Backwards compatible eh1 SPI support#163
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When we change the transmit / receive masks within a continuous transaction, we might demonstrate an LPSPI hardware defect. In the example shown here, the LPSPI SCK stalls when transmitting the final bit of the final byte, preventing the read from executing. Right now, I'm not sure if this is the LPSPI continuous transaction hardware defect, or if there's an issue in this new driver. I'll shoot for a deeper review later.
mciantyre
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Jun 10, 2024
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The backwards compatibility LGTM. Thanks for sharing this idea!
This looks like a good starting point for an EH1 SPI bus and device implementation. I agree that we can break / extend it later.
I pushed my first test case to this branch. All existing transactions in the loopback test are still working on my 1176 MCU. However, the SpiDevice transaction sequence
spi.transaction(&mut [
TransferInPlace(&mut xfer),
Read(&mut read),
]).unwrap();isn't finishing the TransferInPlace operation. My logic analyzer output is below. It looks like SCK is stuck high, and it's not clocking out the final bit of the final byte.
SCK stuck high before end of transfer
Nothing about the continuous transactions looked obviously questionable, so I'm still digging into the issue.
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This adds impls of eh1's
SpiBusandSpiDevicetraits toLpspiin a backwards compatible manner.At least I think it is backwards compatible. There are some added and changes trait bounds, but they ought to be equivalent to or slightly more permissive than the preexisting ones.
The
DelayNsoperation is not supported and documented as such, since without breaking changes we have no delay provider available to us. Users that needs it can useembedded-hal-busin conjunction with theSpiBusimpl.This is probably not where we want to go long term. The
Lpspitype needs to change to support multiple chip selects, which will probably create a more natural split between the Bus and the Device trait. However, I think it is beneficial to provide a basic impl to users in the meantime.Caveat: I've not yet extensively tested this.