Technical data

3-32 Computer Group Literature Center Web Site
Test Descriptions
3
ACC - Device Access
Command Input
PPCx-Diag>eide acc
Description
The ACC test performs five non-data EIDE commands: NOP, EXECUTE
DEVICE DIAGNOSTICS, RESET, IDENTIFY DEVICE, and SEEK. The
test is non-destructive since data is not read from or written to the disk
itself. Data integrity of the disk is not altered.
The BSY bit in the status register is first checked to verify that the device
registers are valid (provided a device is attached). If a time-out occurs
while waiting for a “ready” condition, the test aborts and an error is
reported. Otherwise, a short walking bit test is performed followed by
execution of the following five commands:
1. NOP.
“NOP” forces an abort error condition, setting the ERR bit in the status
register and the ABORT bit in the error register. The test ensures that this
condition occurs.
2. EXECUTE DEVICE DIAGNOSTICS.
“EXECUTE DEVICE DIAGNOSTICS” forces pre-determined values
into cylinder high, cylinder low, error, sector count, sector number, and
device/head registers. These values are compared to expected values.
Allowances are made for differences between ATA drives and ATAPI
CD-ROM dirves.
3. RESET
“RESET” performs two functions: it tests the reset bit of the Device
Control register and establishes known device signatures. Once the device
signature is in place, the correct interface protocol (ATA or ATAPI) may
be invoked.