Compaq 21264 - Manual (Page 197)

Alpha 21264/EV67 Hardware Reference Manual Privileged Architecture Library Code 6–13
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 40
16
to 7F
16
inclusive
• Is greater than BF
16
• Is between 00
16
and 3F
16
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)
6.8.2 PALcode 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 6–8 shows the PALcode exception entry locations and their offset from the
PAL_BASE IPR.
Table 6–8 PALcode Exception Entry Locations
Entry Name Type Offset
16
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
, 1B
16
, 1D
16
, 1E
16
or 1F
16
, not PALmode or
not I_CTL[HWE]
• Extended precision IEEE format
• Unimplemented function field of opcodes 14
16
or 1C
16
IACV Fault 480 Istream access violation or virtual address sign check error.