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Control and access to the thermal management assist unit is through the privileged
mtspr/mfspr instructions to the three THRM registers. THRMI and THRM2, shown in
Figure 2-10, provide the ability to compare the junction temperature against two
user-provided thresholds. Having dual thresholds allows thermal management software
differing degrees of action in reducing junction temperature. Thermal management can use
a single-threshold mode in which the thermal sensor output is compared to only one
threshold in either THRMI or THRM2.
~
Reserved
THRESHOLD
o
1
2
8
9
28 29 30 31
Figure 2-10. Thermal Management Registers 1-2 (THRM1-THRM2)
The bits in THRMI and THRM2 are described in Table 2-15.
Table 2-15. THRM1-THRM2 Bit Settings
Bits
Field
Description
0
TIN
Thermal management interrupt bit. Read-only. This bit is set if the thermal sensor output crosses
the threshold specified in the SPR. The state of TIN is valid only if TIV is set. The interpretation of
TIN is controlled by TID. See Table 2-16.
1
TIV
Thermal management interrupt valid. Read-only. This bit is set by the thermal assist logic to
indicate that the thermal management interrupt (TIN) state is valid. See Table 2-16.
2-8
Threshold Threshold that the thermal sensor output is compared to. The range is 0°-127° C, and each bit
represents 1 ° C. Note that this is not the resolution of the thermal sensor.
9-28
-
Reserved. System software should clear these bits when writing to the THRMn SPRs.
29
TID
Thermal management interrupt direction bit. Selects the result of the temperature comparison to
set TIN and to assert a thermal management interrupt if TIE is set. If TID is cleared, TIN is set and
an interrupt occurs if the junction temperature exceeds the threshold. If TID is set, TIN is set and
an interrupt is indicated if the junction temperature is below the threshold. See Table 2-16.
30
TIE
Thermal management interrupt enable. The thermal management interrupt is maskable by the
MSR[EE) bit. If TIE is cleared and THRMn is valid, the TIN bit records the status of the junction
temperature vs. threshold comparison without causing an exception. This lets system software
successively approximate the junction temperature. See Table 2-16.
31
V
SPR valid bit. Setting this bit indicates the SPR contains a valid threshold, TID and TIE controls
bits. THRM1/2[V)
=
1 and THRM3[E)
=
1 enables the thermal sensor operation. See Table 2-16.
If an mtspr affects a THRM register that contains operating parameters for an ongoing
comparison during operation of the thermal assist unit, the respective TIV bits are cleared
and the comparison is restarted. Changing THRM3 forces the TIV bits of both THRMI and
THRM2 to 0, and restarts the comparison if THRM3[E] is set.
2-22
MPC750 RISC Microprocessor User's Manual
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