Re: APUS bus access

[<fh...@at...>]

In <Pine.LNX.4.10.10008091645550.416-100000@cassiopeia.home>, on 08/09/00 
   at 04:56 PM, Geert Uytterhoeven <ge...@li...> said:

>On Wed, 9 Aug 2000 hei...@at... wrote:

>Ideally, readl() and friends are meant for _PCI_ memory space only, and
>PCI is per definition little endian.

Hmmm.  So those functions are meant for folks that use PowerMacs? I was
thinking today that those functions had to be OK because APUS drivers must
use them.  Perhaps this is not the case?

>However, the MMIO 53c770 driver currently works on SPARC only. At least
>on SPARC64, you can specify the endiannes of a page in the MMU page
>tables. So on SPARC64, the page tables will be set up such that readl()
>will be little endian on PCI memory space and big endian on SBUS memory
>space. Nice for driver writers, readl() is always correct :-)

I gather the '770 chip is used on an SBUS card and there is a Linux driver
for it then?  I have a rather old version of the 53c770 files that was
made known to me by someone on the APUS list.  Perhaps I should be using
the SPARC version instead.

>I suggest you add

>    #elif defined(CONFIG_APUS)
>    #define readl_l2b(a,b)	in_be32(b,a)
>    ...

If I define that both the PPC and and the '770 chip are big endian then I
don't think that the readl_l2b is defined.  But I will experiment with
using the in_be32 function.

>to sym53c8xx_defs.h (or use le32 if the wiring on the board turns out to
>be different), for clarity.

I really don't want to open my Amiga to see how the '770 chip is wired to
the PPC.   I'm not sure if I could tell by just looking at it anyway.   It
is  most likely possible to find out with a logic probe, since I think the
 endianess is set by wiring some pins with the correct logic values.  At
least I thought I read that somewhere.

>> Is APUS big endian or little endian.  Is M68K Linux big endian or little
>> endian?
>> Am I so confused about this?  Can someone explain it to me?   I always think
>> big endian == m68k, sparc; little endian == intel, alpha.
>> Is the Amiga different?  What is Power Macintosh Linux?

>m68k is big endian
>PPC can be both (PPC had to run NT, sigh), but Linux/PPC is big endian
>MIPS can be both: little endian on e.g. DECstation, big endian on SGI

>> BTW I tried writing 0xee00ff11 to a 32 bit register on the '770 chip and got
>> 0xff11 back.

>And it's a register that allows reading back the same value?

There are three registers, off hand, that should be able to R/W 32 bit
values, they are TEMP, SCRATCHA, and SCRATCHB.  Actually there are a
number of SCRATCHx registers, so probably more than three. 

>OK, so you know at least how to access the least significant short. Now
>you have to find out where the upper part went to, or where it has to go
>to.

Yep.

>Is there any read register for which you can guess what you should read?
>Some chip id or revision number register?

I don't see one by looking in the programming guide, right at the moment.
 
Fred