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Date:      Thu, 01 Oct 1998 23:36:23 +1000
From:      "Hallam Oaks P/L list account" <mlnn4@oaks.com.au>
To:        "freebsd-isdn@FreeBSD.ORG" <freebsd-isdn@FreeBSD.ORG>
Cc:        "Andrew Gordon" <arg@arg1.demon.co.uk>
Subject:   Re: HSCX query
Message-ID:  <199810011335.XAA27382@mail.aussie.org>

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>software would use a lot of CPU.   If there is hardware HDLC for the B
>channels but not for the D channel, that would require just the same
>development effort but would have a much less serious impact on
>performance since the average data rate on the D channel is extremely 
>low.

It may seem to unbelievable (but it's true) that it's the opposite way.
There is hardware support for decoding the D channel but not for the B 
channels. As far as the software is concerned, the ASIC is transparent
for the B's in that it just passes through whatever it receives from the
ISAC.

[Note that in my original message I said 'PCI ISAC', but this was a typo;
I meant PCI ASIC. It does the PCI glue functions and also implements the
D channel decoding etc. The ISAC is an ordinary Siemens PSB2186.]

As there's a Linux driver for this card in existance the FreeBSD version 
should not (I hope) be a major problem to get working, but I am stepping 
carefully as I am not an experienced Unix device driver type person.

-- Chris



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