Seagate ST31250N Product Manual page 22

12 Barracuda 2LP Product Manual, Rev. D
during format, at Re-Zero command, at spindle-up, during read-error recov-
ery, and during reassign-block functions). You can use the Re-Zero com-
mand to reset the thermal compensation timer to let the host know when the
interruption for thermal compensation will occur.
ASA II thermal calibration
At power up and following a SCSI reset, the drive calibrates the heads using
the SCSI Rezero Unit command before processing read and write com-
mands. The drive then delays a fixed period of time (D) before performing any
additional thermal calibrations. This ensures a specific time interval when no
thermal calibration interruptions will occur.
After the delay interval (D) expires, a single head thermal calibration (t-cal)
is scheduled every N1 seconds. Refer to the equation below.
N1 = (T - D) / (2 * H)
T = 600 seconds (the maximum allowable thermal calibration period for any
single head)
D = 300 seconds (period after the power-up/reset calibration before initiating
subsequent thermal calibrations)
H = Number of heads in the drive
After the drive has cycled once through all of the heads (H) at the N1 time
interval, the scheduling of single head thermal calibrations switches to an N2
time interval. Refer to the equation below.
N2 = T / (2 * H)
When a single head thermal calibration is scheduled, the drive attempts to
find an idle period of 25 to 50 milliseconds prior to performing the thermal
calibration. If the thermal calibration has not been performed after another N1
or N2 seconds elapse (whichever is the current time interval), the drive forces
a thermal calibration to occur at the next command boundary (even during
a read lookahead sequence), and immediately restarts the N2 or N2 second
timer–this guarantees that no head will remain uncalibrated for more than T
seconds and that no thermal calibrations will occur closer together in time
than approximately every N1 or N2 seconds.
Any thermal calibration performed during the standard retry sequence will be
limited to the misaligned head, and will be disabled if the host has selected
a retry count of zero.