![](http://datasheet.mmic.net.cn/390000/SYM53C1010-33_datasheet_16836324/SYM53C1010-33_49.png)
SCSI Functional Description
2-21
information from the internal RAM, these fetches remain internal to the
chip and do not use the PCI bus. In addition, any SCRIPTS instruction
that contains a source or destination address residing in SCRIPTS RAM
memory space remains internal to the chip and does not generate PCI
cycles. SCRIPTS instructions able to access SCRIPTS RAM memory
space in this manner include Memory-to-Memory moves, Load/Stores,
and Block Moves. While an internal cycle is occurring, any external PCI
slave cycle is retried on the PCI bus. Setting the DISRC (Disable Internal
SCRIPTS RAM Cycles) bit in the
Chip Control Zero (CCNTL0)
register
disables this feature.
SCRIPTS RAM should be initialized before it is read. Reading SCRIPTS
RAM before initialization will result in the SCRIPTS RAM parity bit, bit 7,
being set in the
Shadowed SCSI SGE Status 0
register.
PCI system BIOS can relocate the RAM anywhere in the 64-bit address
space.
Base Address Register Three (BAR3) (SCRIPTS RAM)
and
Base
Address Register Four (BAR4) (SCRIPTS RAM)
, in the PCI configuration
space, contain the base address of the internal RAM. To simplify
SCRIPTS instruction loading, the base address of the RAM appears in
the
Scratch Register B (SCRATCHB)
register when bit 3 of the
Chip Test
Two (CTEST2)
register is set. The upper 32 bits of a 64-bit base address
are in the
SCRIPT Fetch Selector (SFS)
register. The RAM is byte
accessible from the PCI bus and is visible to any bus mastering device
on the bus. External, CPU accesses to the RAM follow the same timing
sequence as a standard slave register access, except that the required
target wait-states drop from 5 to 3. SCRIPTS RAM must first be written
before being read in order to initialize SCRIPTS RAM parity. If a
SCRIPTS RAM parity error is encountered a SCSI Gross Error interrupt
will be signaled.
A complete set of development tools is available for writing custom
drivers with SCSI SCRIPTS. For more information on the SCSI SCRIPTS
instructions supported by the SYM53C1010, see
Chapter 5, “SCSI
SCRIPTS Instruction Set”
.
2.2.3 64-Bit Addressing in SCRIPTS
The PCI interface for the SYM53C1010 provides 64-bit address and data
capability in the initiator mode. The chip can also respond to 64-bit
addressing in the target mode.