I2C contract violation about rp-hal

[jannic]

@WBosonic, thanks for the report. I agree this looks wrong. However, are you sure it's an SP (stop) you see between the write operations? I'd expect a SR (repeated start), triggered by https://github.com/rp-rs/rp-hal/blob/main/rp2040-hal/src/i2c/controller.rs#L294:

                if first_byte {
                    if !first_transaction {
                        w.restart().enable();
                    }
                    first_byte = false;
                }

@ithinuel, if I read the git history correctly, that was added in #764. Do you remember why?

[WBosonic]

Ah yes it is an SR (I encountered this bug a while ago and misremembered).

From what I see the user facing I2C transaction does not actually check if the transaction type is the same as the one before.

[jannic]

Ah yes it is an SR (I encountered this bug a while ago and misremembered).

From what I see the user facing I2C transaction does not actually check if the transaction type is the same as the one before.

If I understand the datasheet correctly, it doesn't need to:

1 - If IC_RESTART_EN is 1, a RESTART is issued before the
data is sent/received (according to the value of CMD),
regardless of whether or not the transfer direction is
changing from the previous command; if IC_RESTART_EN
is 0, a STOP followed by a START is issued instead.
0 - If IC_RESTART_EN is 1, a RESTART is issued only if the
transfer direction is changing from the previous
command; if IC_RESTART_EN is 0, a STOP followed by a
START is issued instead.

So the fix could be as easy as removing w.restart().enable(); entirely?

[ithinuel]

Yes, provided that ic_restart_en is set (which it is).