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feat: implement channel helpers

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cel_crsf_channel_us_to_val() and cel_crsf_channel_val_to_us()
convert between microseconds (988-2012) and 11-bit values (172-1811)
with rounding. cel_crsf_channel_default() fills safe/disarmed values.
This commit is contained in:
portersky
2026-06-14 20:54:56 +02:00
parent a846b063f9
commit 8b181d0fcd
2 changed files with 87 additions and 16 deletions
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celrs/crsf.c
+22 -16
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@@ -124,28 +124,34 @@ int16_t cel_crsf_channel_clamp(int16_t value) {
}
int16_t cel_crsf_channel_us_to_val(uint16_t us) {
/* TODO: convert microseconds to 11-bit channel value.
* Linear mapping: 988us -> 172, 2012us -> 1811.
* value = (us - 988) * (1811 - 172) / (2012 - 988) + 172
* Clamp result to [CEL_CRSF_CH_MIN, CEL_CRSF_CH_MAX]. */
(void)us;
return CEL_CRSF_CH_MID;
/* Clamp to valid range first to avoid underflow */
if (us < 988) us = 988;
if (us > 2012) us = 2012;
/* Round to nearest: add half the divisor before dividing */
int16_t value = (int16_t)(
((us - 988) * (CEL_CRSF_CH_MAX - CEL_CRSF_CH_MIN)
+ (2012 - 988) / 2) / (2012 - 988)
+ CEL_CRSF_CH_MIN);
return cel_crsf_channel_clamp(value);
}
uint16_t cel_crsf_channel_val_to_us(int16_t value) {
/* TODO: convert 11-bit channel value to microseconds.
* Linear mapping: 172 -> 988us, 1811 -> 2012us.
* us = (value - 172) * (2012 - 988) / (1811 - 172) + 988 */
(void)value;
return 1500;
value = cel_crsf_channel_clamp(value);
return (uint16_t)(
((value - CEL_CRSF_CH_MIN) * (2012 - 988)
+ (CEL_CRSF_CH_MAX - CEL_CRSF_CH_MIN) / 2)
/ (CEL_CRSF_CH_MAX - CEL_CRSF_CH_MIN) + 988);
}
void cel_crsf_channel_default(int16_t channels[16]) {
/* TODO: fill with safe/disarmed values.
* CH1-Roll, CH2-Pitch, CH4-Yaw = CEL_CRSF_CH_MID (centered)
* CH3-Throttle = CEL_CRSF_CH_MIN (zero)
* CH5..CH16 (AUX) = CEL_CRSF_CH_MIN (off) */
(void)channels;
memset(channels, 0, sizeof(int16_t) * 16);
channels[0] = CEL_CRSF_CH_MID; /* roll */
channels[1] = CEL_CRSF_CH_MID; /* pitch */
channels[2] = CEL_CRSF_CH_MIN; /* throttle */
channels[3] = CEL_CRSF_CH_MID; /* yaw */
for (int i = 4; i < 16; i++) {
channels[i] = CEL_CRSF_CH_MIN;
}
}
/* --------------------------------------------------------------------------- */