I posted these original questions, and I received a series of e-mails
that I will try to summarize.
In article <1993Jan27.061108.15132@tgivan.wimsey.com> mak@tgivan.wimsey.com writes:
>It's time for a bleary eyed dump of some questions I'm interested in
>hearing answered. These focus on some thought experiments about the
>(Sun/sparc) serial ports. I'm assuming outbound modem i/o in all cases below.
>
>(I hope these questions aren't too cryptically worded.)
>
> * stty says: raw, clocal, cread. Will this CPU interrupt per character?
Always get interrupts per char on the built in serial ports. In fact when
continuous at 19.2, the perfmeter's interrupt display is quite convincing
thereof.
>
> * tty interrupt priority vs. SCSI bus interrupts. How do they
> compare logically?
>
Both h/w and s/w interrupt on the built ins are much higher than the SCSI.
> * how much write(2) i/o before get flow control from serial device,
> not the DCE.
I personally did not find the limit. But I was not looking too hard. I
know I threw a lot of data at 19.2 DTE (each approx. 1k writes) when the
modem speed was in 9.6. In general, I'm told that the STREAMS driver can
get full, as a function both of messages and their aggregate size. But
with such a slow device, and such small buffers used, I couldn't see
flowcontrol in my meager little tests.
>
> * does the device driver dma (written) data onto the serial line
> driver/chip.
>
Not the built in serial ports, of course. I asked that question because I
was confused about some includes I found. The Sbus MCP (e.g.,) 8::1
probably does DMA. Those aforementioned include files show dma buffers and
sizes. There are other SCSI terminal servers, that i learned about in this
process. These servers can interrupt upon SCSI packet "xmit", but
don't interrupt otherwise.
= Mak
P.S. Thanks and gratitude to Guy Harris, and to Cendata's support people,
including Dennis Cronin and Vic Serbe.
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