LSI Logic Confidential
15-20
Serial I/O Port
Copyright © 2001, 2002 by LSI Logic Corporation. All rights reserved.
The SIO Reset register allows users to “software reset” each of the
peripheral modules.
15.5.1 Interrupt Hierarchy
The SIO module presents a single signal to the SPARC processor to
indicate that an interrupt is pending and needs to be serviced. This signal
is generated by OR-ing the register bits of both the SIO Top Level
Module Interrupt Status Register (SIO_IRQ_STATUS) and the SIO Top
Level DMA Interrupt Status Register (SIO_DMA_IRQ).
The SIO Top Level Module Interrupt Status Register (SIO_IRQ_STATUS)
stores the state of each peripheral module’s interrupt output pins. When
servicing an interrupt, the appropriate module’s register must be serviced
before clearing SIO_IRQ_STATUS. Otherwise, if the module generates a
level interrupt (interrupt output pin stays high until serviced) and
SIO_IRQ_STATUS is cleared, on the following cycle, the appropriate bit
in SIO_IRQ_STATUS is set again. This indicates that a new interrupt is
now pending when it really is not.
The SIO Top Level DMA Interrupt Status Register (SIO_DMA_IRQ)
stores the bits of the SIO DMA Engine Interrupt Status Register
(INTR_STATUS_ADDR). It is this register, INTR_STATUS_ADDR, which
actually stores the interrupt output pins of all of the various SIO DMA
channels. In contrast to SIO_IRQ_STATUS, SIO_DMA_IRQ is two levels
away from each of the DMA channel’s interrupt output pins. When
servicing an interrupt, INTR_STATUS_ADDR must be cleared before
clearing SIO_DMA_IRQ. Otherwise, on the following cycle, the
appropriate bit in SIO_DMA_IRQ is still set. This indicates that a new
interrupt is now pending when it really is not.
By writing the Module Interrupt Enable/DMA Interrupt Mask registers, the
user can control which interrupts are latched in the Module Interrupt
Status/DMA Interrupt Status registers, respectively. The register bits of
the Module Interrupt Status register and the DMA Interrupt Status
register are OR’d together to signal to the SPARC processor that the SIO
has an interrupt pending.
Содержание DMN-8600
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