This test detects these memory faults:
- Address Line: The board or chip address lines are shorting or stuck at 0 or 1. Either condition could result in errors when the hardware reads and writes to the memory location. Because this error occurs on an address line, the data may end up in the wrong location on a write operation, or the hardware may access the wrong data on a read operation.
- Data Line: The board or chip data lines are shorting or stuck at 0 or 1. Either condition could result in corrupted values as the hardware transfers data to or from memory.
- Retention: The contents of a memory location change over time. The effect is that the memory fails to retain its contents over time.
The Walking Ones test includes four sub-tests:
- Walking Ones: This subtest first initializes memory to all zeros. Then the subtest writes, reads, and verifies bits, with each bit successively set from the least significant bit ( LSB) to the most significant bit ( MSB). The subtest configures bits such that by the time it sets the MSB, all bits are set to a value of 1. This pattern repeats for each location within the memory range that you specify. For example, the values for a byte-based Walking Ones subtest occur in this order:
0x01, 0x03, 0x07, 0x0F, 0x1F, 0x3F, 0x7F, 0xFF
- Ones Retention: This subtest immediately follows the Walking Ones subtest. The Walking Ones subtest should leave each memory location with all bits set to 1. The Ones Retention subtest verifies that each location has all bits set to 1.
- Walking Zeros: This subtest first initializes memory to all ones. Then the subtest writes, reads, and verifies bits, with each bit successively set from the LSB to the MSB. The subtest configures bits such that by the time it sets the MSB, all bits are set to a value of 0. This pattern repeats for each location within the memory range that you specify. For example, the values for a byte-based Walking Zeros subtest occur in this order:
0xFE, 0xFC, 0xF8, 0xF0, 0xE0, 0xC0, 0x80, 0x00
- Zeros Retention: This subtest immediately follows the Walking Zeros subtest. The Walking Zeros subtest should leave each memory location with all bits set to 0. The Zeros Retention subtest verifies that each location has all bits set to 0.