What are register banks?

What are register banks?

A register bank is used for the programmable registers used by assembly language programmers. It can be viewed as the hardware equivalent of a software array. It has ports for reading and writing data given an index. A register number is used as the index in a register bank. …

What is the main use of banked register?

A banked register maps one-to-one onto a user mode register. If you change processor mode, a banked register from the new mode will replace an existing register. For example, when the processor is in the interrupt request mode, the instructions you execute still access registers named r13 and r14.

What are the banked register in FIQ mode of ARM?

Seven FIQ mode registers for banked R8-R12, SP and LR. Two Monitor mode registers for banked SP and LR. These are only present if the Security Extensions are implemented. Two Hyp mode registers for banked SP, and to hold the return address from Hyp mode.

What is the function of link register?

A link register is a special-purpose register which holds the address to return to when a function call completes. This is more efficient than the more traditional scheme of storing return addresses on a call stack, sometimes called a machine stack.

What is R12 register?

The choice of R12 allows some systems to use R9-R11 as callee-saved general purpose registers without disrupting any sequence of similar registers. From the APCS, The ip register has a dedicated role only during function call; at other times it may be used as a scratch register.

What is the function of of register r15 in arm7tdmi?

Registers r14 and r15 have special functions as the subroutine link register and the program counter. Register 14 is used as the subroutine Link Register (LR). R14 receives a copy of r15 when a Branch with Link (BL) instruction is executed.

What is R14 register?

R14, link register (LR) R14 is also called the Link Register (LR). This is used for holding the return address when calling a function or subroutine. At the end of the function or subroutine, the program control can return to the calling program and resume by loading the value of LR into the Program Counter (PC).

Where does link register point?

Each old lr (link register) is stored in the old fp (frame pointer). The sp and fp are a data aspect of functions. Your point B is the active pc and sp . Point A is actually the fp and lr ; unless you call yet another function and then the compiler might get ready to setup the fp to point to the data in B.

What is register banking and how does it work?

Register banking refers to providing multiple copies of a register at the same address. Taken from section 1.4.6 of the arm docs. The term is referring to a solution for the problem that not all registers can be seen at once. There is a different register bank for each processor mode.

What is ARM register banking and how does it work?

The ISCA paper you linked refers to a different meaning of banking–that kind of banking is used to reduce access port count and is often called pseudo-porting when used for caches. The ARM register banking is meant to simplify and speed exception handling.

What is the difference between a banked register and a processor?

The processor just keeps a safe copy of that set; and will restore the original set on exception return. Banked registers are registers which are not needed and accessible by the current execution mode. When the execution mode changes, the registers needed for the new mode will become usable.

How many registers are there in an ARMv7 processor?

ARM processors, with the exception of ARMv6-M and ARMv7-M based processors, have a total of 37 registers, with 3 additional registers if the Security Extensions are implemented, and in ARMv7-A only, 3 more if the Virtualization Extensions are implemented. The registers are arranged in partially overlapping banks.