Vax 613 0S Instruction Manual Page 181

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10.6 Assignment of CPU Interrupt Pins
Six interrupt pins are provided on the CPU. These interrupts are decribed in
Table 42.
Table 42 Interrupt Pin Allocation
IRQ Pin Definition
IRQ[0] Unused
IRQ[1] SysAD.IntTmr—interval timer interrupt
IRQ[2] SysAD.CorrIntr—correctable interrupt from I/O adapter
IRQ[3] SysAD.IOIntr— OR of all I/O option interrupt lines
IRQ[4] SysAD.UnCorrIntr—uncorrectable interrupt from I/O adapter
IRQ[5] SysAD.Halt—tied to Halt button on enclosure
All interrupt lines, with the exception of HALT and IntTmr, are asserted
synchronously with respect to the CPU’s SysClk1 output and are driven from
latches that must be cleared in order to remove the interrupt request. Refer to
the DECchip 21064-AA Microprocessor Hardware Reference Manual under HIER
and HIRR.
The effective IPL of the five interrupt lines is software-controlled by programming
the HIER internal CPU register.
Note
It is up to software to ensure that some interrupts do not lock out others.
10.7 Error Handling and Recovery
All errors are dispatched through SCB vectors and are handled by service
routines that the operating system must provide, except errors resulting in a
console halt. A halt transfers control directly to a hardware-prescribed address.
Software-driven recovery or retry is not recommended for errors resulting in
console halt.
Hardware Exceptions and Interrupts 10–15
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