TARGET_STM: fix flash api 64bit address alignment on L4 and WB

[ABOSTM]

Summary of changes

fix flash api 64bit address alignment on L4 and WB

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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 test available with misaligned address.

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[ciarmcom]

@ABOSTM, thank you for your changes.
@ARMmbed/mbed-os-maintainers please review.

[kjbracey]

Change isn't wrong, but it would be nice to tidy a bit - get rid of the pointer aliasing and volatile. I'd rather this was

if ((uintptr_t) data % 8 != 0) {
    while ((address < (StartAddress + size)) && (status == 0)) {
        uint64_t data64 = 0;
        for (int i = 0; i < 8; i++) {
            data64 |= (uint64_t) data[i] << (i * 8);
        }
     }

Although I would have thought it should be possible in principle to just case the uint8_t * to a __packed uint64_t * to get the compiler to figure out how to do a potentially-unaligned load. Catch is I don't think either CMSIS or Mbed has the necessary compiler macros to do that portably.

CMSIS has __UNALIGNED_UINT32_READ, but not __UNALIGNED_UINT64_READ. :(

I guess you could just do

while ((address < (StartAddress + size)) && (status == 0)) {
    uint32_t data_low = __UNALIGNED_UINT32_READ(data);
    uint32_t data_high = __UNALIGNED_UINT32_READ(data + 4);
    uint64_t data64 = ((uint64_t) data_high << 32) | data_low;
    if (HAL_FLASH_Program(FLASH_TYPEPROGRAM_DOUBLEWORD, address, data64) == HAL_OK) {

which should be just the same or only a bit off having a direct 64-bit macro.

(And do that unconditionally - don't check for alignment - there's really no need to increase the code size to "speed-optimise" the aligned case).

[jeromecoutant]

Hi

So let's wait for ARM-software/CMSIS_5#768 merge in mbed ?

Then, to be honest, as this looks as optimization, this will not come in our todo list very soon...
So any help and pull requests are welcomed!

Jerome

[kjbracey]

Yeah, okay, we can revisit this when that appears, rather than go for a half-nice version.

[kjbracey]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 11 of 11 test jobs passed
Build number : 1
Build artifacts