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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
This commit is contained in:
David A. Mellis
2012-02-18 20:05:11 -05:00
parent 561cd7054d
commit 2f29f898de
4 changed files with 111 additions and 16 deletions
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43
libraries/Wire/Wire.cpp
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@ -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" {
@ -73,14 +75,14 @@ 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;
@ -88,9 +90,19 @@ uint8_t TwoWire::requestFrom(uint8_t address, uint8_t quantity)
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)