Proposed new I2C verb "i2c_repeated_transmit"

[krogozinski]

I2C verb "i2c_repeated_transmit" conducts a write/read sequence a specified number of times.

Use case: many inertial sensors e.g .ST LSM6DS33, employ a FIFO that can be read at a pre-determined time interval or when a certain number of samples have been taken. In order to read and flush this buffer expediently, a fast sequence of I2C operations is required:

• I2C write 1x byte with FIFO data register address (generally lower byte of two-byte word)
• I2C read 2x bytes with FIFO low and FIFO high values
• Repeat for number of words available in FIFO

A repeated transmit I2C verb could rapidly perform this sequence in comparison to a conventional I2CDevice.transmit(), which introduces USB latency between each write/read operation.

Example:

class LSM6DS33(I2CDevice, GreatFETSensor):
    ...
    def get_fifo_words(self, num_words):
        return (self.repeated_transmit(
            [self.REG_FIFO_DATA_OUT_L], # Bytes to write
            2,                          # Number of bytes to read
            num_words))                 # Number of write/read sequence transmissions
    ...

[krogozinski]

@antoinevg is there any appetite to add this new verb? If not, happy to close PR and maintain out-of-tree. Just FYI, I was also looking at implementing same functionality for SPI.

[antoinevg]

This looks great @krogozinski, thank you for contributing! I also think having the same functionality for SPI would be just as useful.

I'm definitely up for putting some time aside to help you get this landed!

[krogozinski]

OK thanks, I should have some time this week to work on the SPI side. I'll make sure to clean up my git commit history before pushing the changes to my fork.