Summary of changes

During testing with my test shield on LPC1768, I noticed an odd issue with SPI: if I set the bus to 16-bit mode and did a transactional transfer, each byte was sent in its own 16-bit word instead of the 16-bit words going out the wire as intended. For example, if I did transfer of [0x1234, 0x5678] with SPI, the logic analyzer would see [0x0034, 0x0012, 0x0078, 0x0056].

As it turns out, this is because of a for loop in the LPC1768 spi_api that has been messed up since its inception. Regardless of what transfer width the bus was set to, it was always looping through each byte of the data and writing that byte individually to the SPI registers.

To fix this, I rewrote the for loop to use a different implementation for transfer width >8 bits. This ensures that the 16-bit words get copied correctly.

I also fixed #255 for this target by implementing spi_get_peripheral_name().

Impact of changes

• Transactional SPI for 16-bit words on LPC1768 fixed
• Every Mbed target should be required to implement spi_get_peripheral_name() #255 fixed for LPC1768

Migration actions required

Documentation

None

Pull request type

[] 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)

Test results

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

CI shield SPI-basic test now passes for LPC1768

Reviewers