What's the meaning of Boot and Valid
AbrahamYabo opened this issue · 2 comments
What is the use of Boot and Valid and their meaning in circuit?
Boot在TopTest中已经写好，1表示复位，0表示正常工作，可以用来给PC寄存器做复位信号用；
Valid是CPU的输出，表示当前译码的指令格式正确与否，1表示正确，0表示格式非法（包括暂时不支持执行的指令）。
Generally, Boot is input and Valid is output, which Boot will reset the CPU pc register and start test mode if it is set to 1, and Valid is for some exceptions. Boot should be supported by adding some reset logic while Valid is generated by expectation detection logic. At this stage, single cyclic CPU design, the expection can be considered as expection of instruction fetching and decoding, aka. Unknown instruction happens. In regular instructions, Valid is set to 1. If an unknown instruction is send into Inst of ctlpath, Valid will be set to 0.