Re: [Etherboot-developers] NIC file and ROM images

[<ebi...@ln...>]

ke...@us... (Ken Yap) writes:

> >A.2  PnP Option ROM Header
> Offset    Size     Value    Description
> >-----------------------------------------------------
> >00h       BYTE     55h       Signature byte 1.
> >01h       BYTE     AAh       Signature byte 2.
> >02h       BYTE     Varies    Option ROM length in 512-byte blocks.
> >03h       4 BYTES  Varies    Initialization entry point.
> >07h       17 BYTES Varies    Reserved.
> >18h       WORD     Varies    Offset to PCI data structure.
> >1Ah       WORD     Varies    Offset to expansion header structure.
> >
> >So my question is, can we have something like:
> >
> >PnP option ROM Header size 64K
> >512 bytes later, PnP option ROM Header size 64K - 512 bytes
> >512 bytes later, PnP option ROM header size 64K - 1024 bytes.
> >etc.
> 
> Interesting. How about this variation:
> 
> PnP option ROM Header size 512 bytes, jump to start
> PnP option ROM Header size 512 bytes, jump to start
> ...
> PnP option ROM Header size 512+x bytes, jump to start
> start of code (x bytes)
> 
> Problem is the BIOS might be entitled to map in only as much of the ROM
> as the header declares.

I believe it is, the PCI spec says specifically that the ROM must first
be copied into RAM.  And it is legal for us to shorten our ROM image size
after the initialization vector is called.

We read from the ROM ourselves which solves that the too little
information problem.  Another little tidbit is that the PCI data
structure has at offset 15 an indicator byte.  Bit 7 of that byte is
set to 1 if this is the last image, and it is set to 0 if there are
more images.

Eric