RE: Serial port blues
From: Stuart MacDonald
Date: Sun Jan 21 2007 - 00:32:30 EST
From: On Behalf Of Joe Barr
> I'm forwarding this post by the author of a great little program for
> digital amateur radio on Linux, because I'm curious whether or not the
> problem he is seeing can be resolved outside the kernel.
From: w1hkj [mailto:w1hkj@xxxxxxxxx]
> I am now convinced that the current serial port drivers
> available to us
> on the Linux platform WILL NOT support CW and/or RTTY that is
> generated in a satisfactory manner.
I don't know what FSK/CW/RTTY/BAUDOT is.
> Direct access to the serial port(s) is a kernel perogative in Linux.
> Only kernel level drivers are allowed such port access.
> Until such time as new information becomes available I am going to
> comment out all references to CW and / or FSK via RTS/DTR. I also
> question how useful the FSK on TxD (UART derived) might be to
> most users
> since the 45.45 baudrate is not available in the serial port driver.
> That function will also be commented out.
You may be confusing the old-style baud rate lookup table (B9600 et
al) with the actual capabilities of the serial port. The lookup table
has a limited number of baud rates. You can get more rates than that
using a custom divisor. Most motherboard-based serial ports are
clocked at 1.8432 Mhz. The UART does 16 samples per bit time, yielding
a max baud rate of 115200.
115200 / 25 yields 4608, which is a 1.4% error rate from 4545. This
may or may not be acceptable. 115200 / 2535 yields 45.44, which is a
0.01% error rate, which is likely acceptable.
> Sorry folks, but we win some and lose some.
We make serial port boards with very flexible UARTS. 4545 exactly is
achievable. 45.45 too. Linux supported.
We make multiport serial products.
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