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Code Issues Releases Activity

LP-536 skip informational UBX packets that are too large to fit buffers

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UBX-NAV-SVINFO (id 30) and UBX-NAV-SAT (id 35) packets are NOT critical to the navigation.
Their only use is to update the nice GPS constellation widget in the GCS.
These packets become very large when a lot of SV (Space Vehicles) are tracked. (8 + 12 * <number of SV>) bytes

In the case of 3 simultaneously enabled GNSS, it is easy to reach the currently defined tracking limit of 32 SV.
The memory taken up by this is 8 + 12 * 32 = 392 bytes

The NEO-M8N has been seen to send out information for more than 32 SV. This causes overflow errors.
We will ignore these informational packets if they become too large.
The downside of this is no more constellation updates in the GCS when we reach the limit.

An alternative fix could be to increment the maximum number of satellites: MAX_SVS and UBX_CFG_GNSS_NUMCH_VER8 in UBX.h
This would use extra memory for little gain. Both fixes can be combined.

Tests indicate that, once we reach this amount of tracked SV, the NEO-M8N module positioning output
becomes jittery (in time) and therefore less accurate.

The recommendation is to limit the maximum number of simultaneously used GNSS to a value of 2.
This will help keep the number of tracked satellites in line.
This commit is contained in:
Jan NIJS 2017-06-23 16:26:32 +02:00
parent 2d181994f0
commit 5e53fb283c
1 changed files with 28 additions and 1 deletions
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29
flight/modules/GPS/UBX.c
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@ -173,8 +173,35 @@ int parse_ubx_stream(uint8_t *rx, uint16_t len, char *gps_rx_buffer, GPSPosition
#if defined(PIOS_GPS_MINIMAL)
restart_state = RESTART_NO_ERROR;
#else
restart_state = RESTART_WITH_ERROR;
/* UBX-NAV-SVINFO (id 30) and UBX-NAV-SAT (id 35) packets are NOT critical to the navigation.
Their only use is to update the nice GPS constellation widget in the GCS.
These packets become very large when a lot of SV (Space Vehicles) are tracked. (8 + 12 * <number of SV>) bytes
In the case of 3 simultaneously enabled GNSS, it is easy to reach the currently defined tracking limit of 32 SV.
The memory taken up by this is 8 + 12 * 32 = 392 bytes
The NEO-M8N has been seen to send out information for more than 32 SV. This causes overflow errors.
We will ignore these informational packets if they become too large.
The downside of this is no more constellation updates in the GCS when we reach the limit.
An alternative fix could be to increment the maximum number of satellites: MAX_SVS and UBX_CFG_GNSS_NUMCH_VER8 in UBX.h
This would use extra memory for little gain. Both fixes can be combined.
Tests indicate that, once we reach this amount of tracked SV, the NEO-M8N module positioning output
becomes jittery (in time) and therefore less accurate.
The recommendation is to limit the maximum number of simultaneously used GNSS to a value of 2.
This will help keep the number of tracked satellites in line.
*/
if ( (ubx->header.class == 0x01) && ( (ubx->header.id == 0x30) || (ubx->header.id == 0x35) ) ) {
restart_state = RESTART_NO_ERROR;
} else {
restart_state = RESTART_WITH_ERROR;
}
#endif
// We won't see the end of the packet. Which means it is useless to do any further processing.
// Therefore scan for the start of the next packet.
proto_state = START;
break;
} else {
if (ubx->header.len == 0) {