[lm-sensors] Accelerometer, Gyros and ADC's etc within the kernel.
david-b at pacbell.net
Wed May 28 01:42:42 CEST 2008
On Tuesday 27 May 2008, mark gross wrote:
> > > Another problem area is around SPI itself. There are variations of
> > > device implementations around chip select polarity, clock biasing
> > > (rising,falling, or midpoint) sampling from one SPI part to the next.
> > Midpoint? That's not one I've come across before. All four
> > standard SPI clock/sample/shift modes are already supported
> > in the SPI framework though. Ditto active-high chipselects
> > (vs normal active-low) etc.
> Yeah, its one of the sampling modes for the PIC18F4455 its one of the
> master mode sampling options (see page 194 of
> http://ww1.microchip.com/downloads/en/DeviceDoc/39632D.pdf )
Actually figure 19-3 (p. 198) may be a bit more clear.
Curious. That PIC18F controller has *three* bits ... equivalents
of CPOL and CPHA, plus a bit saying whether to wait a whole or
half clock after the leading clock edge before sampling it.
A quick survey of some other SPI chips suggests that the most
conventional interpretation is to sample on the trailing edge
of the clock, and not presume long hold times.
I would surely hope the SPI interface spec doesn't have to get
into the mess of timing variations which typify anyone trying to
make memory controllers do the Right thing ... *shudder* ...
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