On 22 December 2010 15:11, John Thornton <[email protected]> wrote:

> I'm reading up on bit banging now.

I am almost surprised that there isn't already an SPI bit-banging comp
for EMC2. As long as the components are flexible in their timing then
shifting one bit per base thread ought to be pretty easy.

I did some back-of-the-envelope sums to see if you could run a
blocking function in the servo-thread to twiddle the bits at 500kHz,
but it is just that bit too slow to consider really.  You would need a
system with a 1000nS bas thread to bit-bang at 500kHz, but you would
need to be able to accept a 16uS function runtime in the servo thread
to run it standalone. (it would also need to bypass the parport
driver, and I don't know what the inherent limits of parports are as
regards frequency)

There is already an SPI (And buffered SPI) module in Hostmot2, but no
driver support as yet.

-- 
atp
"Torque wrenches are for the obedience of fools and the guidance of wise men"

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