The IP register is a device that keeps track of the address of an instruction to be executed next. This device is referred to as an instruction pointer. When an instruction is issued to a microprocessor, it is stored in the instruction pointer register. When this instruction is executed, the value of the instruction pointer register is placed on the address bus, which then sends it to the memory unit. After the memory unit returns the instruction at the address, it latches it into the instruction register. Then, the value of the instruction pointer register is incremented and overwritten. Then, the cycle begins again.
When a macro instruction retires, its IP pointer is updated to point to the following macro instruction. The retiring microinstruction must be the last in the microcode flow and carry an EOM marker. By doing this, the processor will ensure that it has followed the correct instruction path and hasn’t fetched any erroneous instructions. This means that the IP pointer is reset. It is a crucial bit in the execution of instructions.
The IP- delta is calculated when the processor fetches the instruction. It can either be added to the current instruction pointer in the instruction decoder 106 or transferred to the branch information table in BTB 104. This branch information table stores fall through instruction pointers of branch instructions—the PDST of the branch instruction indexes this table. If a microcode sequence isn’t available for fetching the instruction, the IP- delta still represents the faulting macro instruction.
The IP- M flag is a special instruction in microcode that is inserted into the instruction stream. This instruction specifies the type of fault that has occurred. In the Intel microprocessor architecture, this is the default mode for handling these problems. It also enables the processor to be configured to recognize page faults, a common error condition in computer code. And because the UIP flag is unique, the UIP can be updated as often as once every ten minutes.
In addition to the IP flag, there are other registers in a microprocessor that have similar functions. The CS register contains the address of a 64-KB segment that has instructions for that processor. All accesses to this segment are handled through this code segment. This register is not directly changed, but it is updated automatically during a far call, jump, and return instructions. Lastly, the Stack Pointer (SP) register provides an offset value within the stack of a program.
