Seagate ST15150N Product Manual - Page 22

12 ST15150N/ND/W/WD/WC/DC Product Manual, Rev. D ASA II download code thermal calibration (TCAL) 1. All heads are thermally calibrated at power-up and following SCSI resets before any read or write commands are processed. All heads are also thermally calibrated during the SCSI Rezero Unit command. 2. The drive then delays a fixed period of time (D) before initiating any further thermal calibrations. This delay provides a guaranteed time interval when no thermal calibration interruptions will occur. 3. A single-head TCAL is scheduled to occur every N1 seconds where: N1 = (T - D)/(2 • H) T = Maximum allowable thermal calibration period for any single head (600 seconds) D = Time delay after the power-up/reset calibration before initiating subsequent thermal calibrations (300 seconds) H = Number of heads in the drive (see Section 5.1 "Internal drive characteristics"). 4. After the drive has cycled once through all the heads (H) at the N1 time interval, single-head TCAL scheduling switches to a N2 time interval where: N2 = T/(2 • H). 5. When a single-head TCAL is scheduled, the drive attempts to find an idle period of 25 to 50 milliseconds prior to performing the TCAL. If the TCAL has still not been performed after another N1 or N2 seconds (whichever is the current time interval) the drive forces a TCAL to occur at the next command boundary (even during a read look ahead sequence), and immediately resets the N1 or N2 timer. This guarantees that no head will remain uncalibrated for more than T (600) seconds and that no TCALs will occur closer together in time than approximately N1 or N2 seconds. 6. TCALs performed during the "standard" retry sequence are limited to the failing head, and will be disabled if the host selects a retry count of zero. Refer to Section 11.11 and to the SCSI-2 Interface Product Manual (part number 77738479) for additional timing details.