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dual ported ram device driver virtual memory

physical memory

From: robertl@localhost.localdomain (Robert Lipe)
Subject: Re: KERNEL PANIC when my Device Driver accesses hardware
References: <3c2eb8eb.29083668@news.bigpond.com> 
Date: Sun, 30 Dec 2001 14:01:10 GMT

[ followup-to set to c.u.s.p.]

On Sun, 30 Dec 2001, Bob Morrison <rmorrison1@bigpond.com.au> wrote:

>I have run into a brick wall while attempting to write a device driver
>to access a hardware adaptor which uses a 1k block of dual port ram
>located at address 0x0CA000.

It can be done.

>I have determined, using printf statements, that the driver is
>receiving the correct hardware address. 
>
>However, a kernel PANIC occurs any time an attempt is made to read or
>write to the hardware adaptor's addresses.

Your code samples below show that you're reading the adapter's physical
address, not a virtual one.   You need a virtual address for these accesses.


>The software environment is SCO 3.2v4.2 with development system.
>The hardware is clone Pentium.

Part of me wonders why you're developing on an OS that was obsolete 
almost seven years ago, but I won't dwell on that now, since the answer
is the same for current OpenServer, too.

>I have not been able to obtain access to a copy of SCO's device driver
>writers manual which is clearly what I need. Nevertheless, I have got
>this far with the following publications:

Fortunately, most of what you need is available on line.   The Hardware
Developer Kit (HDK) is available online at: 
        http://www.sco.com/developers/hdk/
While it's less than intuitive, goto:
        http://www.sco.com/support/docs/
and folow OpenUNIX 8 (the HDK doc set between OpenServer, UnixWare, 
and OpenUNIX is unified, but the OpenServer entry point on the web is 
"broken") and follow hardware and driver development.

>a). "Writing a UNIX Device Driver" , Janet I. Eagan & Thomas
>J.Teixeira published by Wiley, &
>
>b). "Writing UNIX Device Drivers", George Pajari, published by Addison
>Wesley.
>
>Both books have provided almost all that was needed up until now.

The FAQ for c.u.s.p. lists a few others, too.

>However, while Pajari's book deals specifically with SCO UNIX, he
>makes only passing reference to the fact that some adaptor cards might
>access dual port memory.

I recall that outtage.   I think I also recall a chapter or two that
was missing in my copy. ;-)

>The first mentioned book appears to explain how to do it, but the
>method does not seem to suit SCO UNIX.  

Correct.  This is one of the corners of device driver programming that's
different in all OSes.  (Well, except in UDI where udi_pio_map is exactly
the same in all OSes....)

>    int     symax_addr      =       SYMAX__0_SCMA;
>.
>struct mailbox *MB;     /* hardware data structure defined earlier */
>.
>.   
>MB = (struct mailbox * ) symax_addr;  /* Get the Hardware address */
>
>MB->nim_parameters = restart;         /* Reset the SyMax card */
>.
>.
>==============================================
>Clearly there is something important missing here.
>Any assistance would be greatly appreciated. 

You need to pass that physical address to sptalloc to get a mapped virtual
address.   So that is approximately like:

        MP=sptalloc(1, PG_P | PG_PCD, btoc(symax_addr), NOSLEEP);

You also probably need to tag this identifier as volatile to stop the
optimizer from getting clever on your hardware accesses.   AFAIR, that
version of the optimizer is too stupid to get too ambitious in this 
regard, but making accesses through MB volatile will save you grief.

RJL

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