Hi Greg,
coincidentally, I also tested non-standard baudrates on a PL2303 these
days and was about to start a similar thread when I found this one...
On Fri, 14 Jun 2013 at 18:58, Greg KH wrote:
On Fri, Jun 14, 2013 at 11:20:01AM +0200, Mastro Gippo wrote:
PS: this device (at least mine) WILL support 250K baudrate, as in
windows I can set it in any software I use, and the output is spot
on, measured with a digital oscilloscope.
That's good to know, which model is it? Remember, the pl2303 driver
supports at least 3 generations of this chipset (maybe 4). All of
them seem to work just a little bit differently.
I've tested[1] 250kBaud and even some strange baud rates such as
345678 and 777777 on a PL2303HX based device and got plausible numbers
(same percentage off as nearby standard rates) when measuring the time
it takes to send and receive 1000 bytes after through a RX/TX loop.
This looks to me like at least the HX variant does support arbitrary
baud rates and it definitely doesn't fall back to 9600 as stated in
the comment above the rounding loop.
So, how about starting to get rid of the baud rate list by skipping it
for HX chips only until someone with a type_0 or type_1 devices can
confirm that it works there as well?
BTW, newer revisions of the things that Prolific calls datasheets have
a note next to the baud rate list that says, "For special baud rate
requirements, please contact Prolific FAE for driver customization
support.", which I take as a confirmation that the limit to standard
rates is only imposed by the driver.
BTW2, the open source OSX driver[2] to which Prolific links from their
support page, detects the chip revision, based on the USB device
release number instead of guessing it from other properties of the
device.
cu
Reinhard
[1] As a quick way for testing the capability of the hardware without
having to worry about getting a non-standard baud rate through glibc
and the kernel down to the driver, I hacked the driver to turn a
request for 75 baud into the rate I wanted to test.
[2] http://sourceforge.net/p/osx-pl2303/code/HEAD/tree/trunk
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