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OP-1680 Increase the range and resolution of OPLink PPM values

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Encode 511 steps plus a single "invalid" value, rather than 256 steps
plus a dedicated valid flag bit. This gives a range of 990 - 2010 us in
steps of 2 us.
This commit is contained in:
Erik Gustavsson 2015-01-25 13:14:15 +01:00 committed by Karl Knutsson
parent 0d317d1435
commit 966ef5ce75
1 changed files with 31 additions and 9 deletions
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40
flight/pios/common/pios_rfm22b.c
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@ -47,8 +47,8 @@
// 6-byte (32-bit) preamble .. alternating 0's & 1's
// 4-byte (32-bit) sync
// 1-byte packet length (number of data bytes to follow)
// 1 byte valid bitmask
// 8 PPM values (0-255)
// 1 byte PPM values LSB (bit 0)
// 8 bytes PPM values MSBs (bit 8:1)
// 1 byte CRC
//
// *****************************************************************
@ -76,6 +76,14 @@
#define RFM22B_DEFAULT_CHANNEL_SET 24
#define RFM22B_PPM_ONLY_DATARATE RFM22_datarate_9600
// PPM encoding limits
#define RFM22B_PPM_MIN 1
#define RFM22B_PPM_MAX 511
#define RFM22B_PPM_INVALID 0
#define RFM22B_PPM_SCALE 2
#define RFM22B_PPM_MIN_US 990
#define RFM22B_PPM_MAX_US (RFM22B_PPM_MIN_US + (RFM22B_PPM_MAX - RFM22B_PPM_MIN) * RFM22B_PPM_SCALE)
// The maximum amount of time without activity before initiating a reset.
#define PIOS_RFM22B_SUPERVISOR_TIMEOUT 150 // ms
@ -1767,18 +1775,31 @@ static enum pios_radio_event radio_txStart(struct pios_rfm22b_dev *radio_dev)
return RADIO_EVENT_RX_MODE;
}
// The first byte is a bitmask of valid channels.
// The first byte stores the LSB of each channel
p[0] = 0;
// Read the PPM input.
for (uint8_t i = 0; i < RFM22B_PPM_NUM_CHANNELS; ++i) {
int32_t val = radio_dev->ppm[i];
// Clamp and translate value, or transmit as reserved "invalid" constant
if ((val == PIOS_RCVR_INVALID) || (val == PIOS_RCVR_TIMEOUT)) {
p[i + 1] = 0;
val = RFM22B_PPM_INVALID;
} else if (val > RFM22B_PPM_MAX_US) {
val = RFM22B_PPM_MAX;
} else if (val < RFM22B_PPM_MIN_US) {
val = RFM22B_PPM_MIN;
} else {
p[0] |= 1 << i;
p[i + 1] = (val < 1000) ? 0 : ((val >= 1900) ? 255 : (uint8_t)(256 * (val - 1000) / 900));
val = (val - RFM22B_PPM_MIN_US) / RFM22B_PPM_SCALE + RFM22B_PPM_MIN;
}
// Store LSB
if (val & 1) {
p[0] |= (1 << i);
}
// Store upper 8 bits in array
p[i + 1] = val >> 1;
}
// The last byte is a CRC.
@ -1921,10 +1942,11 @@ static enum pios_radio_event radio_receivePacket(struct pios_rfm22b_dev *radio_d
if (good_packet || corrected_packet) {
for (uint8_t i = 0; i < RFM22B_PPM_NUM_CHANNELS; ++i) {
// Calculate 9-bit value taking the LSB from byte 0
uint32_t val = (p[i + 1] << 1) + ((p[0] >> i) & 1);
// Is this a valid channel?
if (p[0] & (1 << i)) {
uint32_t val = p[i + 1];
radio_dev->ppm[i] = (uint16_t)(1000 + val * 900 / 256);
if (val != RFM22B_PPM_INVALID) {
radio_dev->ppm[i] = (uint16_t)(RFM22B_PPM_MIN_US + (val - RFM22B_PPM_MIN) * RFM22B_PPM_SCALE);
} else {
radio_dev->ppm[i] = PIOS_RCVR_INVALID;
}