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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: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ian Abbott 2015-10-27 16:59:20 +00:00 committed by Greg Kroah-Hartman
parent f3f24dff89
commit 4e5ffbf29c
1 changed files with 9 additions and 4 deletions
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13
drivers/staging/comedi/drivers/comedi_test.c
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@ -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);