4-66
Registers
met), on writes to the
, on
regular MMOV instructions, and when an interrupt is
generated. Based on the burst length as determined by
the values in the
register, the unit
automatically determines the maximum burst size that it
is capable of performing. If the burst threshold is set to
8 Dwords, the prefetch unit fetches instructions in two
bursts of 4 Dwords. If the burst threshold is set to
16 Dwords, or greater, the prefetch unit fetches
instructions in one burst of 8 Dwords. Burst thresholds of
less than 8 Dwords cause the prefetch unit to be
disabled. PCI Cache commands (Read Line and Read
Multiple) are issued if PCI caching is enabled.
Prefetching from SCRIPTS RAM is not supported and is
unnecessary due to the speed of the fetches. When
fetching from SCRIPTS RAM, the setting of this bit has
no effect on the fetch mechanism from SCRIPTS RAM.
The prefetch unit does not support 64-bit data instruction
fetches across the PCI bus. Prefetches of SCRIPTS
instructions are 32-bits in width.
SSM
Single-Step Mode
4
Setting this bit causes the LSI53C1000 to stop after
executing each SCRIPTS instruction and to generate a
single step interrupt. When this bit is cleared the
LSI53C1000 does not stop after each instruction. It
continues fetching and executing instructions until an
interrupt condition occurs. For normal SCSI SCRIPTS
operation, keep this bit cleared. To restart the
LSI53C1000 after it generates a SCRIPTS Step interrupt,
read the
Interrupt Status Zero (ISTAT0)
and
registers to recognize and clear the interrupt.
Then set the START DMA bit in this register.
IRQM
IRQ Mode
3
When set, this bit enables a totem pole driver for the
INTA/ pin. When cleared, this bit enables an open drain
driver for the INTA/ pin with an internal weak pull-up. The
bit should remain cleared to retain full PCI compliance.
Содержание LSI53C1000
Страница 6: ...vi Preface...
Страница 16: ...xvi Contents...
Страница 28: ...1 12 Introduction...
Страница 234: ...4 124 Registers...
Страница 314: ...6 40 Specifications This page intentionally left blank...
Страница 318: ...6 44 Specifications This page intentionally left blank...
Страница 344: ...6 70 Specifications This page intentionally left blank...
Страница 350: ...6 76 Specifications Figure 6 42 LSI53C1000 329 Ball Grid Array Bottom view...
Страница 352: ...6 78 Specifications...
Страница 360: ...A 8 Register Summary...
Страница 376: ...IX 12 Index...