One issue that vexed me was that there seemed no way to find out how many characters were remaining in the USB to Serial chip's buffer.
When closing the device, the Linux driver will drain the Linux buffer then wait a fixed time  for the device FIFO to drain. The time was enough for when 9600 or higher was used but not at 110 Bd.
The result was that the output was cut off (atr low baud rates) unless an artificial delay was added..  something like...
( cat myText.txt; sleep 10 ) > /dev/ttyUSB0

On Fri, Dec 10, 2021 at 9:53 PM ad7i <ad7i@ad7i.net> wrote:
I basically have running what I described in my feature set.  I use an AVR MCU to suck in the ASCII at 9600 from the USB to Serial bridge chip, and then interrupt drive a process to bit bang out the 5 unit Baudo code on a pin port.  That all works great.   My problem is that there's something whacky that I don't understand about the USB drivers (W10 and Linux) for USB to serial bridge chips like the CP210x and CH340x.  In some cases the system will respect XonXoff flow control but not RTS/CTS and in others it is RTS/CTS but not XonXoff and in a third case it will respect neither.  I can see by using RealTerm that XonXoff are being sent and received to/from the AVR MCU, and that Realterm responds correctly to CTS from the MCU.  And yet, when using some W10/Linux application to send data to the USB port the computer will not respect flow control commands from the AVR MCU, causing FIFO overflows on the MCU.  Since I can't figure out what's wrong with the flow control mechanisms in the drivers or OS, my solution has been to move to the AVR128DB32, which provides for 16 Kbytes of RAM.  With 16Kbytes of RAM in the MCU, I can hold a lot of TTY pages of print in RAM before things go bad.

Paul, ad7i


On Fri, Dec 10, 2021 at 8:52 PM Michael Katzmann <vk2bea@gmail.com> wrote:
I worked to get the Linux kernel driver to work at arbitrary baud rates on the Prolific PL2303A-TA USB to serial chip.

This can do 5 bit / 1.5 stop / 45 baud with the linux driver although the chip can actually get closer to 45.45 Bd if you want to tweak the driver. (the linux ioctl call (termios2 structure) only handles integer bit rates)


This chip is used in this USB to serial device (and many others) https://www.amazon.com/Sabrent-Converter-Prolific-Chipset-CB-DB9P/dp/B00IDSM6BW
 
I was using it with the ASR33 (110 Bd) but did check the 45 Bd use. As with the 33 you will need to go from RS232 to current loop.

Michael   NV3Z / VK2BEA / G4NYV

On Fri, Dec 10, 2021 at 1:38 PM chris johnson <archangel_cpj@hotmail.com> wrote:
Anyone making a batch of adaptors for usb to model 15 use????  Or have any already made for sale????
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