Software Support Considerations

VMEbus Accesses to the Local Bus

The VMEchip2 includes a user-programmable map decoder for the VMEbus to local bus interface. The map decoder allows you to program the starting and ending address and the modifiers the MVME172 responds to.

VMEbus Short I/O Memory Map

The VMEchip2 includes a user-programmable map decoder for the GCSR. The GCSR map decoder allows you to program the starting address of the GCSR in the VMEbus short I/O space.

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Software Support Considerations

The MVME172 is a complex board that interfaces to the VMEbus and SCSI bus. These multiple bus interfaces raise the issue of cache coherency and support of indivisible cycles. There are also many sources of bus error. First, let us consider how interrupts are handled.

Interrupts

The MC68060 uses hardware-vectored interrupts.

Most interrupt sources are level and base vector programmable. Interrupt vectors from the MC2 chip and the VMEchip2 have two sections, a base value which can be set by the processor, usually the upper four bits, and the lower bits which are set according to the particular interrupt source. There is an onboard daisy chain of interrupt sources, with interrupts from the MC2 chip having the highest priority, those from the IP2 chip having the next highest priority, and interrupt sources from the VMEchip2 having the lowest priority. Refer to Appendix A for an example of interrupt usage.

The MC2 chip, IP2 chip, and VMEchip2 ASICs are used to implement the multilevel MC680x0 interrupt architecture. A PLD is used to combine the individual IPLx signals from each ASIC.

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Motorola MVME172 manual Software Support Considerations, Interrupts, VMEbus Accesses to the Local Bus