Subject: Re: silo overflows, was fifo overruns
To: David Jones <email@example.com>
From: Bill Studenmund <firstname.lastname@example.org>
Date: 11/11/1997 19:05:15
On Tue, 11 Nov 1997, David Jones wrote:
> Brad Salai wrote:
> | At 11:43 AM -0800 11/11/97, "Erik E. Fair" (Time Keeper) wrote:
> | >The IPX and SS2 are the fastest stock sun4c systems (40 MHz). If it's still
> | >unusable at 38400, we still have a ways to go.
> | >
> | > Erik <email@example.com>
> | This is bound to sound like a whine, but is not, just a little frustration.
> | I switched from a 16MHz MacII 68020 which had no trouble with 38400 or
> | higher, to a Sparc, to get more speed.
> Same here:
> Amiga 3000 (16 MHz 68030, custom UART, no FIFO, no hardware flow control)
> - Does 38400 no problem.
> Sparc IPC (25 MHz sun4c, zs8530, supposedly 16-character FIFO)
> - Drops characters at 19200.
> The problem is the 8530: it is a very slow part; it must be accessed at
> most once every 2us.
The 8530 is NOT the problem. Mac68k computers use the same part, and
perform quite well. We've supported 38400 w/o hw flow control, and I've
been able to run at 57600 w/ flow control.
2us == 500 kHz. Chip speed isn't a problem here. A royal pain if the
delay's not in hardware, but not this problem.
The problem is that the chip is not getting responded to fast enough.
Something in the system is keeping interrupts locked out for quite a
while. From what I can see of /sys/arch/sparc/include/psl.h, only
splaudio, splstatclock, and splhigh would be higher than the zs hardware
So something's blocking interrupts for too long.