# Patent

## Title
Memory mapped register file

## Abstract

A memory mapped register file is disclosed for a data processing system that comprises a memory unit, input ports, and output ports. The memory unit includes a plurality of registers addressable by an encoded address, wherein the encoded address corresponds to a respective one of the plurality of registers and a corresponding processor mode. The input ports receive inputs for addressing at least one register using an encoded address. The output ports output data from at least register addressable by an encoded address.

## Background
RELATED APPLICATIONS
This application claims priority to U.S. Provisional Patent Application No. 60/468,802, entitled “MEMORY MAPPED REGISTER FILE,” filed May 7, 2003, which is expressly incorporated herein by reference. This application is also related to commonly owned U.S. patent application Ser. No. 10/672,774, entitled “DATA PROCESSING SYSTEM WITH REORDER BUFFER AND COMBINED LOAD STORE ARITHMETIC LOGIC UNIT AND PROCESSING METHOD THEREOF,” filed on Sep. 26, 2003, which is expressly incorporated herein by reference.


FIELD
This invention relates generally to data processing systems and, more particularly, to a memory mapped register file for a data processing system.
BACKGROUND
General purpose registers or a “register file” are an essential component of a data processing system's processing architecture. For instance, a microprocessor or central processing unit (CPU) of a data processing system retrieves and stores data from and to one or more general purpose registers to process instructions. These registers allow the data processing system to perform instructions more efficiently. Many prior microprocessor architectures use sixteen general purpose registers designated, e.g., R0 through R15, and operate in different processor modes.
Prior microprocessor architectures that use such general purpose registers also process reduced instruction set computer (RISC) instructions and operate in six different processor modes: user (USR) mode, fast interrupt request (FIQ) mode, interrupt request (IRQ) mode, supervisor (SVC) mode, undefined instruction (UND) mode, and abort exception (ABT) mode. The user mode is typically used for executing user applications. The other modes are “exception handling” modes and halt a user application in the user mode, e.g., responding to an interrupt request. For the exception handling modes, physical access to some of the general purpose registers is performed through multiple memory units of “banked” registers that are mapped to the same general purpose registers, to improve exception handling processing. That is, depending on the exception handling mode, separate and distinct registers are accessed. “Unbanked” general purpose registers do not map to banked registers and are accessed directly in all processor modes.
FIG. 1 illustrates “unbanked” and “banked” general purpose registers for this prior architecture. As shown, general purpose registers 100 includes sixteen registers R0 through R14 and one register that stores a program counter (PC). General purpose registers 100 are divided into unbanked registers 112 and banked registers 111. Unbanked registers 112 correspond to registers R0 through R7 and banked registers 111 correspond to registers R8 through R14. Banked registers 111 map to FIQ banked registers 102, IRQ banked registers 104, SVC banked registers 106, UND banked registers 108, and ABT banked registers 110 for their respective exception handling processor modes. For this prior architecture, general purpose registers R8 through R14 are mapped to multiple memory units, i.e., five separate and distinct banked registers, for different exception handling modes.
For instance, during the interrupt request, supervisor, undefined instruction, or abort exception handling modes, access to general purpose registers R13 through R14 is performed using IRQ, SVC, UND, and ABT banked registers 104, 106, 108, and 110, respectively, instead of registers R13 or R14 of general purpose registers 100. Similarly, during fast interrupt request exception handling mode, access to general purpose registers R8 through R14 is performed using FIQ banked registers 102, instead of registers R8 through R14 of general purpose registers 100. Using these banked registers avoids physical access to the preserved data in general purpose registers 100 corresponding to the respective exception handling modes.
In this manner, for the exception handling modes, physical access to some general purpose registers 100, i.e., R8 through R14 or R13 through R14, is performed using multiple memory units of respective banked registers to improve exception handling. A disadvantage, however, of using banked registers is that it requires a special type of naming scheme to distinguish between the different types of banked registers for the different types of exception handling modes, which increases processing overhead. Furthermore, such a general purpose register or “register file” scheme inefficiently accesses general purpose registers by requiring access to multiple memory units of banked registers for different exception handling modes. In other words, the prior register file requires memory access to five separate and distinct memory units for the five different exception handling modes.
There exists, therefore, a need for an improved scheme for general purpose registers or register files without using multiple banked registers for different processor modes.
SUMMARY
According to one aspect of the invention, a register file for a data processing system comprises a memory unit, input ports, and output ports. The memory unit includes a plurality of registers addressable by an encoded address, wherein the encoded address corresponds to a respective one of the plurality of registers and a corresponding processor mode. The input ports receive inputs for addressing at least one register using an encoded address. The output ports output data from at least register addressable by an encoded address.
