digital logic - Which serial protocol or encoding scheme does this scoreboard use?

I am trying to decode a signal stream coming from a Nevco scoreboard controller:

Packets like this are sent every ~2.7 ms.

I suspect it is some sort of UART signal because it is on the RX line of a ATMEGA48, but I cannot identify the finer protocol details like parity and stop bits. All the combinations I have tried returns junk data, so it may be another encoding scheme.

What's unusual is that the same signal is also sent to the MOSI pin of the microcontroller, but there is no clock signal anywhere.

A .vcd file is here.

The shortest pulses (both high and low) are always 8us in length.

This is what two packets look like. Anyone got ideas?