IBM 750GL, 750GX mtspr, mfspr, mtspr, 2.1.4 Thermal-ManagementRegisters (THRMn), 2.1.4.1 Thermal-ManagementRegisters 1–2 (THRM1–THRM2)

User’s Manual

IBM PowerPC 750GX and 750GL RISC Microprocessor

2.1.4 Thermal-Management Registers (THRMn)

The on-chip thermal-management assist unit provides the following functions:

•Compares the junction temperature against user programmed thresholds

•Generates a thermal-management interrupt if the temperature crosses the threshold

•Provides a way for a successive approximation routine to estimate junction temperature

Control and access to the thermal-management assist unit is through the privileged mtspr and mfspr instructions to the four THRM registers.

2.1.4.1 Thermal-Management Registers 1–2 (THRM1–THRM2)

THRM1 and THRM2 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.

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 (see Section 2.1.4.2 on page 79).

Examples of valid THRM1/THRM2 bit settings are shown in Table 2-3on page 79.

TIN TIV

THRESHOLD

Reserved

TID TIE

V

0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
	Bits					Field Name														Description
											Thermal-management interrupt bit. Read only. This bit is set if the thermal sensor output
	0						TIN				crosses the threshold specified in the SPR. The state of this bit is valid only if TIV is set.
											The interpretation of the TIN bit is controlled by the TID bit. See Table 2-3.
	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 2-3.
	2:8				THRESHOLD						Threshold that the thermal sensor output is compared to. The range is 0°–127°C in incre-
											ments of 1°C. Note that this is not the resolution of the thermal sensor.
	9:28					Reserved					Reserved. System software should clear these bits when writing to the THRMn SPRs.
											Thermal-management interrupt direction bit. Selects the result of the temperature com-
											parison to set TIN and to assert a thermal-management interrupt if TIE is set. If TID is
	29						TID				cleared, TIN is set and an interrupt occurs if the junction temperature exceeds the thresh-
											old. If TID is set, TIN is set and an interrupt is indicated if the junction temperature is
											below the threshold. See Table 2-3.
											Thermal-management interrupt enable. Enables assertion of the thermal-management
											interrupt signal. The thermal-management interrupt is maskable by the MSR[EE] bit. If
	30						TIE				TIE is cleared and THRMn is valid, the TIN bit records the status of the junction tempera-
											ture versus threshold comparison without causing an exception. This feature allows sys-
											tem software to make a successive approximation to estimate the junction temperature.
											See Table 2-3on page 79.
											SPR valid bit. Setting this bit indicates that the SPR contains a valid threshold, TID, and
	31						V				TIE control bit. Setting THRM1/2[V] and THRM3[E] to 1 enables operation of the thermal
											sensor. See Table 2-3on page 79.

Programming Model	gx_02.fm.(1.2)
Page 78 of 377	March 27, 2006