According to another aspect of the invention, a register file for a data processing system comprises a memory means, input means, and output means. The memory means includes a plurality of register means addressable by an encoded address, wherein the encoded address corresponds to a respective one of the plurality of register means and a corresponding processor mode. The input means receives inputs for addressing at least one register using an encoded address. The output means outputs data from at least one register addressable by an encoded address.
According to another aspect of the invention, a data processing system comprises a microprocessor that comprises a plurality of pipeline stages including a register file. The register file includes a memory unit, input ports, and output ports. The memory unit includes a plurality of registers addressable by an encoded address, wherein the encoded address corresponds to a respective one of the plurality of registers and a corresponding processor mode. The input ports receive inputs for addressing at least one register using an encoded address. The output ports output data from at least one register addressable by an encoded address.
According to another aspect of the invention, a data processing system comprises a processing means for processing instructions that comprises a pipeline means for executing instructions. The pipeline means comprises register file means that comprises a memory means, an input means, and an output means. The memory means includes a plurality of register means addressable by an encoded address, wherein the encoded address corresponds to a respective one of the plurality of register means and a corresponding processor mode. The input means receives inputs for addressing at least one register means using an encoded address. The output means for outputting output data from at least one register means addressable by an encoded address.
According to another aspect of the invention, a microprocessor comprises an integrated circuit that comprises a memory unit and at least one address encoder. The memory unit includes a plurality of registers addressable by an encoded address, wherein the encoded address corresponds to a respective one of the plurality of registers and a corresponding processor mode. The at least one address encoder provides at least one encoded address for addressing at least one of the registers.
According to another aspect of the invention, a data processing system comprises a memory mapped register file for accessing a plurality of registers using an encoded address, wherein the encoded address corresponds to a respective one of the plurality of registers and a corresponding processor mode.
According to another aspect of the invention, a microprocessor comprises an integrated circuit means that comprises a memory means having a plurality of register means addressable by an encoded address, wherein the encoded address corresponds to a respective one of the plurality of register means and a corresponding processor mode. The memory means also comprises at least one addressing means for providing at least one encoded address for addressing at least one of the register means.
According to another aspect of the invention, an integrated circuit method comprises configuring the integrated circuit to receive processor mode and source data inputs; configuring the integrated circuit to determine an encoded address based on the processor mode and source data inputs, wherein the encoded address corresponds to a respective one of a plurality of registers and a corresponding processor mode; configuring the integrated circuit to address one of the registers using an encoded address; and configuring the integrated circuit to output data from the register addressable by the encoded address.
According to another aspect of the invention, a method for accessing a memory unit having a plurality of registers comprises receiving inputs for accessing the register file; determining at least one encoded address in accordance with the received inputs; accessing the memory unit in accordance with the encoded address, wherein the encoded address corresponds to a respective one of the plurality of registers and a corresponding processor mode; and outputting data from the memory unit accessed with the encoded address.



DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary implementations and embodiments of the invention and, together with the detailed description, serve to explain the principles of the invention. In the drawings,
FIG. 1 illustrates banked and unbanked general purpose registers for a prior art microprocessor architecture;
FIG. 2 illustrates one example of a data processing system having a pipeline microprocessor architecture with a memory mapped register file;
FIG. 3 illustrates in block diagram form one example of inputs and outputs for the memory mapped register file of FIG. 2;
FIG. 4 illustrates a block diagram of one example of general purpose registers for the memory mapped register file 206 of FIG. 3;
FIG. 5 illustrates a diagram of one example of a memory map of general purpose register indexes of FIG. 4 to encoded addresses for the memory mapped register file of FIG. 3;
FIG. 6 illustrates a detailed circuit diagram of one example of the memory mapped register file of FIG. 3;
FIG. 7 illustrates one example of a flow diagram for a method to output source data from the memory mapped register file of FIG. 6; and
FIG. 8 illustrates one example of a flow diagram for a method to write data into the memory mapped register file of FIG. 6.



