MIPS R10000 Microprocessor User's Manual - SGI TechPubs Library

System Interface Operations 127
External Response Protocol
External Block Data Response Protocol
The processor supports two classes of external responses:
• external data responses provide a double/single/partial-word of data
or provide a block of data using the SysAD[63:0] bus
• external completion responses provide an acknowledge, error, or
negative acknowledge indication using the SysResp[4:0] bus
An external agent may only issue an external data response to the processor when
the System interface is in slave state. If the System interface is not already in slave
state, the external agent must first negate SysGnt* and then wait for the processor
to assert SysRel*. If the System interface is already in slave state, the external
agent may issue an external data response immediately.
External data responses may be accepted by the processor in adjacent SysClk
cycles and in arbitrary order, relative to corresponding processor requests.
An external agent may issue an external completion response when the System
interface is in either master or slave state. External completion responses may be
accepted by the processor in adjacent SysClk cycles and in arbitrary order,
relative to the corresponding processor requests.
An external agent may issue an external block data response in response to a
processor block read or upgrade request.
An external agent issues an external block data response with 8 or 16 data cycles.
Each data cycle consists of the following:
• asserting SysCmd[11]
• driving the request number associated with the corresponding
processor request on SysCmd[10:8]
• driving the data quality indication on SysCmd[5]
• driving the data type indication on SysCmd[4:3]
• driving the cache block state on SysCmd[2:1]
• driving the ECC check indication on SysCmd[0]
• driving the data on SysAD[63:0]
• asserting SysVal*
The first 7 or 15 data cycles have a response data type indication, and the last data
cycle has a response last data type indication. The external agent may negate
SysVal* between data cycles of an external block data response.
MIPS R10000 Microprocessor User's Manual Version 2.0 of January 29, 1997