that could be used for other system tasks. The preferred method of detecting interrupts in most systems is hardware interrupts. In this case, the LSI53C810A asserts the Interrupt Request (IRQ/) line that interrupts the microprocessor, causing the microprocessor to execute an interrupt service routine. A hybrid approach would use hardware interrupts for long waits, and use polling for short waits.

2.7.1.1 Registers

The registers in the LSI53C810A that are used for detecting or defining interrupts are the Interrupt Status (ISTAT), SCSI Interrupt Status Zero (SIST0), SCSI Interrupt Status One (SIST1), DMA Status (DSTAT), SCSI Interrupt Enable Zero (SIEN0), SCSI Interrupt Enable One (SIEN1), DMA Control (DCNTL), and DMA Interrupt Enable (DIEN).

ISTAT The ISTAT is the only register that can be accessed as a slave during SCRIPTS operation. Therefore, it is the register that is polled when polled interrupts are used. It is also the first register that should be read after the IRQ/ pin is asserted in association with a hardware interrupt. The INTF (Interrupt-on-the-Fly) bit should be the first interrupt serviced. It must be written to one to be cleared. This interrupt must be cleared before servicing any other interrupts.

If the SIP bit in the Interrupt Status (ISTAT) register is set, then a SCSI-type interrupt has occurred and the SCSI Interrupt Status Zero (SIST0) and SCSI Interrupt Status One (SIST1) registers should be read.

If the DIP bit in the Interrupt Status (ISTAT) register is set, then a DMA-type interrupt has occurred and the DMA Status (DSTAT) register should be read.

SCSI-type and DMA-type interrupts may occur simultaneously, so in some cases both SIP and DIP may be set.

SIST0 and SIST1 TheSCSI Interrupt Status Zero (SIST0) and SCSI Interrupt Status One (SIST1) registers contain the SCSI-type interrupt bits. Reading these registers determines which condition or conditions caused the SCSI-type interrupt, and clears that SCSI interrupt condition.

If the LSI53C810A is receiving data from the SCSI bus and a fatal interrupt condition occurs, the LSI53C810A attempts to send the contents of the DMA FIFO to memory before generating the interrupt.

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Functional Description

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LSI 53C810A technical manual Registers