[U-Boot-Users] [Q] memtest doubt

[Guennadi Liakhovetski]

Hi Jerry

On Thu, 7 Feb 2008, Jerry Van Baren wrote:

> Guennadi Liakhovetski wrote:
> > Hi all,
> > 
> > looking through the common/cmd_mem.c::do_mem_mtest() function, I couldn't
> > understand the following place:
> > 
> > 		addr_mask = ((ulong)end - (ulong)start)/sizeof(vu_long);
> > ...
> > 		for (offset = 1; (offset & addr_mask) != 0; offset <<= 1) {
> > 			start[offset] = pattern;
> > 		}
> > 
> > why (offset & addr_mask) != 0 and not just offset < addr_mask? Suppose
> > 
> > 	end = 0xbf;
> > 	start = 0;
> > 
> > 	addr_mask = 0x2f;
> > 
> > The loop will iterate over offset = 1, 2, 4, 8, and on 0x10 it will abort
> > and 0x10 and 0x20 will stay untested. Whereas if we just had "offset <
> > addr_mask" it would just function correctly, wouldn't it? Yes, I do realise,
> > that it is at least unusual to set the end address to anything other than
> > start address + ((1 << x) - 1), but still.
> > 
> > Thanks
> > Guennadi
> 
> Hi Guennadi,
> 
> The address test is stepping through the address lines
>   0x01, 0x02, 0x04, 0x08, 0x10, 0x20
> Your end of 0xBF with a mask of 0x2F indicates that the address lines 0x10,
> 0x40, and 0x80 are not present (even though address line 0x80 looks like it is
> part of the test since 0xBF includes 0x80 - but it isn't tested).

I think, you are making a mistake here. Look above how addr_mask is 
calculated:

> > 		addr_mask = ((ulong)end - (ulong)start)/sizeof(vu_long);

That means, it is just calculated based upon your memory range being 
tested. So if for some reason you want to test a strange address range 
like (0x10000) to (0x10000 + 0xbf) then the 0x40 address line will not be 
tested, although it is needed to cover all addresses in this range:-) Or 
am I still missing anything?

Thanks
Guennadi
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Guennadi Liakhovetski