On 8/9/2013 8:08 AM, Andrew wrote:
> Hello,
> 
> I'm trying to set up BeagleBone using Charles' image (with HDMI display).
> As I do not have any cape board I simply connect A4988 drivers to BBB's
> output pins.
> K9.HDMI config has 4 stepgens, but I'd like to have 6 or 7. It loads with
> num_stepgens=6 but the question is which output pins can I use for two or
> three extra stepgens?

Any I/O pins that are not already used by something else.  The PRU code
is capable of driving any pin in the 4 32-bit banks of GPIO, as well as
the 16 directly-connected low-latency PRU output pins.

To calculate a pin number to use for the GPIO banks:

Pin# = ((gpio_bank + 1) * 32) + pin_number

...this is the same as the kernel pin numbering scheme, except one is
added to the GPIO bank so that zero results in an invalid pin number and
means "don't drive any pin".  This is to keep things safe since all pin
numbers default to zero the way HAL shared memory gets initialized, you
have to explicitly set a pin number before the PRU actually tries to
twiddle something.

-- 
Charles Steinkuehler
[email protected]

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