Re: gpio(4) and pulsing pins in software

[Reinoud Zandijk <reinoud%NetBSD.org@localhost>]

Hi Mark, hi folks,

On Sun, Sep 25, 2011 at 11:42:11AM +0200, Marc Balmer wrote:
> attached to an individual pin.  gpioctl(8) will keep the pulse keyword,
> as this is needed for hardware pulsating devices.  The interface to the
> gpiopwm(4) driver could be realized using three sysctl variables:
> 
> hw.gpiopwm0.running=0 # Set to 1 to start pwm
> hw.gpiopwm0.ticks_on=n1 # Number of ticks the pin is 1
> hw.gpiopwm0.ticks_off=n2 # Number of ticks the pin is 0
> 
> The current implementation is kind of a hack, since I need a callout_t
> and two integers per pin, if they pulse or not.  Memory is certainly not
> the problem, but I think it's gross nonetheless.

I'd like to be able to set the PWM indepentently for each pin! say specifying
70/256 on and otherwise off.

gpiopwm(4) can be grouped on pins that needs synchronisation. Say gpiopwm0 @
gpio0 has pins 3, 5, 7 with each their pwm's but synchronised on 'on' or 'off'
and gpiopwm1 @ gpio0 has pin 2 and 8. As they are synchronised all the pins
attached can be programmed at one go preventing arbitrary races.

I think it would make the system a lot more powerfull without having clutches
around. Each gpiopwm(4) instance can then have one timer callback and do all
the pin transitions; could be optimised to be even called X pulses later when
the next transition is due.

With regards,
Reinoud