Why SPI delayed in FSK mode in sx127x?

dernasherbrezon
Thu, 18 Jul 2024 11:19:11 +0000
Hardware

Hi guys,

Several months ago I accidentally stumble across interesting thing: if SPI bus initialised on ~8Mhz, then sx127x chips in FSK mode introduce delay. Cause invalid data transmitted between MCU and sx127x chip.

I did some analysis under different conditions:

LoRa vs FSK mode. LoRa mode seems fine.

Lower SPI frequencies: 2Mhz seems fine, some delay on 4Mhz and more than half tick delay on 8Mhz

Same delay on Heltec V2 (ESP32) and on Ra-02 ( Raspberry PI).

Mitigates only when long run of "1"s is transmitted (0xFF)

Seems like hardware bug? Anyone saw this before?

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