Originally, 'endTransmission' was an f(void) function.
// It has been modified to take one parameter indicating
// whether or not a STOP should be performed on the bus.
// Calling endTransmission(false) allows a sketch to
// perform a repeated start.
//
// WARNING: Nothing in the library keeps track of whether
// the bus tenure has been properly ended with a STOP. It
// is very possible to leave the bus in a hung state if
// no call to endTransmission(true) is made. Some I2C
// devices will behave oddly if they do not see a STOP.
//
uint8_t TwoWire::endTransmission(uint8_t sendStop)
{
// transmit buffer (blocking)
int8_t ret = twi_writeTo(txAddress, txBuffer, txBufferLength, 1);
int8_t ret = twi_writeTo(txAddress, txBuffer, txBufferLength, 1, sendStop);
// reset tx buffer iterator vars
txBufferIndex = 0;
txBufferLength = 0;
Expand All @@ -121,6 +146,14 @@ uint8_t TwoWire::endTransmission(void)
return ret;
}

// This provides backwards compatibility with the original
// definition, and expected behaviour, of endTransmission
//
uint8_t TwoWire::endTransmission(void)
{
return endTransmission(true);
}

// must be called in:
// slave tx event callback
// or after beginTransmission(address)
Expand Down
5 changes: 5 additions & 0 deletions libraries/Wire/Wire.h
View file
Expand Up @@ -15,6 +15,8 @@
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
Modified 2012 by Todd Krein (todd@krein.org) to implement repeated starts
*/

#ifndef TwoWire_h
Expand Down Expand Up @@ -50,8 +52,11 @@ class TwoWire : public Stream
void beginTransmission(uint8_t);
void beginTransmission(int);
uint8_t endTransmission(void);
uint8_t endTransmission(uint8_t);
uint8_t requestFrom(uint8_t, uint8_t);
uint8_t requestFrom(uint8_t, uint8_t, uint8_t);
uint8_t requestFrom(int, int);
uint8_t requestFrom(int, int, int);
virtual size_t write(uint8_t);
virtual size_t write(const uint8_t *, size_t);
virtual int available(void);
Expand Down
75 changes: 66 additions & 9 deletions libraries/Wire/utility/twi.c
View file
Expand Up @@ -15,6 +15,8 @@
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
Modified 2012 by Todd Krein (todd@krein.org) to implement repeated starts
*/

#include <math.h>
Expand All @@ -37,14 +39,16 @@
#include "twi.h"

static volatile uint8_t twi_state;
static uint8_t twi_slarw;
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 uint8_t twi_masterBufferLength;
static volatile uint8_t twi_masterBufferLength;

static uint8_t twi_txBuffer[TWI_BUFFER_LENGTH];
static volatile uint8_t twi_txBufferIndex;
Expand All @@ -65,6 +69,8 @@ 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);
Expand Down Expand Up @@ -103,9 +109,10 @@ void twi_setAddress(uint8_t address)
* 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 twi_readFrom(uint8_t address, uint8_t* data, uint8_t length, uint8_t sendStop)
{
uint8_t i;

Expand All @@ -119,6 +126,7 @@ uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length)
continue;
}
twi_state = TWI_MRX;
twi_sendStop = sendStop;
// reset error state (0xFF.. no error occured)
twi_error = 0xFF;

Expand All @@ -135,8 +143,20 @@ uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length)
twi_slarw = TW_READ;
twi_slarw |= address << 1;

// send start condition
TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTA);
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
TWDR = twi_slarw;
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){
Expand All @@ -162,13 +182,14 @@ uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length)
* 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 twi_writeTo(uint8_t address, uint8_t* data, uint8_t length, uint8_t wait, uint8_t sendStop)
{
uint8_t i;

Expand All @@ -182,6 +203,7 @@ uint8_t twi_writeTo(uint8_t address, uint8_t* data, uint8_t length, uint8_t wait
continue;
}
twi_state = TWI_MTX;
twi_sendStop = sendStop;
// reset error state (0xFF.. no error occured)
twi_error = 0xFF;

Expand All @@ -198,8 +220,23 @@ uint8_t twi_writeTo(uint8_t address, uint8_t* data, uint8_t length, uint8_t wait
twi_slarw = TW_WRITE;
twi_slarw |= address << 1;

// send start condition
TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTA);
// 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
TWDR = twi_slarw;
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)){
Expand Down Expand Up @@ -343,7 +380,16 @@ SIGNAL(TWI_vect)
TWDR = twi_masterBuffer[twi_masterBufferIndex++];
twi_reply(1);
}else{
twi_stop();
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
Expand Down Expand Up @@ -374,6 +420,17 @@ SIGNAL(TWI_vect)
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;
Expand Down
4 changes: 2 additions & 2 deletions libraries/Wire/utility/twi.h
View file
Expand Up @@ -40,8 +40,8 @@

void twi_init(void);
void twi_setAddress(uint8_t);
uint8_t twi_readFrom(uint8_t, uint8_t*, uint8_t);
uint8_t twi_writeTo(uint8_t, uint8_t*, uint8_t, uint8_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) );
Expand Down

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