[ixp1200] Re: questions on using the IXP1200 in a PC.

[Scott C. Karlin]

On Mon, Nov 19, 2001 at 03:29:46PM -0800, Joon wrote:
> 
> I understand that it is possible to plug the eval board into the 33-MHz
> 32-bit PCI slot of a standard PC (after some jumper and firmware
> changes). 

Yes, this is true.

> 1. Can the host PC access the SDRAM, SRAM, registers, etc on the
>    IXP1200?

Only the SDRAM plus some PCI registers are accessible from the
host PC.  The SRAM, Scratch Memory, and most other registers
are not accessible.

>    Is using the IXP1200 in the PCI slot of a PC a supported mode of
>    operation in the first place?

It's "weakly supported."  Someone from Intel can chime in here.
The board jumpers allow it to be plugged into an active PCI bus.
There is some documentation from Intel on how to do this.  I will
be posting information on the set-up we use at Princeton to get
an evaluation board to work in a Linux PC.  It does involve
changing the Flash firmware.  Look for details on this list soon.

> 2. Can the StrongArm initiate a DMA transfer directly between its SDRAM 
>    and PC host memory? Any idea what is the rough performance is?

Yes.  I've only made a couple of measurements:
IXP1200 --> Pentium  DMA Push    64-byte block  13.10 MByte/sec
IXP1200 --> Pentium  DMA Push  1500-byte block  49.01 MByte/sec
Pentium --> IXP1200  DMA Pull    64-byte block  11.47 MByte/sec
Pentium --> IXP1200  DMA Pull  1500-byte block  24.66 MByte/sec

I didn't do anything to make it faster.

> 3. Can the StrongArm generate interrupts to the host PC over the PCI bus?

Yes.

> 4. Can we really expand the SDRAM memory on the IXP1200 to 256MB as listed
>    in the specs?

No.  The IXP1200 chip supports upto 256MB.  However the evaluation
board is hardwired at 32 MByte.

Scott