Re: Errant readings on LM81 with T2080 SoC

Chris Packham
2021-03-11T21:18:36Z

On 11/03/21 9:18 pm, Wolfram Sang wrote:
>> Bummer. What is really weird is that you see clock stretching under
>> CPU load. Normally clock stretching is triggered by the device, not
>> by the host.
> One example: Some hosts need an interrupt per byte to know if they
> should send ACK or NACK. If that interrupt is delayed, they stretch the
> clock.
>
It feels like something like that is happening. Looking at the T2080
Reference manual there is an interesting timing diagram (Figure 14-2 if
someone feels like looking it up). It shows SCL low between the ACK for
the address and the data byte. I think if we're delayed in sending the
next byte we could violate Ttimeout or Tlow:mext from the SMBUS spec.