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drivers/saul/auto_init: Support bool and percent for dimmers

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Booleans make sense for dimmers when accessed from a Sith application
that deals in absolutes.

Percent values are also a widespread interpretation of brightness
levels, and are thus supported as well.

The bit arithmetic makes sure that the arithmetic operation value / 100
* saul_pwm_resolution is done efficiently (by expression as a
multiplication followed by shifting) and accurately (by maximizing the
number of usable bits) while still being flexible both with respect to
integer sizes and to changes of saul_pwm_resolution.

Co-authored-by: Marian Buschsieweke <marian.buschsieweke@ovgu.de>
This commit is contained in:
chrysn 2020-09-30 23:55:29 +02:00
parent 84414e701f
commit 4687504936
1 changed files with 52 additions and 2 deletions
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54
drivers/saul/pwm_saul.c
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@ -22,6 +22,42 @@
#include "phydat.h"
#include "periph/pwm.h"
#include "saul/periph.h"
#include "bitarithm.h"
/**
* Find factor and shiftback such that for each value entry in the phydat, the
* resulting PWM duty cycle would be (value * factor) >> shiftback.
*/
static int extract_scaling(const phydat_t *state, int *factor, int *shiftback)
{
if (state->scale != 0) {
return -ECANCELED;
}
/** Number of bits i by which we can shift the calculation (value * (255 << i)/100) >> i
* to get a better result than value * 2 (which would otherwise happen in integers) */
int shift100 = bitarithm_msb(INT_MAX) - bitarithm_msb(saul_pwm_resolution);
switch (state->unit) {
case UNIT_UNDEF:
case UNIT_NONE:
*factor = 1;
*shiftback = 0;
break;
case UNIT_BOOL:
*factor = saul_pwm_resolution;
*shiftback = 0;
break;
case UNIT_PERCENT:
*factor = ((int)saul_pwm_resolution << shift100) / 100;
*shiftback = shift100;
break;
default:
return -ECANCELED;
}
return 0;
}
static inline void setchan(const saul_pwm_channel_t *chan, uint16_t value)
{
@ -34,7 +70,14 @@ static int write_dimmer(const void *dev, phydat_t *state)
{
const saul_pwm_dimmer_params_t *p = dev;
setchan(&p->channel, state->val[0]);
int factor, shiftback;
int err = extract_scaling(state, &factor, &shiftback);
if (err < 0) {
return err;
}
setchan(&p->channel, (state->val[0] * factor) >> shiftback);
return 3;
}
@ -48,8 +91,15 @@ static int write_rgb(const void *dev, phydat_t *state)
{
const saul_pwm_rgb_params_t *p = dev;
int factor, shiftback;
int err = extract_scaling(state, &factor, &shiftback);
if (err < 0) {
return err;
}
for (int i = 0; i < 3; ++i) {
setchan(&p->channels[i], state->val[i]);
setchan(&p->channels[i], (state->val[i] * factor) >> shiftback);
}
return 3;
}