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Commit 4e5ffbf2 authored by Ian Abbott's avatar Ian Abbott Committed by Greg Kroah-Hartman
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staging: comedi: comedi_test: make timer rate similar to scan rate 



The asynchronous command handling for the analog input subdevice uses a
kernel timer which expires approximately `HZ` times a second.  However,
it only needs to do anything after each scan period.  Set the timer to
expire just after the next scan period.

Although the timer expiry function `waveform_ai_interrupt()` uses
precise time values to generate the fake waveforms used to generate the
data, those time values are constructed in a precise sequence, and do
not depend on the time the timer expiry function is actually called.  So
the timer expiry rate does not have to be very precise.

Signed-off-by: default avatarIan Abbott <abbotti@mev.co.uk>
Reviewed-by: default avatarH Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent f3f24dff

drivers/staging/comedi/drivers/comedi_test.c

+9 −4
Original line number Diff line number Diff line
@@ -52,6 +52,7 @@ 


#include <linux/timer.h>

#include <linux/ktime.h>

#include <linux/jiffies.h>



#define N_CHANS 8
@@ -215,10 +216,12 @@ static void waveform_ai_interrupt(unsigned long arg) 
	if (devpriv->wf_current >= devpriv->wf_period)

		devpriv->wf_current %= devpriv->wf_period;



	if (cmd->stop_src == TRIG_COUNT && async->scans_done >= cmd->stop_arg)

	if (cmd->stop_src == TRIG_COUNT && async->scans_done >= cmd->stop_arg) {

		async->events |= COMEDI_CB_EOA;

	else

		mod_timer(&devpriv->ai_timer, jiffies + 1);

	} else {

		mod_timer(&devpriv->ai_timer,

			  jiffies + usecs_to_jiffies(devpriv->ai_scan_period));

	}



	comedi_handle_events(dev, s);

}
@@ -354,7 +357,9 @@ static int waveform_ai_cmd(struct comedi_device *dev, 
	wf_current = devpriv->ai_last_scan_time;

	devpriv->wf_current = do_div(wf_current, devpriv->wf_period);



	devpriv->ai_timer.expires = jiffies + 1;

	devpriv->ai_timer.expires =

		jiffies + usecs_to_jiffies(devpriv->ai_scan_period);



	/* mark command as active */

	smp_mb__before_atomic();

	set_bit(WAVEFORM_AI_RUNNING, &devpriv->state_bits);