AMD-K6-2E/400AFR AMD [Advanced Micro Devices], AMD-K6-2E/400AFR Datasheet - Page 40

• Manufacturer Part Number: AMD-K6-2E/400AFR
• Manufacturer: AMD [Advanced Micro Devices]

AMD-K6™-2E Processor Data Sheet
Branch Execution
Unit
22
Entry into the subroutine occurs with the execution of a CALL
instruction. At that time, the processor pushes the address of
the next instruction in memory following the CALL instruction
onto the stack (allocated space in memory). When the processor
encounters a RET instruction (within or at the end of the
subroutine), the branch logic pops the address from the stack
and begins fetching from that location. To avoid the latency of
main memory accesses during CALL and RET operations, the
return address stack caches the pushed addresses.
The branch execution unit enables efficient speculative
execution. This unit gives the processor the ability to execute
instructions beyond conditional branches before knowing
whether the branch prediction was correct.
The AMD-K6-2E processor does not permanently update the
x86 registers or memory locations until all speculatively
executed conditional branch instructions are resolved. When a
prediction is incorrect, the processor backs out to the point of
the mispredicted branch instruction and restores all registers.
The AMD-K6-2E processor can support up to seven outstanding
branches.
Preliminary Information
Internal Architecture
22529B/0—January 2000
Chapter 2