PALcode Entry Points

Each CALL_PAL instruction includes a function field that is used to calculate the PC of its associated PALcode entry point. The PALcode OPCDEC exception flow will be invoked if the CALL_PAL function field satisfies any of the following requirements:

Is in the range of 4016 to 7F16 inclusive

Is greater than BF16

Is between 0016 and 3F16 inclusive, and IER_CM[CM] is not equal to the kernel mode value 0

If none of the conditions above are met, the PALcode entry point PC is as follows:

PC[63:15] = PAL_BASE[63:15]

PC[14] = 0

PC[13] = 1

PC[12] = CALL_PAL function field [7]

PC[11:6] = CALL_PAL function field [5:0]

PC[5:1] = 0

PC[0] = 1 (PALmode)

6.8.2PALcode Exception Entry Points

When hardware encounters an exception, Ibox execution jumps to a PALcode entry point at a PC determined by the type of exception. The return PC of the instruction that triggered the exception is placed in the EXC_ADDR register and onto the return predic- tion stack.

Table 6–8shows the PALcode exception entry locations and their offset from the

PAL_BASE IPR.

Table 6–8 PALcode Exception Entry Locations

Entry Name

Type

Offset16

Description

DTBM_DOUBLE_3

Fault

100

Dstream TB miss on virtual page table entry fetch. Use three-

 

 

 

level flow.

DTBM_DOUBLE_4

Fault

180

Dstream TB miss on virtual page table entry fetch. Use four-

 

 

 

level flow.

FEN

Fault

200

Floating point disabled.

UNALIGN

Fault

280

Unaligned Dstream reference.

DTBM_SINGLE

Fault

300

Dstream TB miss.

DFAULT

Fault

380

Dstream fault or virtual address sign check error.

OPCDEC

Fault

400

Illegal opcode or function field:

 

 

 

• Opcode 1, 2, 3, 4, 5, 6 or 7

 

 

 

• Opcode 19 16, 1B16, 1D16, 1E16 or 1F16 , not PALmode or

 

 

 

not I_CTL[HWE]

 

 

 

• Extended precision IEEE format

 

 

 

• Unimplemented function field of opcodes 14 16 or 1C16

IACV

Fault

480

Istream access violation or virtual address sign check error.

21264/EV68A Hardware Reference Manual

Privileged Architecture Library Code 6–13

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Compaq EV68A specifications PALcode Exception Entry Points, PALcode Exception Entry Locations