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Date: Wed, 3 Oct 2007 14:37:06 +0100
From: Thiemo Seufer <ths@networkno.de>
Subject: Re: [Qemu-devel] U-Boot patch for qemu -M mips
Message-ID: <20071003133706.GM16772@networkno.de>
References: <4702185B.3010807@comsys.ro> <20071002164027.GG16772@networkno.de>
	<470352E7.8050200@comsys.ro>
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To: Vlad Lungu <vlad@comsys.ro>
Cc: qemu-devel@nongnu.org, wd@denx.de

Vlad Lungu wrote:
[snip]
>>>  +long int initdram(int board_type)
>>>  +{
>>>  +       /* Sdram is setup by assembler code */
>>>  +       /* If memory could be changed, we should return the true value 
>>> here */
>>>  +       return MEM_SIZE*1024*1024;
>>>     
>>
>> Qemu gets the amount of RAM passed via a command line switch, the
>> qemu-mips emulation sets up a Linux kernel like "command line" in
>> memory where u-boot could parse it from.
>>
>>   
> Does it, or just when you pass -kernel to it? I'll check.

Hm, you are right, it does that only for -kernel. Would it make sense
to change that in Qemu?

Since the mips_r4k machine doesn't correspond to any real hardware we
have a bit of leeway with the "hardware" design.

>>>  +}
>>>  +
>>>  +
>>>  +int checkboard (void)
>>>  +{
>>>  +       u32 proc_id;
>>>  +
>>>  +       proc_id = read_32bit_cp0_register(CP0_PRID);
>>>  +
>>>  +       switch (proc_id >> 24) {
>>>  +       default:
>>>  +               printf ("Unsupported cpu %d, proc_id=0x%x\n", proc_id >> 
>>> 24, proc_id);
>>>  +       }
>>>  +
>>>  +       return 0;
>>>  +}
>>>     
>>
>> Huh? What is this code good for?
>>
>>   
> Checking for the type of board, I suppose :-)  I think all BSPs have it and 
> it's called early in the boot process. I could either do only a return 0 or 
> actually decode CP0_PRID and print something meaningful, if Qemu sets it to 
> something sensible. Or just print a nice banner.

As it is, this code prints a nice "Unsupported CPU" banner no matter what
(and proceeds anyway instead of bailing out).

Latest CVS Qemu supports a number of different CPUs (see the -cpu switch),
the default for 32 bit is a 24Kf, and for 64 bit a R4000.


Thiemo