MIPS R10000 Microprocessor User's Manual - SGI TechPubs Library

System Interface Operations 133
External Intervention Request Protocol
Cycle
SysClk
Master
SysReq*
SysGnt*
SysRel*
SysCmd(11:0)
SysCmdPar
SysAD(63:0)
SysADChk(7:0)
SysVal*
SysRdRdy*
SysWrRdy*
SysState(2:0)
SysStatePar
SysStateVal*
SysResp(4:0)
SysRespPar
SysRespVal*
An external agent issues an external intervention request to obtain a Shared or
Exclusive copy of a secondary cache block.
An external agent issues an external intervention request with a single address
cycle; this address cycle consists of the following:
• negating SysCmd[11]
• driving a request number on SysCmd[10:8]
• driving the intervention command on SysCmd[7:5]
• driving the ECC check indication on SysCmd[0]
• driving the target indication on SysAD[63:60]
• driving the physical address on SysAD[39:0]
• asserting SysVal*
An external agent may only issue an external intervention request address cycle
when the System interface is in slave state; typically a free request number is
specified. An external agent may have as many as eight external intervention
requests outstanding on the System interface at any given time.
Figure 6-20 depicts three external intervention requests. Since the System
interface is initially in master state, the external agent must first negate SysGnt*
and then wait until the processor relinquishes mastership of the System interface
by asserting SysRel*.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
P0 P0 P0 P0 P0 - EA EA EA EA EA EA EA EA EA EA EA
Figure 6-20 External Intervention Request Protocol
MIPS R10000 Microprocessor User's Manual Version 2.0 of January 29, 1997
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