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Subject[PATCH 06/16] staging: comedi: comedi_test: move modulo operations for waveform
Date
The fake waveform generator functions, `fake_sawtooth()` and
`fake_squarewave()`, called from `fake_waveform()`, have a
`current_time` parameter which is the time since the start of a waveform
period. The parameter value may be greater than the waveform period so
they do a modulo operation to bring it into range. Do the modulo
operations outside the functions in `waveform_ai_interrupt()` so that
the waveform generator functions always get a `current_time` parameter
less than the waveform period and do not have to do the modulo operation
themselves. Also, only do the modulo operations when the time since the
start of a waveform exceeds the waveform period. Usually, several
samples are produced in each waveform period and modulo operations are
typically more expensive than a simple comparison.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
---
drivers/staging/comedi/drivers/comedi_test.c | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/drivers/staging/comedi/drivers/comedi_test.c b/drivers/staging/comedi/drivers/comedi_test.c
index cc35bd6..0215228 100644
--- a/drivers/staging/comedi/drivers/comedi_test.c
+++ b/drivers/staging/comedi/drivers/comedi_test.c
@@ -97,7 +97,6 @@ static unsigned short fake_sawtooth(struct comedi_device *dev,
binary_amplitude *= devpriv->uvolt_amplitude;
do_div(binary_amplitude, krange->max - krange->min);

- current_time %= devpriv->usec_period;
value = current_time;
value *= binary_amplitude * 2;
do_div(value, devpriv->usec_period);
@@ -125,7 +124,6 @@ static unsigned short fake_squarewave(struct comedi_device *dev,
const struct comedi_krange *krange =
&s->range_table->range[range_index];

- current_time %= devpriv->usec_period;
value = s->maxdata;
value *= devpriv->uvolt_amplitude;
do_div(value, krange->max - krange->min);
@@ -206,20 +204,24 @@ static void waveform_ai_interrupt(unsigned long arg)

num_scans = comedi_nscans_left(s, num_scans);
for (i = 0; i < num_scans; i++) {
+ unsigned long scan_remain_period = devpriv->scan_period;
+
for (j = 0; j < cmd->chanlist_len; j++) {
unsigned short sample;

+ if (devpriv->usec_current >= devpriv->usec_period)
+ devpriv->usec_current %= devpriv->usec_period;
sample = fake_waveform(dev, CR_CHAN(cmd->chanlist[j]),
CR_RANGE(cmd->chanlist[j]),
- devpriv->usec_current +
- i * devpriv->scan_period +
- j * devpriv->convert_period);
+ devpriv->usec_current);
comedi_buf_write_samples(s, &sample, 1);
+ devpriv->usec_current += devpriv->convert_period;
+ scan_remain_period -= devpriv->convert_period;
}
+ devpriv->usec_current += scan_remain_period;
}
-
- devpriv->usec_current += elapsed_time;
- devpriv->usec_current %= devpriv->usec_period;
+ if (devpriv->usec_current >= devpriv->usec_period)
+ devpriv->usec_current %= devpriv->usec_period;

if (cmd->stop_src == TRIG_COUNT && async->scans_done >= cmd->stop_arg)
async->events |= COMEDI_CB_EOA;
--
2.6.1


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