Software-Based Memory Testing
by Michael Barr
If ever there was a piece of embedded software ripe for reuse it is the memory test. This article shows how to test for the most common memory problems with a set of three efficient, portable, public-domain memory test functions.
[ Introduction | Common Problems | Test Strategy | Data Bus | Address Bus | Device | Put it together ]
This article is from the
book: The test programs for 8051 and Philips XA |
Developing a Test Strategy
Before going on, let's quickly review the types of memory problems we must be able to detect. Memory chips only rarely have internal errors, but, if they do, they are probably catastrophic in nature and will be detected by any test. A more common source of problems is the circuit board, where a wiring problem may occur or a memory chip may be missing or improperly inserted. Other memory problems can occur, but the ones described here are the most common.
By carefully selecting your test data and the order in which the addresses are tested, it is possible to detect all of the memory problems described above. It is usually best to break your memory test into small, single-minded pieces. This helps to improve the efficiency of the overall test and the readability of the code. More specific tests can also provide more detailed information about the source of the problem, if one is detected.
I have found it is best to have three individual memory tests: a data bus test, an address bus test, and a device test. The first two test for electrical wiring problems and improperly inserted chips, while the third is intended to detect missing chips and catastrophic failures. As an unintended consequence, the device test will also uncover problems with the control bus wiring, though it cannot provide useful information about the source of such a problem.
The order in which you execute these three tests is important. The proper order is: data bus test first, followed by the address bus test, and then the device test. That's because the address bus test assumes a working data bus, and the device test results are meaningless unless both the address and data buses are known good. If any of the tests fail, you should work with the board's designer to locate the source of the problem. By looking at the data value or address at which the test failed, he or she should be able to quickly isolate the problem on the circuit board.
[ Introduction | Common Problems | Test Strategy | Data
Bus | Address Bus | Device | Put it together ]
Copyright (c) 2000 by Michael Barr
ESAcademy, 2000
All materials
provided 'as is'
see Disclaimer