SOLVED — How to Implement Clock Stretching for I²C on Tiva C?

[Rei Vilo 695]

See post at http://forum.43oh.com/topic/5130-help-—-how-to-implement-clock-stretching-for-i²c-on-tiva-c/?p=45240

 

Edit — Solved with pull request at http://github.com/energia/Energia/pull/375

[Rei Vilo 695]

Here's the solution that I've tested on port I²C (3) of the Stellaris LM4F120 and Tiva C TM4C123 LaunchPads.

 

Libraries to include with #include "Wire.h"

#include "driverlib/i2c.h"

#include "driverlib/sysctl.h"

#include "driverlib/gpio.h"

This routine initialise the SCL pin. Not sure it is really useful.

void stretchInit()

{

  SysCtlPeripheralEnable(I2C_SCL3_PERIPH);

}

This routine configures the SCL line as a standard output and sets it LOW. Not sure about the 4mA parameter.

void stretchPause()

{

  // Standard output

  GPIOPadConfigSet(I2C_SCL3_BASE, I2C_SCL3_PIN, GPIO_STRENGTH_4MA, GPIO_PIN_TYPE_STD);

  GPIODirModeSet(I2C_SCL3_BASE, I2C_SCL3_PIN, GPIO_DIR_MODE_OUT);

  // Set LOW

  GPIOPinWrite(I2C_SCL3_BASE, I2C_SCL3_PIN, 0);

}

This routine configures the SCL line back to normal. I tried another option but it didn't work.

void stretchResume()

{

  // Reconfigure for I2C

  ROM_GPIOPinConfigure(GPIO_PD0_I2C3SCL);

  ROM_GPIOPinTypeI2CSCL(I2C_SCL3_BASE, I2C_SCL3_PIN);


// Doesn't work

// HIGH for floating?

// GPIOPinWrite(I2C_SCL3_BASE, I2C_SCL3_PIN, I2C_SCL3_PIN);

// Open drain

// GPIOPadConfigSet(I2C_SCL3_BASE, I2C_SCL3_PIN, GPIO_STRENGTH_2MA, GPIO_PIN_TYPE_OD);

// GPIODirModeSet(I2C_SCL3_BASE, I2C_SCL3_PIN, GPIO_DIR_MODE_HW);

}

Typical usage requires

• adding stretchInit(); in setup()
  
• including stretchPause(); on the first line of void ReceiveEvent(int howMany) as the I²C sequence is buffered
  
• placing stretchResume(); on the last line of the routine in charge of executing orders from I²C.
  

Questions:

• How to make it universal for the 4 I²C ports available in the LM4F and TM4C MCUs?
  
• How to integrate the routines directly into the Wire.h library?
  
• How to check the whole process is safe —which values for pull-up resistors, which parameter for mA, no shorts, no damage for the MCU?
  

Thanks!

[Rei Vilo 695]

I've integrated the solution into the Wire library and prepared a pull-request.

 

See

• ticket at https://github.com/energia/Energia/issues/336
• pull request at https://github.com/energia/Energia/pull/375

 

I've tested it on LM4F120- and TM4C123-based LaunchPads
 

Please proceed with other tests and commit!