2-24
MPC7400 RISC Microprocessor Users Manual
The MPC7400 Processor Register Set
Control and access to the thermal management assist unit is through the privileged
mtspr
/
mfspr
instructions to the three THRM registers. THRM1 and THRM2, shown in
Figure 2-12, 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 THRM1 or THRM2.
Figure 2-12. Thermal Management Registers 1D2 (THRM1DTHRM2)
The bits in THRM1 and THRM2 are described in Table 2-13.
Table 2-13. THRM1DTHRM2 Bit Settings
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 THRM1 and
THRM2 to 0, and restarts the comparison if THRM3[E] is set.
Bits
Field
Description
0
TIN
Thermal management interrupt bit (read-only). This bit is set if the thermal sensor output crosses
the threshold speciTed in the SPR. The state of TIN is valid only if TIV is set. The interpretation of
TIN is controlled by TID. See Table 2-14.
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 2-14.
2D8
Threshold
Threshold that the thermal sensor output is compared to. The range is 0D127 C, and each bit
represents 1 C. Note that this is not the resolution of the thermal sensor.
9D2
8
Reserved. System software should clear these bits when writing to the THRM
n
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 2-14.
30
TIE
Thermal management interrupt enable. The thermal management interrupt is maskable by the
MSR[EE] bit. If TIE is cleared and THRM
n
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 2-14.
31
V
SPR valid bit. Setting this bit indicates the SPR contains a valid threshold, TID and TIE controls
bits. THRM1[V] = 1, THRM2[V] = 1, and THRM3[E] = 1 enables the thermal sensor operation. See
Table 2-14.
TIV
THRESHOLD
0
1
2
8
9
28 29 30 31
TID
TIN
Reserved
TIE V
ê ê 0 0 0 êê0 0 0 0 êê0 0 0 0 êê0 0 0 0 êê0 0 0 0 êê0 êê