OsmocomBB

Currently we implement data rates starting from 2400 bps and higher, but not 300 bps and 1200/75 bps.
The problem is that those rates are not specified in ITU-T Rec. V.110, which defines 600 bps as the minimum synchronous data rate.

According to 3GPP TS 44.021, section 4.1, the 300 bps user data signalling rate shall be adapted to a synchronous 600 bps stream.
Also, "Incoming asynchronous data is padded by the addition of stop elements" -- this means that we pad bits after stop bit(s):

pad bits = ((600 / 300) - 1) * (start + data + parity + stop)

This logic most likely needs to be implemented in the soft-UART module of libosmocore.git.