STM32 I2C v2 HAL: Fix repeated starts in transaction mode

[multiplemonomials]

Summary of changes

When testing with a U-Blox GPS, I noticed that there's an issue in the new STM32 I2C HAL added by #78 . Trying to do a repeated start using the transactional API:

    // Set read address to 1
    uint8_t const readAddr = 0x01;
    TEST_ASSERT_EQUAL(I2C::Result::ACK, i2c->write(EEPROM_I2C_ADDRESS, reinterpret_cast<const char *>(&readAddr), 1, true));

    // Read the byte back
    uint8_t readByte = 0;
    TEST_ASSERT_EQUAL(I2C::Result::ACK, i2c->read(EEPROM_I2C_ADDRESS | 1, reinterpret_cast<char *>(&readByte), 1));
    TEST_ASSERT_EQUAL_UINT8(0x3, readByte);

simply does not work:

This is because the code in get_hal_xfer_options() was returning I2C_LAST_FRAME for the case of stop=false, which is patently wrong -- it should be I2C_FIRST_FRAME, to indicate that we want a start condition but not a stop. I think I inherited this code from the original implementation, but I should have trusted my gut that this wasn't right...

However, that wasn't the only issue. Simply changing I2C_LAST_FRAME to I2C_FIRST_FRAME did fix the repeated starts, but created another issue where some of the test cases would time out trying to do I2C operations. It turns out there's some really wacky logic in the STM32 HAL code where, if you pass that constant and it detects that the previous transfer was the same type of transfer, it simply won't set the START flag. Which... causes it to hang forever and not send any data. Really not sure why it does this. Seriously, I'm scratching my head.

Luckily, the fix is pretty simple: use I2C_OTHER_FRAME instead of I2C_FIRST_FRAME, which activates additional logic which disables the other logic which cancels the start condition. So, we really just want to be using OTHER_FRAME everywhere.

With the new code, I can generate repeated start conditions properly:

Impact of changes

Migration actions required

Documentation

None

Pull request type

[X] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[X] Tests / results supplied as part of this PR

I ran the I2C test suite (same as #78) and passed all the tests.

Reviewers

@JohnK1987
@JojoS62

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[multiplemonomials]

@JohnK1987 @JojoS62 could you take a look at this?