5. IDE Command Descriptions
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When a write type command is issued, the IO16 Enable and Data Request are set. After
the data to be written is put into the RAM buffer the BSY flip-flop is set. This can be
done only when the buffer is full in write mode and it is not the last transfer. Write type
commands include Write Sector(s), Format, and Write Sector Buffer.
A drive can respond properly to a command only when the drive microprocessor is
active. When BSY is active the drive has read and write access to the command block
registers. The host, however, can read only the status register and alternate status
register. Any attempted host read of a command block register while BSY is active
results therefore in a read of the status register instead. The BSY latch can be cleared
only by the drive microprocessor, which can set or reset the BSY flip-flop. When BSY is
inactive the host has read and write access to all command block registers.
Data Retry Algorithm
When an ECC error is detected in the data field during a read operation, the retry
algorithm shown in the following table "Data Retry Algorithm" is used.
Step 1
read retry
Step 2
read retry
Step 3
read retry
Step 4
apply ECC to Step 3
Step 5
read retry with +65 micro inch offset
Step 6
apply ECC to Step 5
Step 7
read retry
Step 8
apply ECC to Step 7
Step 9
read retry with -65 micro inch offset
Step 10
apply ECC to Step 9
Step 11
read retry
Step 12
read retry
Step 13
read retry
Step 14
read retry
Step 15
read retry
Step 16
read retry
In the event of a hard error steps 1-16 are repeated eight times for a total of 128 retries.
Allowing 17 ms for each read retry and 75 ms for each ECC correction, the total time is
4.0 seconds (17 ms * 12 * 8 + 75 ms * 4 * 8 = 4032 ms) to return a non-recoverable
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