[Enhancement] Raw HDLC stream driver

[IW3IJQ]

During the golden age of Packet Radio the radio interface consisted of a modem connected to a Z80-SIO, as in TNC2, or the same type of modem connected to a Z8530 SCC, as in PA0HZP OptoPcScc or SuperVozelj multiport node. ​ Some multiport nodes are still active with high-speed modems (38k4, 76k8, 1M2 bps). These modems carry a raw bitstream from/to the HDLC controller (Z80-SIO/Z8530). There are not many alternative controllers with modern hardware, and this can be a problem if the CPU board fails.

It might be interesting to interface the raw bitstream of these modems with the DireWolf HDLC controller using Raspberry GPIOs, or via USB with an RP2040 or an FT234.