[sclug] thermometer accessory for my raspberry pi

[Chris Couzens]

Thanks everyone for the help and advice. I'm not going to have time to work
on my ? for a bit. When I do, I'll give a follow up.

Chris

On Thu, Aug 9, 2012 at 3:39 PM, Mark Robson <markxr at gmail.com> wrote:

> Chris, Hi,
>
> A 1k-ohm pull-up resistor is shown on the circuit diagram on page 2. This
> may not be entirely clear.
>
> The protocol is pretty similar to how you described it last night.
>
> Good luck getting the R? to speak that protocol though. Without a
> controller chip of any kind, it's going to be difficult to effectively
> measure the length of pulses which are 25-70 microseconds long.
>
> I suppose a tight loop spinning in kernel-mode busy-reading the GPIO (and
> the clock) could decipher it though, maybe with IRQs disabled. It would
> only need to spin until the end of the packet, which is only 5 bytes ( * 8
> bytes * 75 microseconds) = 4.8 milliseconds.
>
> Trying to read the GPIO at that speed from user-space is going to be
> more-or-less impossible; if any hardware interrupt occurs from another
> device, you'll lose too much time.
>
> Mark
>
>