On 2013-07-29 20:19, Peter Stuge wrote:
> Joel Holdsworth wrote:
>>>> The patch considers CS# and decodes MOSI / MISO only after a CS#
>>>> H-L transition.
>>>
>>> What if CS# is tied low?
>>
>> Yes that's a good point. I can think of some chips that require the
>> transition for each packet, or even each byte.
>
> Sure, I know of those too.
>
>
>> Some chips don't care and you can tie CS# low.
>
> Right.
>
>
>> I wonder how important it is to deal with all this.
>
> It makes the difference between sigrok being useful and sigrok
> not being useful. I think it's important that sigrok is useful.
>
>
>> Maybe the CS# behavior could be optional, defaulted to ignore.
>
> Ignore is also not so great. I would suggest a default of only
> sampling when CS# is low, with an option to additionally require
> a H->L transition on CS#, but *always* restarting on a new word
> whenever a H->L transition is seen, regardless of the option value.
>
>
> //Peter
I have tried to draw an example with a wordsize of 4 bits, sampling of
MOSI @ rising edge of SCK & a default SCK value of H.
CS# makes a H-L transition -> decoder starts working; CS# goes H after
frame.
__ ___
CS# |_________________________|
__ __ __ __ _____
SCK |___| |__| |__| |__|
_ ______________
MOSI |___________|
decoder output -> 0011
A CS# H-L transition always starts a new frame (the old frame is left
"unfinished")
__ ________ ________
CS# |___________| |_____________________|
__ __ __ __ __ __ __ ________
SCK |___| |__| |__| |__| |__| |__| |__|
_ _________________
MOSI |___________| |___________________
decoder output -> 00, 1100
The decoder decodes subsequent frames as long as CS# is low
__ ___
CS# |____________________________________________________|
__ __ __ __ __ __ __ __ __________
SCK |___| |__| |__| |__| |__| |__| |__| |__|
_ __________________
MOSI |___________| |_________________________
decoder output -> 0011, 1000
There is a flag which allows the decoder to ignore additional frames
without another CS# H-L transition.
decoder output MOSI -> 0011
Is that what you have in mind?
Regards - Clemens
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