Software Support Considerations

VMEbus Access Time-out

A VMEbus Access Time-out occurs whenever a VMEbus bound transfer does not receive a VMEbus bus grant within the programmed time. This is usually caused by another bus master holding the bus for an excessive period of time.

VMEbus BERR*

A VMEbus BERR* occurs when the BERR* signal line is asserted on the VMEbus while a local bus master is accessing the VMEbus. VMEbus BERR* should occur only if: an initialization routine samples to see if a device is present on the VMEbus and it is not, software accesses a nonexistent device within the VMEbus range, incorrect configuration information causes the VMEchip2 to incorrectly access a device on the VMEbus (such as driving LWORD* low to a 16-bit board), a hardware error occurs on the VMEbus, or a VMEbus slave reports an access error (such as parity error).

Local DRAM Parity Error

Note The 400/500-Series MVME172 models do not contain parity DRAM.

When parity checking is enabled, the current bus master receives a bus error if it is accessing the local DRAM and a parity error occurs.

VMEchip2

An 8- or 16-bit write to the LCSR in the VMEchip2 causes a local BERR*.

Bus Error Processing

Because different conditions can cause bus error exceptions, the software must be able to distinguish the source. To aid in this, status registers are provided for every local bus master. The next section describes the various causes of bus error and the associated status registers.

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Motorola MVME172 manual VMEbus Access Time-out, VMEbus Berr, Local Dram Parity Error, VMEchip2, Bus Error Processing