I2C communication between TCPC and TCPM in the Chromium EC project

[Shruthi]

Hi,

I am working on USB power delivery project which needs to use the APIs available in the chromium EC project to set up an I2C communication between the TCPM and TCPC devices. I am using the STM32F072 board as TCPM (master) and STM32F051 board as TCPC (slave). I was able to find I2C APIs for the master in "/trunk/src/platform/ec/common/i2c.c" file, which has functions like "i2c_read8()", "i2c_write8()", etc. But I couldn't find similar APIs for the slave device. There is a function called "tcpc_i2c_process()" in "/trunk/src/platform/ec/common/usb_pd_tcpc.c", but it didn't seem to work when I used it.

Can anyone please tell me what APIs to use for an I2C communication in the chromium EC project? I also want to know the sequence of function calls to make to set up an I2C connection between the two boards.

Thank you,

Shruthi

[David Hendricks]

Hi Shruthi,

Were you able to find what you needed?

The TCPC-specific functions are defined in files in ec/driver/tcpm. The API is basically the tcpm_drv struct which is defined for each of the TCPMs.

For general I2C communications it seems you found i2c_read8(), i2c_write8(), etc. For TCPMs we generally use the wrappers defined in driver/tcpm/tcpm.h.

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David Hendricks (dhendrix)
Systems Software Engineer, Google Inc.

[Shruthi]

Hi David,

Thanks for replying. I want to implement a policy for power delivery. The document for pdeval-stm32f072 says, "Please duplicate driver/tcpm/tcpci.c into driver/tcpm/##chip#name##.c. Then update the control logic through I2C there.". Does this mean I should implement the power delivery policy in this file (driver/tcpm/##chip#name##.c), by using the I2C APIs you suggested?

Or should I use these APIs from "board/glados_pd/" to communicate with TCPM?

Thank you for your time and awaiting your reply.

Regards,

Shruthi

On Thursday, September 1, 2016 at 8:16:08 PM UTC+2, David Hendricks wrote:

Hi Shruthi,

Were you able to find what you needed?

The TCPC-specific functions are defined in files in ec/driver/tcpm. The API is basically the tcpm_drv struct which is defined for each of the TCPMs.

For general I2C communications it seems you found i2c_read8(), i2c_write8(), etc. For TCPMs we generally use the wrappers defined in driver/tcpm/tcpm.h.

On Mon, Aug 29, 2016 at 6:00 AM, Shruthi <shruthi...@gmail.com> wrote:

Hi,

I am working on USB power delivery project which needs to use the APIs available in the chromium EC project to set up an I2C communication between the TCPM and TCPC devices. I am using the STM32F072 board as TCPM (master) and STM32F051 board as TCPC (slave). I was able to find I2C APIs for the master in "/trunk/src/platform/ec/common/i2c.c" file, which has functions like "i2c_read8()", "i2c_write8()", etc. But I couldn't find similar APIs for the slave device. There is a function called "tcpc_i2c_process()" in "/trunk/src/platform/ec/common/usb_pd_tcpc.c", but it didn't seem to work when I used it.

Can anyone please tell me what APIs to use for an I2C communication in the chromium EC project? I also want to know the sequence of function calls to make to set up an I2C connection between the two boards.

Thank you,

Shruthi

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