Mimxrt1050 lpuart

[grumpyengineer]

Summary of changes

MIMXRT1050_EVK and MIMXRT1170_EVK

Fix bug where calling set_format in MBED (which calls serial_format) causes the CTRL register to become corrupt due to saving its initial value to a uint8_t when the register is 32 bit wide

Change temp variable from uint8_t to uint32_t in serial_api.c

Fixes #15342

Impact of changes

Migration actions required

Documentation

None, bug fix to serial API

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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

Manually tested on MIMXRT1050_EVK, baud rate no longer changes to a random value after calling serialPort->set_format()

Not tested on a MIMXRT1170_EVK as I do not have access to one. Confirmed CTRL register is 32bit in section 71.5.1.8 of the MIMXRT1170 Reference Manual. The lpuart block appears identical across the 1050, 1060 and 1170 model range.

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Reviewers

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[mbed-ci]

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