Motorola MVME1X7P manual 101

GCSR Programming Model

The Location Monitor Status register provides the status of the location monitors. A location monitor bit is cleared when the VMEchip2 detects a VMEbus cycle to the corresponding location monitor address. When the LM0 or LM1 bits are cleared, an interrupt is set to the local bus interrupter. If the LM0 or LM1 interrupt is enabled in the local bus interrupter, then a local bus interrupt is generated. The location monitor bits are set by writing a 1 to the corresponding bit in the location monitor register. LM0 and LM1 can also be set by writing a 1 to the corresponding clear bits in the local interrupt clear register.

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Caution

The Interrupt Control register provides four bits that allow the VMEbus to interrupt the local bus. An interrupt is sent to the local bus interrupter when one of the bits is set. If the interrupt is enabled in the local bus interrupter, then a local bus interrupt is generated. The interrupt bits are cleared by writing a 1 to the corresponding bit in the interrupt clear register.

The Board Control register allows a VMEbus master to reset the local bus, prevent the VMEchip2 from driving the SYSFAIL signal line, and detect if the VMEchip2 wants to drive the SYSFAIL signal line.

The six General Purpose registers can be read and written from both the local bus and the VMEbus. These registers are provided to allow local bus masters to communicate with VMEbus masters. The function of these registers is not defined by this specification. The GCSR supports read-modify-write cycles such as TAS.

The GCSR allows a VMEbus master to reset the local bus. This feature is very dangerous and should be used with caution.

The local reset feature is a partial system reset, not a complete system reset such as powerup reset or SYSRESET. When the local bus reset signal is asserted, a local bus cycle may be aborted. The VMEchip2 is connected to both the local bus and the VMEbus and if the aborted cycle is bound for the VMEbus, erratic operation may result.

Communications between the local processor and a VMEbus master should use interrupts or mailbox locations; reset should not be used in normal communications. Reset should be used only when the local processor is halted or the local bus is hung and reset is the last resort.

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