sandy@turnkey.TCC.COM (Sanford 'Sandy' Zelkovitz) (11/17/88)
The following program was uploaded to my BBS which I though my interest all
users of Microport System V/AT!
Sanford <sandy> Zelkovitz XBBS 714-898-8634
----------------------- cut/snip/whatever here ------------------------------
/******************************************************************************
16550
a utility that iturns on the FIFO of a NS 16550 chip
by John Welch, of Igloo Computers
Public Domain Software
Hobbyists, feel free to use, abuse, pirate and re-distribute this program.
Commercial use prohibited without consent of the author.
Send fan mail to jjw@igloo
Send flames to jjw@/dev/null
******************************************************************************/
#include <sys/types.h>
#include <sys/io_op.h>
#include <fcntl.h>
int fd;
void outb();
extern int errno;
main()
{
/*
I've waded through the NS 16550 docs for several days now,
and what follows seems accurate enough.
At any rate, the basic idea is that a 16550 with FIFO enabled
has (*FINALLY!*) cured igloo's problems with losing newsfeeds. I
thought I'd make this available to the net in the hopes that it may
help other people who've been singing the 'microport lost character
blues.' As microport has been unable to cure this, we finally fixed
it ourselves. By the way, if you aren't tech-y, this may bore you
to death. I've got it written to patch tty0 and tty1, and since on a
16450 or earlier this register isn't writable it should cause no
problems. Just un-shar it by typing
sh 16550.shar
and compile this with
cc -o 16550 -O 16550.c
It might be a good idea to chmod this to 700, to prevent users from
flushing the buffers on you. Adding this to the inittab file or some
such place should be all thats needed. Run it once at boot-up and
forget it.
A bit of history here: Microport's serial port drivers are
brain-dead. Apparently the problem is with the high-water mark in
the kernel, and so it's *not* fixable with new drivers. What this means
is that you lose characters sometimes. It is particularly noticable
while doing a 9600-baud newsfeed on one serial line while another
user on the other line is cat-ing a text file at 300 baud. Usually
when this happens, you get many errors during the newsfeed and as
often as not you lose the feed altogether. Microport has been told of
this problem many times, and they've piddled and fuddled and moped
around trying to fix it. At first they said we should get faster
hardware because an 8Mhz AT couldn't handle 9600 baud. Fine, we found
a place that loaned us a 20Mhz 0-wait 4Mbyte 386 board for a weekend.
Guess what??? The problem was just as bad as before. Then they sent
us new driver to install, which did not help the problem. They then
suggested that we need a smart serial card, to the tune of around
$1500 or so. They think that 9600 baud cannot be done on these machines.
That's bull-squat, folks! XENIX does 9600 baud just fine. Microport is
unable and unwilling to fix this problem. We had to explore alternate
ways of doing it ourselves, preferrably without costing us hobbyists
an arm and a leg. We feel we've found an acceptable solution with the
16550 UART chip.
The 16550 is a half-way step between a 'smart' serial card
and the usual 16450-type 'dumb' card. Using the FIFOs in the 16550
can not only prevent lost characters, but can result in more efficient
CPU utilization, with less time wasted in processor overhead to read
each character sent. It does this by a device called a FIFO buffer, a
First-In, First-Out scheme. When receiving characters, the 16550 will
only interrupt the CPU when one of two events happens: When enough
characters have been received (you can define 'enough' to be 1, 4, 8
or 14) or when at least 1 character has been received and there has
not been another character come through for 4 times the time 'width'
of a character. In this manner, when the CPU finally gets interrupted,
much more data can be dumped to the CPU at once, cutting down on all
the overhead involved in context-swiching and so forth.
In addition, if the CPU takes too long to read the FIFO, the
16550 will send its own flow-control to throttle back the incoming
data, preventing buffer over-runs that have plagued microport from day
one.
The 16550 chip is a drop-in replacement for the 16450, and it
costs about $25 or so (not much more than the 16450). With this chip
and a trivial amount of software, you can not only cure microports
brain-dead serial device driver problems, but you can also enjoy most
of the benefits of a 'smart' card with very little cost.
What follows is an explaination of what this program does and
why it does it. If you have multi-port 'dumb' boards with 8250's,
16450's or whatever, you *should* be able to replace those chips with
16550s and modify this program to set (base+2) for each port.
tty0's base address is 3f8. The FIFO control register is at
base+2 (3fa). The byte written at this address is defined as follows:
Bits 7 & 6 define at what level the 16550 interrupts the CPU. 11 is 14
bytes deep, 10 is 8 bytes deep, 01 is 4 bytes deep and 00 is 1 byte deep
Bits 5 & 4 are not used, so I set them to 00.
Bit 3 defines the performance of some pins that are not used on the
16450, so it's not likely to be of consequence to anything we do. I've
chosen to keep them performing the way a 16450 would, setting this bit
0.
Bit 2 clears and resets the transmit FIFO.
Bit 1 clears and resets the Receive FIFO.
Bit 0 turns the FIFO buffering on.
To turn on the FIFO at tty1 to a 4-byte level, one should
write a 0x47 to port 0x2fa. To set tty0 at the maximum FIFO level,
send 0xc7 to port 0x3fa. To disable FIFOs at tty1 send 0 to 0x2fa.
*/
if ((fd = open("/dev/mem",O_RDWR)) == -1) /* open mem dev for read/write */
{
perror("Open /dev/mem");
exit(1);
}
outb(0x3fa,0x87); /* this turns on tty0's FIFO, 8 characters deep */
outb(0x2fa,0x87); /* this turns on tty1's FIFO, 8 characters deep */
close(fd); /* all done setting up FIFOs. */
}
void outb(portno, data)
int portno;
unsigned char data;
{
io_op_t iop;
iop.io_port = portno;
iop.io_byte = data;
errno = 0; /* clear error indicator */
ioctl(fd, IOCIOP_WB, &iop); /* write the data to that port */
if (errno)
printf("Error setting port %04x\n",portno);
/* send to stdout so they can re-direct easier */
}