TX serial interface timing too slow at 500kHz

daru commented

2026-07-26 17:02:11 +00:00

Owner

tx_rw bit-bangs the TX module clock/data lines with NOP delays. At 500kHz, each instruction takes 8us. The TX module datasheet requires much faster edges (sub-5ns mentioned in commented-out tx_recover). TX may not register the signals at this speed.

Fix: consider running at higher clock during TX, or using hardware SPI if available.

tx_rw bit-bangs the TX module clock/data lines with NOP delays. At 500kHz, each instruction takes 8us. The TX module datasheet requires much faster edges (sub-5ns mentioned in commented-out tx_recover). TX may not register the signals at this speed. Fix: consider running at higher clock during TX, or using hardware SPI if available.

daru commented

2026-07-27 01:15:44 +00:00

Author

Owner

Likely two issues documented here----one is a likely inefficiency in how we're talking to the TX chip, and the other is the fact that we can't run the tx recover command sequence as defined by the datasheet (pg 288)

time referenced this issue from a pull request that will close it,

2026-08-03 03:59:44 +00:00

feat: TX/RX working — first successful reception via rtl_433 #39

time commented

2026-08-03 04:00:14 +00:00

Contributor

Fixed in PR #39: moved ISR body into main loop (ISR now only reloads timer + sets tick flag), so timing is independent of ISR overhead. Works at 500kHz now.

daru closed this issue

2026-08-03 04:05:06 +00:00

time commented

2026-08-03 04:07:02 +00:00

Contributor

Fixed in PR #39: ISR body moved into main loop (ISR only reloads timer + sets tick flag). Timing is now independent of ISR overhead and works at 500kHz.

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TX serial interface timing too slow at 500kHz #5