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 <abbo...@mev.co.uk>
---
drivers/staging/comedi/drivers/comedi_test.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/drivers/staging/comedi/drivers/comedi_test.c
b/drivers/staging/comedi/drivers/comedi_test.c
index 1b3ad7f..9655dc3 100644
--- a/drivers/staging/comedi/drivers/comedi_test.c
+++ b/drivers/staging/comedi/drivers/comedi_test.c
@@ -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);
--
2.6.1
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