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More README fixes.

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Martin Whitaker 2020-05-24 22:02:51 +01:00
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@ -211,38 +211,35 @@ Please be aware that not all errors reported by PCMemTest are due to bad
memory. The test implicitly tests the CPU, caches, and motherboard. It is
impossible for the test to determine what causes the failure to occur. Most
failures will be due to a problem with memory. When it is not, the only option
is to replace parts until the failure is corrected.
is to replace parts until the failure is corrected.
Once a memory error has been detected, determining the failing module is not a
clear cut procedure. With the large number of motherboard vendors and possible
combinations of memory slots it would be difficult if not impossible to assemble
complete information about how a particular error would map to a failing memory
module. However, there are steps that may be taken to determine the failing
module. Here are three techniques that you may wish to use:
module. Here are some techniques that you may wish to use:
1) Removing modules
* Removing modules
* This is the simplest method for isolating a failing modules, but may only
be employed when one or more modules can be removed from the system. By
selectively removing modules from the system and then running the test
you will be able to find the bad module(s). Be sure to note exactly which
modules are in the system when the test passes and when the test fails.
This is the simplest method for isolating a failing modules, but may only
be employed when one or more modules can be removed from the system. By
selectively removing modules from the system and then running the test
you will be able to find the bad module(s). Be sure to note exactly which
modules are in the system when the test passes and when the test fails.
* Rotating modules
* When none of the modules can be removed then you may wish to rotate modules
to find the failing one. This technique can only be used if there are three
or more modules in the system. Change the location of two modules at a time.
For example put the module from slot 1 into slot 2 and put the module from
slot 2 in slot 1. Run the test and if either the failing bit or address
changes then you know that the failing module is one of the ones just moved.
By using several combinations of module movement you should be able to
determine which module is failing.
2) Rotating modules
When none of the modules can be removed then you may wish to rotate modules
to find the failing one. This technique can only be used if there are three
or more modules in the system. Change the location of two modules at a time.
For example put the module from slot 1 into slot 2 and put the module from
slot 2 in slot 1. Run the test and if either the failing bit or address
changes then you know that the failing module is one of the ones just moved.
By using several combinations of module movement you should be able to
determine which module is failing.
3) Replacing modules
If you are unable to use either of the previous techniques then you are
left to selective replacement of modules to find the failure.
* Replacing modules
* If you are unable to use either of the previous techniques then you are
left to selective replacement of modules to find the failure.
Sometimes memory errors show up due to component incompatibility. A memory
module may work fine in one system and not in another. This is not uncommon
@ -297,7 +294,7 @@ It should be obvious that this strategy requires an exact knowledge of how the
memory cells are laid out on the chip. In addition there is a never ending
number of possible chip layouts for different chip types and manufacturers
making this strategy impractical. However, there are testing algorithms that
can approximate this ideal strategy.
can approximate this ideal strategy.
## PCMemTest Test Algorithms
@ -310,12 +307,12 @@ inversions. The moving inversion tests work as follows:
1. check that the pattern has not changed
2. write the pattern's complement
3. increment the address
4. repeat 2.1 to 2.3
4. repeat 2.i to 2.iii
3. Starting at the highest address
1. check that the pattern has not changed
2. write the pattern's complement
3. decrement the address
4. repeat 3.1 - 3.3
4. repeat 3.i - 3.iii
This algorithm is a good approximation of an ideal memory test but there are
some limitations. Most high density chips today store data 4 to 16 bits wide.
@ -335,12 +332,12 @@ caching or buffering. The algorithm works as follows:
1. For starting offsets of 0 - 19 do
1. write every 20th location with a pattern
2. write all other locations with the pattern's complement
3. repeat 1.2 one or more times
3. repeat 1.ii one or more times
4. check every 20th location for the pattern
This algorithm accomplishes nearly the same level of adjacency testing as
moving inversions but is not affected by caching or buffering. Since separate
write passes (1.1, 1.2) and the read pass (1.4) are done for all of memory we
write passes (1.i, 1.ii) and the read pass (1.iv) are done for all of memory we
can be assured that all of the buffers and cache have been flushed between
passes. The selection of 20 as the stride size was somewhat arbitrary. Larger
strides may be more effective but would take longer to execute. The choice of
@ -396,7 +393,7 @@ In each memory region in turn, and for each pattern in turn, uses the moving
inversions algorithm with patterns of a random number and its complement. The
random number is different on each test pass so multiple passes increase
effectiveness.
### Test 6 : Moving inversions, 32/64 bit pattern
In each memory region in turn, and for each pattern in turn, uses the moving