Required Palcode Function Codes; Opcodes Reserved For Palcode; Hw_Ld Instruction - Compaq EV68A Hardware Reference Manual

When executing in PALmode, there are certain restrictions for using the privileged
instructions because PALmode gives the programmer complete access to many of the
internal details of the 21264/EV68A. Refer to Section 6.4 for information on these spe-
cial PALmode instructions.
Caution:

6.3 Required PALcode Function Codes

Table 6–1 lists opcodes required for all Alpha implementations. The notation used is
oo.ffff, where oo is the hexadecimal 6-bit opcode and ffff is the hexadecimal 26-bit
function code.
Table 6–1 Required PALcode Function Codes
Mnemonic
DRAINA
HALT
IMB

6.4 Opcodes Reserved for PALcode

Table 6–2 lists the opcodes reserved by the Alpha architecture for implementation-spe-
cific use. These opcodes are privileged and are only available in PALmode.
Table 6–2 Opcodes Reserved for PALcode
Mnemonic
HW_LD
HW_ST
HW_RET
HW_MFPR
HW_MTPR
These instructions generally produce an OPCDEC exception if executed while the pro-
cessor is not in PALmode. If I_CTL[HWE] is set, these instructions can also be exe-
cuted in kernel mode. Software that uses these instructions must adhere to the PALcode
restrictions listed in this section.

6.4.1 HW_LD Instruction

PALcode uses the HW_LD instruction to access memory outside the realm of normal
Alpha memory management and to perform special Dstream load transactions. Data
alignment traps are disabled for the HW_LD instruction.
Figure 6–1 shows the HW_LD instruction format.
21264/EV68A Hardware Reference Manual
It is possible to cause unintended side effects by writing what appears to be
perfectly acceptable PALcode. As such, PALcode is not something that
many users will want to change. Before writing PALcode, at least become
familiar with the information in Appendix D.
Type
Privileged
Privileged
Unprivileged
Architecture
Opcode Mnemonic
1B PAL1B
1F PAL1F
1E PAL1E
19 PAL19
1D PAL1D
Required PALcode Function Codes
Function Code
00.0002
00.0000
00.0086
Function
Dstream load instruction
Dstream store instruction
Return from PALcode routine
Copies the value of an IPR into an integer GPR
Writes the value of an integer GPR into an IPR
Privileged Architecture Library Code
6–3