D PALcode Instruction Summaries

This appendix summarizes the Privileged Architecture Library (PALcode) instructions that are required to support an Alpha AXP system.

By including the file pal.h (use #include <alpha/pal.h>) in your assembly language program, you can use the symbolic names for the PALcode instructions.

D.1 Unprivileged PALcode Instructions

Table D-1 describes the unprivileged PALcode instructions.

Table D-1: Unprivileged PALcode Instructions

Symbolic Name	Number	Operation and Description
`PAL_bpt`	0x80	Break Point Trap - switches mode to kernel mode, builds a stack frame on the kernel stack, and dispatches to the breakpoint code.
`PAL_bugchk`	0x81	Bugcheck - switches mode to kernel mode, builds a stack frame on the kernel stack, and dispatches to the breakpoint code.
`PAL_callsys`	0x83	System call - switches mode to kernel mode, builds a callsys stack frame, and dispatches to the system call code.
`PAL_gentrap`	0xaa	Generate Trap - switches mode to kernel, builds a stack frame on the kernel stack, and dispatches to the gentrap code.
`PAL_imb`	0x86	I-Stream Memory Barrier - makes the I-cache coherent with main memory.
`PAL_rduniq`	0x9e	Read Unique - returns the contents of the process unique register.
`PAL_wruniq`	0x9f	Write Unique - writes the process unique register.

D.2 Privileged PALcode Instructions

The privileged PALcode instructions can be called only from kernel mode. They provide an interface to control the privileged state of the machine.

Table D-2 describes the privileged PALcode instructions.

Table D-2: Privileged PALcode Instructions

Symbolic Name	Number	Operation and Description
`PAL_halt`	0x00	Halt Processor - stops normal instruction processing. Depending on the halt action setting, the processor can either enter console mode or the restart sequence.
`PAL_rdps`	0x36	Read Process Status - return the current process status.
`PAL_rdusp`	0x3a	Read User Stack Pointer - reads the user stack pointer while in kernel mode and returns it.
`PAL_rdval`	0x32	Read System Value - reads a 64-bit per-processor value and returns it.
`PAL_rtsys`	0x3d	Return from System Call - pops the return address, the user stack pointer, and the user global pointer from the kernel stack. It then saves the kernel stack pointer, sets mode to user mode, enables interrupts, and jumps to the address popped off the stack.
`PAL_rti`	0x3f	Return from Trap, Fault, or Interrupt - pops certain registers from the kernel stack. If the new mode is user mode, the kernel stack is saved and the user stack is restored.
`PAL_swpctx`	0x30	Swap Privileged Context - saves the current process data in the current process control block (PCB). Then it switches to the PCB and loads the new process context.
`PAL_swpipl`	0x35	Swap IPL - returns the current IPL value and sets the IPL.
`PAL_tbi`	0x33	TB Invalidate - removes entries from the instruction and data translation buffers when the mapping entries change.
`PAL_whami`	0x3c	Who Am I - returns the process number for the current processor. The processor number is in the range 0 to the number of processors minus one (0..numproc-1) that can be configured into the system.
`PAL_wrfen`	0x2b	Write Floating-Point Enable - writes a bit to the floating-point enable register.
`PAL_wrkgp`	0x37	Write Kernel Global Pointer - writes the kernel global pointer internal register.
`PAL_wrusp`	0x38	Write User Stack Pointer - writes a value to the user stack pointer while in kernel mode.
`PAL_wrval`	0x31	Write System Value - writes a 64-bit per-processor value.
`PAL_wrvptptr`	0x2d	Write Virtual Page Table Pointer - writes a pointer to the virtual page table pointer (vptptr).