Summary

This implements support for reading/writing slices of memory through themachine.mem{8,16,32} objects. Reading is implemented by returning a memoryview.

After seeing the code size report, I concluded the slice support was not worth adding unconditionally. It is thus gated by theMICROPY_PY_MACHINE_MEMX_SLICE feature flag.

After testing on the ESP32-S3, I encountered an issues where certain registers require word-aligned reads. Thus, trying to usestruct.unpack directly would fail becausemp_binary_get_int reads one byte at a time, but copying the slice usingbytes(machine.mem8[...]) first worked becausememcpy tries to copy entire words at once. To fix this I implemented an extra path inmp_binary_get_int that tries reading entire words when the alignment and endianness work out. This is the cause for most of the code size increase (as it isn't gated behind a feature flag).

Testing

Tested on a few different ESP32 boards.

For example, instead of using thetime.ticks_ms() method we can read out the time directly from the LAC timer / systimer peripheral register usingstruct.unpack():

importmachine,struct,time# ESP32:print('ticks_ms:',time.ticks_ms(),', mem8:',struct.unpack('@Q',machine.mem8[0x3FF5F078:0x3FF5F080])[0]//2000)# ESP32-S3:print('ticks_ms:',time.ticks_ms(),', mem8:',sum(v<<sfors,vinzip((32,0),struct.unpack('@II',machine.mem8[0x60023040:0x60023048])))//16000)

ticks_ms: 12769608 , mem8: 12769608

Trade-offs and Alternatives

First tried implementing the buffer protocol for themachine.mem{8,16,32} objects; however did not include that here due to limitations in memoryview (length and offset fields have limited size, thus only allowing access to low memory addresses).

I also implemented a helper functionmachine.ptr(some_object), which returns the pointer to a MicroPython object. SeeDvdGiessen@d6262c3.

>>>data=0xC0FFEECAFE>>>data,hex(data)(828927560446,'0xc0ffeecafe')>>>machine.mem8[machine.ptr(data)+16:machine.ptr(data)+16+2]=b'\xDE\xC0'>>>data,hex(data)(828927557854,'0xc0ffeec0de')

Fun for a bit of poking around in the MicroPython internals interactively, but that does not seem useful enough for actual users, so I've left it out of this PR.