I2C does not follow the embedded_hal::i2c::I2c::transaction contract

[dimpolo]

Hi everyone. Could you have a look at bundling same operations in your I2C implementation?
This is required for the pn532 crate to work correctly, see WMT-GmbH/pn532#27

Two consecutive reads should be bundled together.
Two consecutive writes should be bundled together.

Quote from the docs (emphasis mine):

Transaction contract:

• Before executing the first operation an ST is sent automatically. This is followed by SAD+R/W as appropriate.
• Data from adjacent operations of the same type are sent after each other without an SP or SR.
• Between adjacent operations of a different type an SR and SAD+R/W is sent.
• After executing the last operation an SP is sent automatically.
• If the last operation is a Read the master does not send an acknowledge for the last byte.
• ST = start condition
• SAD+R/W = slave address followed by bit 1 to indicate reading or 0 to indicate writing
• SR = repeated start condition
• SP = stop condition

[dimpolo]

Related: rust-embedded/linux-embedded-hal#82
Possible fix: https://github.com/rust-embedded/rust-i2cdev/pull/85/files

[golemparts]

Thank you for opening this issue. If anyone is willing to implement and test this I'm happy to merge in a PR, as I won't be able to work on this myself anytime soon due to other priorities.