Specifications

Power Hawk 620/640 Hardware Environmen

7-13

whereby the IACK* signal is propagated to each device via an IACKIN/IACKOUT*

signal chain through the slots on the I/O bus, the interrupt request acknowledgment signal

IACK* is received first by the interrupt requester in the lowest slot number. The falling

edge of the active low on the IACK* signal validates the data on A03 to A01 address lines.

Upon detecting its interrupt level code on line A01-A03 on the falling edge of IACK* low,

the interrupt requester identifies itself by placing an implementation-dependent 8- or 16-

bit code on the data lines. This code is called STATUS/ID information in the VMEbus

standard. This implementation of the VMEbus standard uses the 8-bit version of the

STATUS/ID information. When the interrupt handler on the (H)VME bus forwards an

interrupt acknowledge to a processor, the low-level portion of the operating system

interrupt subsystem reads the code to index one of 256 addresses of interrupt-handling

routines. This code is an interrupt vector.

The interrupt vector can be conﬁgured through a register programmed via slave or master

programming, jumpers or switches, or with programmed assembly hardware. The register,

jumpers, switches, or assembly hardware are on the VME device itself.

If the vector byte is programmed, then the interrupt vector can be dynamically allocated

from the kernel interrupt vector table and then assigned to the device during bootstrap via

programmed I/O. Otherwise, if the interrupt vector is hard-wired (preset) in hardware,

then the interrupt vector must be conﬁgured by appropriate calls to ivec-init() from a

driver during system initialization. Information needed to dynamically allocate interrupt

vectors or modify the kernel interrupt vector table is provided in Chapter 10.

PCI Address Decode 7

PCI address decode registers in the Tundra Universe VME Bridge provide mappings on

64KB boundaries to the various VME address spaces and PCI memory. The default map-

ping is shown in the following Table 7-3. The address space assigned to VME A32 space

can be modified with the config(1m) routine, resulting in modification to the PCI

memory space.