名词缩写

• ISA - Instruction Set Architecture，指令集架构
• PC - Program Counter, holds the address of the instruction that is currently running
• GPRs - 32 General Purpose Registers
• PSW - Program Status Word
• PCXI - Previous Context Information
• CSA - Context Save Area，CSAs are linked together through a Link Word
• TIN - Trap Identification Number
• SP - Stack Pointer, A[10]
• ISP - Interrupt Stack Pointer Register
• SYSCON - System Control Register
• FCX - Free CSA List Head Pointer register
• PCX - Previous Context List

The PCXI, PSW and PC registers are crucial to the procedure for storing and restoring a task’s context

• A[10] is the Stack Pointer (SP) register
• A[11] is the Return Address (RA) register

The events and instructions which cause a break in program execution are:

• Interrupt or service requests
• Traps
• Function calls

The maximum number of interrupt sources is 255

When a trap is taken, the TIN is placed in data register D[15]

The GPRs are an essential part of a task’s context. When saving or restoring a task’s context to and from memory the context is split into the upper and lower contexts:

• Registers A[2] to A[7] and D[0] to D[7] are part of the lower context.
• Registers A[10] to A[15] and D[8] to D[15] are part of the upper context.