Permalink
Browse files

Adding ability to send repeated starts in Wire library.

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
  • Loading branch information...
1 parent 561cd70 commit 2f29f898de9c8375b37269c26948be59a515e801 @damellis damellis committed Feb 19, 2012
Showing with 111 additions and 16 deletions.
  1. +38 −5 libraries/Wire/Wire.cpp
  2. +5 −0 libraries/Wire/Wire.h
  3. +66 −9 libraries/Wire/utility/twi.c
  4. +2 −2 libraries/Wire/utility/twi.h
View
@@ -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" {
@@ -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)
@@ -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;
@@ -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)
View
@@ -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
@@ -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);
@@ -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>
@@ -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;
@@ -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);
@@ -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;
@@ -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;
@@ -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){
@@ -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;
@@ -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;
@@ -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)){
@@ -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
@@ -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;
@@ -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) );

0 comments on commit 2f29f89

Please sign in to comment.