[U-Boot-Users] [Q] memtest doubt
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 --- Guennadi Liakhovetski
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).
This is nonsensical with respect to what the address line test is testing (address lines!) and how it is testing them - by stepping through the address lines and looking for inadvertent overlapped memory accesses. Address lines are inherently powers of two, skipping certain ones of them doesn't make much sense, and ending not on a power of two (minus one) doesn't make any sense at all.
I fail to see what your change would benefit as an address line test. If there is a benefit, you will have to rewrite the address line test because having a contiguous mask and a ((2^n) - 1) end is all fundamental to how the address line test works, is fundamental to what address lines are, and is based on the symptoms that are observable when an address line fails. Simply using an arbitrary end address and a funky mask will cause the current test to fail and likely will cause some real failures to be undetected.
Best regards, gvb
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 --- Guennadi Liakhovetski
Guennadi Liakhovetski wrote:
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
Ahh, yes. In your example the 0x80 line isn't tested either, even though it could (and should) be.
The address line test has to be careful to not exceed the end of memory because that is wrong and will cause errors. I think that the problem you are pointing out is that, when we reserve memory space at the end of memory, our "end" address isn't really the memory end address (and rightly so), but the *algorithmic* calculation of the "addr_mask" is not really correct if "end" isn't really the end of memory.
The result is an address line that *could be* (and should be) tested is missed. FWIIW, in similar code I've written in the past, I've hardcoded (#defined) the mask to a sensible value based on my knowledge of the specific hardware. The problem with hardcoding the mask is that it doesn't work with dynamic memory sizing.
Your original question/concept still used the name "addr_mask" which caused confusion on my part. It really should be a length, not a mask. Illustrating with a hand-generated patch, what I am now hearing is the following change:
- addr_mask = ((ulong)end - (ulong)start)/sizeof(vu_long); + len = ((ulong)end - (ulong)start)/sizeof(vu_long); ... - for (offset = 1; (offset & addr_mask) != 0; offset <<= 1) { + for (offset = 1; offset < len; offset <<= 1) { start[offset] = pattern; }
That makes sense to me.
Best regards, gvb
On Thu, 7 Feb 2008, Jerry Van Baren wrote:
Your original question/concept still used the name "addr_mask" which caused confusion on my part.
Ahhh, that's just a variable name:-)
It really should be a length, not a mask.
Of course.
Illustrating with a hand-generated patch, what I am now hearing is the following change:
addr_mask = ((ulong)end - (ulong)start)/sizeof(vu_long);
len = ((ulong)end - (ulong)start)/sizeof(vu_long);...
for (offset = 1; (offset & addr_mask) != 0; offset <<= 1) {
for (offset = 1; offset < len; offset <<= 1) { start[offset] = pattern;That makes sense to me.
Exactly. If everyone agrees, I'll try not to forget to cook up a patch.
Thanks Guennadi --- Guennadi Liakhovetski
participants (2)
-
Guennadi Liakhovetski -
Jerry Van Baren