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User’s Manual
IBM PowerPC 750GX and 750GL RISC Microprocessor
gx_11.fm.(1.2)
March 27, 2006
Performance Monitor and System Related Features
Page 361 of 377
11.9 Checkstops
A checkstop causes the processor to halt and assert the checkstop output pin, CKSTP_OUT. Once the
750GX enters a checkstop state, only a hard reset can clear the processor.
11.9.1 Checkstop Sources
Following is the list of checkstop sources:
• Machine Check with MSR[ME] = 0.
If MSR[ME] = 0 when a machine-check interrupt occurs, then the checkstop state is entered. The
machine-check sources for the 750GX are as follows:
–TEA
assertion on the 60x bus
– Address-parity error on the 60x bus
– Data-parity error on the 60x bus
– Machine-check input pin (MCP
)
– Locked L2 Snoop, with the snoop hit in locked line error enable bit in the L2 Cache Control Register
(L2CR[SHEE]) set
– A parity error in either the instruction tag, data tag, instruction cache, data cache, or L2 tag (if
enabled)
• Checkstop input pin (CKSTP_IN
)
11.9.2 Checkstop Control Bits
Some of the checkstop sources can be controlled via Hardware-Implementation-Dependent Register 0
(HID0) and the L2CR register bits.
Table 11-6. HID0 Checkstop Control Bits
Bits Field Name
Hard
Reset
State
Description
0EMCP0
MCP
pin mask bit
1 Enables MCP
to cause a checkstop if MSR(ME) = 0, or a machine-check inter-
rupt if MSR(ME) = 1.
0 Masks out the MCP
pin. Therefore, the MCP pin cannot generate a machine-
check interrupt or a checkstop. The main purpose of this bit is to mask out fur-
ther machine-check interrupts from MCP
, similar to the MSR(EE) bit for exter-
nal interrupts.
2EBA0
Bus address-parity checking enable
1 Enables an address-parity error to cause a checkstop if MSR(ME) = 0, or a
machine-check interrupt if MSR(ME) = 1.
0 Prevents address-parity checking.
3EBD0
Bus data-parity checking enable
1 Enables a data-parity error to cause a checkstop if MSR(ME) = 0, or a
machine-check interrupt if MSR(ME) = 1.
0 Prevents data-parity checking.
Note: The EBA and EBD bits allow the processor to operate with memory subsystems that do not generate parity. A checkstop latch
is provided in the COP to indicate the checkstop source.