Re: [debian-sparc] Re: SPARC 2.6 serial and console issues
On Sat, 13 Mar 2004, Mike Edwards wrote:
> On Sat, Mar 13, 2004 at 01:15:04AM -0500, Bradley Alexander said:
> > From: Bradley Alexander <firstname.lastname@example.org>
> > I set it up and hung a modem off of it. I can't get the serial port to run
> > at over 9600. I tried running setserial /dev/ttyS0, and it gave me
> > [root@neghvar storm]# setserial /dev/ttyS0
> > /dev/ttyS0, UART: undefined, Port: 0x0000, IRQ: 7574272
> > If I try to define it to spd_vhi (56k modem), that fails too:
> > [root@neghvar storm]# setserial /dev/ttyS0 spd_vhi
> > Cannot set serial info: Invalid argument
> This doesn't surprise me. Our Ultra2 (with a 2.4 kernel) also has an
> 'unknown' UART. setserial on both our Ultra30 and E450 reports a 16450.
That's normal, because setserial 'only' recognizes 8250 and compatible
UART controllers (such as 16450, 1655x, ...), and some mc68000 ones. It
can't recognize the Zilog, because nobody wrote the code for this.
> IIRC, 16450 has a maximum theoretical speed of 9600 bps (might be able to
> get 19200 out of them, but don't quote me on that).
Wrong. I can get up to 115200 bauds with my old and trusty 486dx/25
laptop, over a 16450 UART. If you have a fast enough processor, the 16450
can get up to 115200. The lack of receive buffer is a pain, so in order to
sustain data transfers that fast, your CPU+OS must be able to handle at
least 11520 interrupts per second.
> Suffice it to say, you're not likely to get much more than 9600 bps out of
> the onboard serial ports in your Ultra2. Given the 'unknown' status of the
> UART, you might consider yourself lucky you can even get 9600 bps. <grin>
Sun documentation tells us that the Ultra2 serial port can go as fast as
38400 bauds, and according to the source of the Zilog serial driver,
serial parameters can be changed on the fly, and the max speed is at least
38400 bauds (may be even faster).
How to achieve faster than 9600 bauds is a userland problem. Maybe David
S. Miller (the author of the Linux kernel driver for the Zilog8530), or
SGI users (which seem to have the same serial controller) could tell?
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