Bug in 1.94 with 38k

[AgentFriday]

There is a 128 byte internal hardware buffer for both send and receiver (256 total).  This is a limitation of the WiFi module (ESP8266) itself.  What do you mean by "watermark"?

I think the proper term is high-water mark... Just a threshold that activates packetization.  If non-zero time is required to make room in the buffer, then the process would need to be started soon enough that the buffer pressure is relieved before it overflows.

Does your driver recognize when CTS is asserted to stop sending of data from the C64 to the modem?  That occurs when the buffer is full.

Yes, the 38k driver is fully responsive to the CTS line, and if used properly should be able to throttle outgoing data indefinitely without loss.