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[i2c] Clean up target mode transaction boundaries and NACK handling #22460

Merged
merged 4 commits into from
Apr 12, 2024
Merged

[i2c] Clean up target mode transaction boundaries and NACK handling #22460

merged 4 commits into from
Apr 12, 2024

Commits on Apr 12, 2024

  1. [i2c] Eliminate multi-item repeated start entry in ACQ FIFO 

    Change recording of Start symbols to always accompany the address data,
instead of recording a separate R.Start, then Start+address. This helps
maintain certain availability invariants needed for reliable stretching
and NACK handling.

Note that a controller that chooses to do a Repeated Start and address a
*different* target is an unusual case, and it leads to a situation where
the transfer closing symbol won't appear until the Stop or a later
Repeated Start that *does* address this target. While this transaction
style is not explicitly forbidden in the I2C specification, it is not
typically supported in the wild. In any case, software should be able to
resolve this case, and a closing symbol will eventually appear.

Fix up the DV transaction generation to match the expected behavior.

Signed-off-by: Alexander Williams <[email protected]>
    @a-will
    a-will committed Apr 12, 2024
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  2. [i2c] Overhaul target mode NACKing 

    Remove the extra NACK-specific states, generate ACQ FIFO entries at the
point of the NACK timeout, and go to WaitForStop to release SDA and SCL.
Return 0xFF on reads for NACK'd transactions.

Add NackStop as an ACQ FIFO value to indicate the end of transactions
that had errors (generally, NACK'd transfers).

Fix up the glitch sequence to better handle the various states.

Signed-off-by: Alexander Williams <[email protected]>
    @a-will
    a-will committed Apr 12, 2024
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  3. [i2c] Add StretchAcqSetup state to preserve ACK setup time 

    Add StretchAcqSetup state to follow the release of the hold from
StretchAcqFull after the ACQ FIFO gains the necessary space. Continue to
stretch SCL so the change to SDA doesn't violate setup time, then
proceed to the normal ACK setup state.

Remove the immediate write to the ACQ FIFO in the StretchAcqFull state
when we're proceeding to a normal ACK. This created extra ACQ FIFO
writes when it transitioned to the AcquireAckWait state, and the FSM
gets simpler and less error-prone if only error cases operate on FIFOs
outside of the non-stretch states.

Signed-off-by: Alexander Williams <[email protected]>
    @a-will
    a-will committed Apr 12, 2024
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  4. [testutils,i2c] Stop waiting upon receiving a NACK 

    End the transaction wait if the controller receives a NACK.

Signed-off-by: Alexander Williams <[email protected]>
    @a-will
    a-will committed Apr 12, 2024
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