2.1.2.10 Memory Read Multiple Command

This command is identical to the Memory Read command except that it additionally indicates that the master may intend to fetch more than one cache line before disconnecting. The LSI53C875A supports PCI Memory Read Multiple functionality and issues Memory Read Multiple commands on the PCI bus when the Read Multiple Mode is enabled. This mode is enabled by setting bit 2 (ERMP) of the DMA Mode (DMODE) register. If cache mode is enabled, a Memory Read Multiple command is issued on all read cycles, except opcode fetches, when the following conditions are met:

The CLSE bit (Cache Line Size Enable, bit 7, DMA Control (DCNTL) register) and the ERMP bit (Enable Read Multiple, bit 2, DMA Mode (DMODE) register) are set.

The Cache Line Size register for each function contains a legal burst size value (2, 4, 8, 16, 32, or 64) and that value is less than or equal to the DMODE burst size.

The transfer will cross a cache line boundary.

When these conditions are met, the chip issues a Memory Read Multiple command instead of a Memory Read during all PCI read cycles.

Burst Size Selection – The Read Multiple command reads in multiple cache lines of data in a single bus ownership. The number of cache lines to read is a multiple of the cache line size specified in Revision 2.2 of the PCI specification. The logic selects the largest multiple of the cache line size based on the amount of data to transfer, with the maximum allowable burst size determined from the DMA Mode (DMODE) burst size bits, and the Chip Test Five (CTEST5), bit 2.

2.1.2.11 Dual Address Cycle (DAC) Command

The LSI53C875A performs DACs when 64-bit addressing is required. Refer to the PCI 2.2 specification. If any of the selector registers contain a nonzero value, a DAC is generated. See 64-bit SCRIPTS Selectors in Chapter 4, “Registers,”for additional information.

2.1.2.12 Memory Read Line Command

This command is identical to the Memory Read command, except that it additionally indicates that the master intends to fetch a complete cache

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Functional Description

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LSI 53C875A technical manual Memory Read Multiple Command, Dual Address Cycle DAC Command, Memory Read Line Command