Compaq EV68A specifications Exception Summary Register Excsum, Mchkd W1C, Fbtp W1S

Ibox IPRs

Table 5–8describes the hardware interrupt clear register fields.

Table 5–8 Hardware Interrupt Clear Register Fields Description

Name	Extent	Type	Description
Reserved	[63:33]	—	—
SL	[32]	W1C	Clears serial line interrupt request
CR	[31]	W1C	Clears corrected read error interrupt request
PC[1:0]	[30:29]	W1C	Clears performance counter interrupt requests
MCHK_D	[28]	W1C	Clears Dstream machine check interrupt request
Reserved	[27]	—	—
FBTP	[26]	W1S	Forces the next Bcache hit that fills the Icache to generate bad
			Icache fill parity
Reserved	[25:0]	—	—

5.2.13 Exception Summary Register – EXC_SUM

The exception summary register (EXC_SUM) is a read-only register that contains information about instructions that have triggered traps. The register is updated at trap delivery time. Its contents are valid only if it is read (by way of a HW_MFPR) in the first fetch block of the exception handler. There are three types of traps for which this register captures related information:

•Arithmetic traps: The instruction generated an exceptional condition that should be reported to the operating system, and/or the FPCR status bit associated with this condition is clear and should be set by PALcode. Additionally, the REG field con- tains the register number of the destination specifier for the instruction that trig- gered the trap.

•Istream ACV: The BAD_IVA bit of this register indicates whether the offending Istream virtual address is latched into the EXC_ADDR register or the VA register.

•Dstream exceptions: The REG field contains the register number of either the source specifier (for stores) or the destination specifier (for loads) of the instruction that triggered the trap.

Figure 5–20shows the exception summary register.

21264/EV68A Hardware Reference Manual Internal Processor Registers 5–13