XFC Instruction

Purpose:

To provide customer extensions to the instruction set.

Format:

opcode code.rb

Operation:

{XFC fault};

Condition
Codes:

N <- 0;
Z <- 0;
V <- 0;
C <- 0;

Exceptions:

Opcode reserved to customer
Customer reserved exception

Opcodes:

XFC

Extended Function Call

Description:

This instruction requests services of non-standard microcode or software. If no special microcode is loaded then an exception is generated to a kernel mode software simulator. Typically, the next byte would specify which of the several extended functions are requested. Parameters would be passed either as normal operands, or more likely in fixed registers.

Notes:

1.: MacVAX uses this instruction to provide access to the MacVAX simulator. See MacVAX XFC calls.
2.: The assembler will also recognise SYS instead of XFC.