Vax 613 0S Instruction Manual Page 306

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IF a system machine check abort is pending (IRQ4) THEN
check for interrupt bits set in the TC interrupt register
IF one of the bits is set THEN
Save the cause of the error
Go build the machine check log
vector to 660
ELSE
dismiss the interrupt
17.5 INTERRUPT PALcode
The INTERRUPT PALcode will be dispatched to when any correctable,
uncorrectable, or I/O interrupt occurs in the DEC 3000 AXP. The PALcode
performs the following operations:
Determines the cause of the interrupts by reading the HIRR register
Builds the interrupt stack frame and places it on the kernel stack
Determines which SCB vector must be dispatched to and places the vector
address in R2 and the vector parameter in R3
Causes data pertaining to the interrupt to be written to R4 and R5
Exits the PALcode and enters the interrupt handling routine, whose address
is located in R2
The algorithm of the INTERRUPT PALcode is:
IF HALT interrupt (IRQ5) is set THEN
Enter the console
IF system machine abort (IRQ4) is set THEN
check for cause of interrupt
IF one is really there THEN
build log and vector to 660 off of SCB
IF I/O interrupt (IRQ3) is set THEN
Vector to 800 off of SCB (User’s I/O interrupt handler)
IF interval timer interrupt (IRQ1) THEN
Read TOY/NVR CSRC to clear the pending interrupt
Update the absolute time
Vector to 600 off the SCB (user’s interval timer handler)
IF correctable I/O interrupt is set (IRQ2) THEN
Build machine check log
Vector to 620 off of the SCB
17–6 DEC 3000 AXP PALcode
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