SF6 / 125 kHz channel-count test
Measured 2026-09-13. The run stopped on the third packet at the initial four channels: two arrived intact, then the receiver timed out. No five-channel test, lower-channel test, retry or retransmission was performed. Consequently this run does not establish a maximum channel count with 100% reception.
Follow-up: four channels at 5.1 symbols with an IRQ trace stopped at packet 8 and observed no preamble acquisition during the miss.
Requested setup
- Receiver: XIAO ESP32-S3 + WIO SX1262, COM31.
- Reference transmitter: SenseCAP Indicator ESP32-S3 LoRa processor, COM28.
- SF6 / 125 kHz / CR4/5, fixed 32-symbol programmed preamble.
- 4.8-symbol receive visits: 2,457.6 us, rounded up to 2,458 us.
- Buffered 8 MHz SPI and the production fast retune/packet-ownership guards.
- Start at four channels and add one only after 100/100 packets on every channel.
- Stop at the first missing/corrupt packet; USB/reference/scanner faults are reported separately as inconclusive fixture errors.
- 16-byte synthetic payloads at -9 dBm. No identity/channel secrets transmitted.
- Four channel centers: 909.500, 909.750, 910.000 and 910.250 MHz.
- Balanced randomized channel order, seed 606125; varied arrival timing across approximately two idle scan cycles. Arming an expectation does not select the receiver's channel or reset its visit clock.
The 100-packet-per-channel target was not reached: the explicit first-miss stop rule ended the run during its first shuffled pass.
Observations
| Probe | Channel center | Outcome |
|---|---|---|
| 1 | 910.250 MHz | Valid 16 bytes, RSSI -40 dBm, SNR 10.8 dB |
| 2 | 910.000 MHz | Valid 16 bytes, RSSI -40 dBm, SNR 11.0 dB |
| 3 | 909.750 MHz | Receiver timeout; transmitter returned success |
All three transmit acknowledgements and receiver reports matched their sequence IDs, with no missing/replayed/stale USB replies. On the miss, the receiver reported RX mode and zero device errors. The scanner recorded zero retune failures, RX-mode errors, modulation-cache errors or CRC/read errors. No probe was sent on 909.500 MHz before the stop condition.
| Timing | Minimum | Mean | Maximum |
|---|---|---|---|
| Production retune to BUSY low, 3,467 hops | 504 us | 514.652 us | 726 us |
| Idle receive dwell, 3,463 visits | 2,458 us | 2,462.480 us | 2,468 us |
These samples include scanning during the bounded 10-second wait that confirmed the missing packet. There were 2,451 deferred attempts while production preamble/header/packet ownership held a visit; this is not a count of packets or failed retunes. Held visits are excluded from idle-dwell timing. All 3,467 successful retunes used the production fast-RX path.
The means imply about 11.91 ms per four-channel idle cycle, excluding packet-held visits and small loop bookkeeping. Fast retuning alone did not produce 100% reception in this setup. This short stop-on-first-miss experiment does not identify the exact acquisition/phase cause, estimate a stable PER, prove that three channels would pass, or establish a universal board limit.
Implementation and reproduction
This is a lab-only N-channel scheduler over the real tuneProfile() path.
It reuses the two production profile slots as staging slots for the next
frequency. Normal MeshCore radio2 remains two-profile. The explicit test
schedule intentionally does not use the normal two-profile automatic-preamble
fit calculation or generic 6 ms switch / 4 ms loop allowances. It keeps the
existing packet-protection guards and measures real dwell/retune overhead.
python tools/hil/profile_switch_channels.py --receiver COM31 --sender COM28 --output results.json --samples 100 --preamble 32
The controller has regression tests for balanced samples, starting at four, incrementing only after a perfect level, stopping without another TX, and distinguishing fixture failure from an RF miss. A separate RX-only 0.5-second setup check verified the scan timing before any capacity-test packets were sent. The capacity run itself was not repeated.
- Raw result, including the failing probe
- Host controller
- Firmware scheduler
- Harness instructions
- Earlier USB and fast-switch qualification
Build provenance: base commit c329cf1fc1e7f2e8c8733ab0d000094730458fe3
plus the local fast-switch and HIL changes; Arduino ESP32 2.0.17,
Espressif32 6.11.0, RadioLib 7.7.1 pinned at
187ef24791c3d844939b2be13a68bd890bd04e4c. This is the extended V8 harness
with channel_sweep: 1; its binaries differ from the earlier two-profile
V8 measurements, so timings should not be treated as a same-image A/B.
Firmware SHA-256:
- XIAO:
b0a6dd216be8a638fe088219801290d4632afcf63048f8597037650d68cd2301 - Indicator:
f0aa43a46e5e59ebf4768a255bd8c31d7a72c0038e11173314f78908b725786d
Device handoff
After the first-miss stop, both original 8 MiB flash snapshots were restored. Separate full-flash verification matched each backup's digest, followed by hardware reset. The private backups remain in the current-user backup directory. The Indicator RP2040 and RAK4631 were not modified. The interrupted XIAO soak logger remains stopped, and the temporary PlatformIO HIL overlay was removed. Implementation, tests and reports were initially handed off locally before publication.