Hi,

I am experimenting with a Prolific USB<->RS232 adaptor. We have
in-house developments that need serial communication and there
are more and more mainboards that provide only one RS232 connector.
(We would need more in one machine...)
So we decided to try an usb-serial converter. The one we bought
was happily recognized by a RedHat 9 system but I couldn't get
two-way communication over this converter.
The null-modem cable is working both ways, in fact I tested it
with my machine's two real 16550s.
lsmod shows usbserial and pl2303, dmesg shows this:

usb.c: registered new driver serial
usbserial.c: USB Serial support registered for Generic
usbserial.c: USB Serial Driver core v1.4
usbserial.c: USB Serial support registered for PL-2303
usbserial.c: PL-2303 converter detected
usbserial.c: PL-2303 converter now attached to ttyUSB0 \
(or usb/tts/0 for devfs)
pl2303.c: Prolific PL2303 USB to serial adaptor driver v0.9

I use the attached sources (serial.h, [posix|win32]-serial.c)
in my MinGW/Linux dual platform programs for low-level serial
communication. Here are two testprograms that I used.

serialtest2 just listens and waits for incoming bytes.
If it receives one, the answer is the byte it got + 1.
serialtest1 iterates 10 times writing a byte and expecting
the answer.

I tried using /dev/ttyUSB0 and /dev/usb/ttyUSB0 (chmod was needed
to open them by an ordinary user, open(2) and tcsetattr(3)
succeeded. What I found is that I can write to /dev/ttyUSB0
with serialtest1 and serialtest2 successfully reads it from
/dev/ttyS0. But the answer from serialtest2 cannot be read
by serialtest1. If these programs both use a real serial port
(ttyS0 and ttyS1) the communication is successful both ways.

setserial produces an error:

# setserial /dev/ttyUSB0
Cannot get serial info: Invalid argument

And to be sure:

# setserial /dev/ttyUSB1
/dev/ttyUSB1: No such device

as expected.

I have the kernel-smp-2.4.20-19.9 (not the very latest) errata kernel
and all user space errata packages installed/upgraded.

-- 
Best regards,
Zoltán Böszörményi

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What did Hussein say about his knife?
One in Bush worth two in the hand.