FEAT | TNC over SPI #48
Description
🚀 Feature Proposal
Have MeshTNC act
- as an SPI peripheral to the controller (say, a raspi), speaking TNC in some useful framing that fits SPI
- as an SPI controller to the LoRa chip (assuming it uses SPI, like most do)
So that devices in which SPI is available for addon hardware but serial is not, can speak to LoRa radios over SPI.
Motivation
Some devices (Lorawan/Helium gateways) have mini PCIe slots that expose SPI and maybe one more pin. To conveniently use an SX1262 with software like pyMC_Repeater, we need 3 more pins (RST, IRQ/DIO1, BUSY). But MeshTNC can be used by pyMC_Repeater over just 2 pins (serial), if I pretend flow control is not a thing. However, a raspi (which is in most of those gateways) cannot do HW UART over all SPI pins. While SW UART might work, I don't think it is very clean.
SPI, meanwhile, has built-in framing (even if that's a solved problem in TNC), so it seems like an interesting fit for the protocol. Between (say) pyMC_Repeater and MeshTNC, we'd need exactly 4 pins (MISO/MOSI/CLK/CS), and between MeshTNC and (say) SX1262, we can wire whatever pins we need on a single addon board.
This thought is not entirely finished. Questions and further thoughts very welcome.