Programmable priority branch circuit

Details Programmable priority branch circuit Programmable priority branch circuit

1988-10-07

1990-11-20

Eng, David Y.

Boots, shoes, and leggings

3642414, 3642428, G06F 942, G06F 1326

Patent

active

049723421

ABSTRACT:
A special purpose circuit unit, responsive to a special BBD instruction, provides for more efficient execution of program branches required in poll and test type routines used by data processors. This unit can easily be added to almost any contemporary processing system to speed up performance of priority branch operations. It includes: a stack of registers loadable with branch addresses designating locations of branch target instructions, an input register for holding bits representing branch conditions accessible from immediate (programmable) storage, and a programmable priority encoder responsive to the BBD instruction to select an address from the stack in accordance with the position in the input register of a highest priority one of the bits representing an active request for instruction branching. The selected address is used to fetch an instruction representing the start of a program segment for attending to the selected branch condition. Contents of the branch address stack are alterable by program to allow for varying selections of branch routines to fulfill conditions denotable by different sets of bits loadable into the input register. The priority encoder includes a stack of selection control registers which are also loadable by programs, to allow for variability in the priority ordering accorded to the bit positions of the input register. By dynamically loading information into the branch address and priority selection stacks, subject BBD unit can be shared dynamically for resolving sequence branching relative to multiple different classes of conditions or events depending on system requirements. The unit is configurable to execute its priority and branch address selection operations together in a single clock cycle of the system. In pipelined systems, the BBD function can be conveniently accommodated in parallel with other system functions.

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