我是本科生，第一次上这个论坛，高手们一定要帮帮我啊：）
老师给我一些sparc的资料。用现成的IU扩展出个最小系统。
资料封皮：Data Sheet for the SPARC811 Chip
其中有一些memory subsystem interface signals:
A[31:0] ASI[7:0] D[31:0]......
WRT(output write tag)
I_NULL(output Null Cycle)
尤其是这个i_null总是在store指令的后几个流水cycle被置位。书上还说：
This signal indicates the current memory access is nullified by the processr.I_Null is used to disable cache miss and memory exception for the current memory access.
Under some conditions, the processor is unable to fetch an instruction, usually because a prior multicycle instruction needs to use the bus.When this occurs, the processor asserts I_null to indicate that the current fetch cycle should be nullified.
有人熟悉这个吗？I_null信号到底是干什么的？谢谢。
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