Telemetry Bandwidth

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Telemetry Burst describes the allocation of telemetry packets in ExpressLRS added in #472. There are two types of packets, LINK and DATA. LINK is the standard link statistics and is always available, and DATA is "Advanced Telemetry" which is telemetry coming from the flight controller and shares bandwidth with MSP transfers. Burst mode attempts to maintain a minimum rate of LINK packets and use the rest of the available telemetry slots for DATA.

The LINK rate chosen was one every 512ms, roughly 2 per second but slightly higher to allow more rates to have an additional burst packet at lower ratios.

Air Rate	Telem Ratio	Telem Interval (ms)	Packets/second	Burst Count	Bandwidth (no Burst)	Bandwidth (Burst)
500	1:128	256	3.9	1	78bps	78bps
500	1:64	128	7.8	3	156bps	234bps
500	1:32	64	15.6	7	312bps	547bps
500	1:16	32	31.2	15	625bps	1172bps
500	1:8	16	62.5	31	1250bps	2422bps
500	1:4	8	125.0	63	2500bps	4922bps
500	1:2	4	250.0	127	5000bps	9922bps
Air Rate	Telem Ratio	Telem Interval (ms)	Packets/second	Burst Count	Bandwidth (no Burst)	Bandwidth (Burst)
250	1:128	512	2.0	1	39bps	39bps
250	1:64	256	3.9	1	78bps	78bps
250	1:32	128	7.8	3	156bps	234bps
250	1:16	64	15.6	7	312bps	547bps
250	1:8	32	31.2	15	625bps	1172bps
250	1:4	16	62.5	31	1250bps	2422bps
250	1:2	8	125.0	63	2500bps	4922bps
Air Rate	Telem Ratio	Telem Interval (ms)	Packets/second	Burst Count	Bandwidth (no Burst)	Bandwidth (Burst)
200	1:128	640	1.6	1	31bps	31bps
200	1:64	320	3.1	1	62bps	62bps
200	1:32	160	6.2	2	125bps	167bps
200	1:16	80	12.5	5	250bps	417bps
200	1:8	40	25.0	11	500bps	917bps
200	1:4	20	50.0	24	1000bps	1920bps
200	1:2	10	100.0	50	2000bps	3922bps
Air Rate	Telem Ratio	Telem Interval (ms)	Packets/second	Burst Count	Bandwidth (no Burst)	Bandwidth (Burst)
150	1:128	853	1.2	1	23bps	23bps
150	1:64	426	2.3	1	47bps	47bps
150	1:32	213	4.7	1	94bps	94bps
150	1:16	106	9.4	3	188bps	281bps
150	1:8	53	18.8	8	375bps	667bps
150	1:4	26	37.5	18	750bps	1421bps
150	1:2	13	75.0	37	1500bps	2921bps
Air Rate	Telem Ratio	Telem Interval (ms)	Packets/second	Burst Count	Bandwidth (no Burst)	Bandwidth (Burst)
100	1:128	1280	0.8	1	16bps	16bps
100	1:64	640	1.6	1	31bps	31bps
100	1:32	320	3.1	1	62bps	62bps
100	1:16	160	6.2	2	125bps	167bps
100	1:8	80	12.5	5	250bps	417bps
100	1:4	40	25.0	11	500bps	917bps
100	1:2	20	50.0	24	1000bps	1920bps
Air Rate	Telem Ratio	Telem Interval (ms)	Packets/second	Burst Count	Bandwidth (no Burst)	Bandwidth (Burst)
50	1:128	2560	0.4	1	8bps	8bps
50	1:64	1280	0.8	1	16bps	16bps
50	1:32	640	1.6	1	31bps	31bps
50	1:16	320	3.1	1	62bps	62bps
50	1:8	160	6.2	2	125bps	167bps
50	1:4	80	12.5	5	250bps	417bps
50	1:2	40	25.0	11	500bps	917bps
Air Rate	Telem Ratio	Telem Interval (ms)	Packets/second	Burst Count	Bandwidth (no Burst)	Bandwidth (Burst)
25	1:128	5120	0.2	1	4bps	4bps
25	1:64	2560	0.4	1	8bps	8bps
25	1:32	1280	0.8	1	16bps	16bps
25	1:16	640	1.6	1	31bps	31bps
25	1:8	320	3.1	1	62bps	62bps
25	1:4	160	6.2	2	125bps	167bps
25	1:2	80	12.5	5	250bps	417bps

// Source code for table generator
int main(void)
{
  for (uint8_t rate=RATE_500HZ; rate<RATE_4HZ; ++rate)
  {
    uint32_t hz = RateEnumToHz((expresslrs_RFrates_e)rate);
    printf("| Air Rate | Telem Ratio | Telem Interval (ms) | Packets/second | Bandwidth (no Burst) | Bandwidth (Burst)\n");
    if (rate == RATE_500HZ) printf("|---|---|---|---|---|---|\n");
    for (uint8_t ratio=TLM_RATIO_1_128; ratio<TLM_RATIO_ENUM_MAX; ++ratio)
    {
      uint32_t tlmRatio = TLMratioEnumToValue((expresslrs_tlm_ratio_e)ratio);
      float telemPps = (float)hz / tlmRatio;
      uint32_t telemInterval = 1000 * tlmRatio / hz;
      uint32_t tlmBurst = TELEM_MIN_LINK_INTERVAL * hz / tlmRatio / 1000;
      // Reserve one slot for LINK telemetry 
      if (tlmBurst > 1)
        --tlmBurst;
      else
        tlmBurst = 1;

      printf("%u | 1:%u | %u | %.1f | %u | %.0fbps | %.0fbps\n",
        hz, tlmRatio, telemInterval, telemPps, tlmBurst, telemPps*1/2*5*8,
        5*8*telemPps*tlmBurst/(tlmBurst+1));
    }
  }

  return 0;
}