Serial port problem/P2/Linux

Serial port problem/P2/Linux

Post by S. John Ilaga » Sat, 27 Feb 1999 04:00:00



I've recently moved to a new Linux box (Dell XPS 400, boots into RH 5.2,
Win98 and WinNT Server) and I'm having a problem with the serial ports.
One port is off the ATX case (9 pin 16550a) and the other is an ISA
Card, 16C650, high-speed serial portt (25 pin) from Byterunner.  I hook
up my ISDN TA (Adtran Express XRT) to the 16C650 card.

The 16C650 card works fine in Win95 and WinNT Server, throughput is in
the 13-15Kbps range.  However, in Linux, it pretty much stinks.  I get
dropped packets constantly and stalled transmissions.  Throughput is
only in the 100bps to 2Kbps range.  I've compiled the kernel with
default serial code and also used patches I've found that modify
serial.c with code that addresses the special FIFO buffers on the 16C650
(location: http://www.devilsthumb.com/~rob)  I've used them before with
great results on my old Cyrix P200+ box.  Also I use irqtune to
reprioritize the irq so that /dev/cua2 (i.e. the 16C650 card which is
DOS COM3) is given the highest priority and of course setserial.  This
exact setup worked great on my old Cyrix box but craps out totally on my
new P2.  Just a default kernel with no mods yields the same results.
Same results also if just using my vanilla 16550A 9 pin serial port
native to the motherboard again with no kernel mods, just setserial.

I'm currently using an internal USR 56K modem w/linux with great speed
and no problems.

Anybody have any suggestions to try?