DETAILED DESCRIPTION
Reference will now be made in detail to exemplary implementations and embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
A memory mapped register file is disclosed that overcomes disadvantages of prior register files and provides a more efficient and simple way of accessing general purpose registers for a data processing system that can operate in multiple processor modes.
According to one example, a register file for a data processing system comprises a memory unit, input ports, and output ports. The memory unit includes a plurality of registers addressable by an encoded address, wherein the encoded address corresponds to a respective one of the plurality of registers and a corresponding processor mode. The input ports receive inputs for addressing at least one register using an encoded address. The output ports output data from at least register addressable by an encoded address.
In this manner, the memory unit can be used to access registers (e.g., general purpose registers) of a register file for different processor modes as opposed to using multiple memory units of “banked registers.” This allows for efficient access to registers, which are accessible in the memory unit. Moreover, processing overhead is improved because each register is addressable by an encoded address without requiring a special naming scheme, as required for a register file that uses multiple memory units of banked registers. Thus, in the following description, reference to a “memory mapped register file” is a register file having a memory unit with a plurality of registers addressable by an encoded addresses. Additionally, the register file described herein can be implemented for various types of microprocessor architectures that require access to registers in different processor modes.
FIG. 2 illustrates one example of a data processing system 200 having a pipeline microprocessor architecture with a memory mapped register file 206. The pipeline can be a RISC pipeline that processes RISC instructions in multiple stages. The techniques described herein, however, can be used for other types of microprocessor instructions. Data processing system 200 includes a pipeline comprising an instruction fetch stage 202, an instruction decode stage 204, a register file 206, an execution stage 208, and a write back or retire logic stage 210. Data processing system 200 also includes a program memory 212 that stores instructions for execution by execution stage 208. In this example, the pipeline stages and memory can be implemented as an integrated circuit (IC) using any combination of circuits, components, memory devices, and bus lines.
Instruction fetch 202 fetches the current instruction from memory (e.g., program memory 212) and forwards the instruction to instruction decode stage 204. Stage 204 decodes the instruction and sends inputs to memory mapped register file 206 to access appropriate registers (e.g., general purpose registers) in order for execution stage 208 to process the instruction. FIG. 3 illustrates in block diagram form one example of inputs and output for memory mapped register file 206. Thus, referring also to FIG. 3, for example, instruction decode stage 204 sends “processor mode inputs” and “source index inputs” to memory mapped register file 206. Memory mapped register file 206 uses the inputs from instruction decode stage 204 to obtain an encoded address for accessing the desired register within memory mapped register file 206 in order to execute the instruction. Thus, data from the accessed register using the encoded address is forwarded to execution stage 208.
Moreover, the “processor mode inputs” and “write index inputs” can be sent to memory mapped register file 206 by other components or control circuitry (not shown) to write data into a desired general purpose register within memory mapped file register 206. For example, data received at “write data inputs” can be written into memory mapped file register 206 at an encoded address derived from the “processor mode inputs” and “write index inputs.” This allows write back or retire logic 210 to send data for storage in memory mapped register file 206 via the “write index inputs”. The manner in which these inputs are used by memory mapped register file 206 is described in further detail below with regards to FIGS. 3 through 6.
Execution stage 208 can include any number of instruction execution units. Examples of execution units include arithmetic logic units (ALUs), load/store units, multiply and accumulate units (MACs), etc. Execution stage 208 also operates with program memory 212 to execute instructions. For example, for a load/store operation, execution stage 208 can store data into program memory 212 after processing an instruction using a load/store execution unit. In one example, instructions are issued to execution stage 208 in-order, but can be executed out-of order in a manner disclosed in the above-noted, commonly owned U.S. patent application, entitled “DATA PROCESSING SYSTEM WITH REORDER BUFFER AND COMBINED LOAD STORE ARITHMETIC LOGIC UNIT AND PROCESSING METHOD THEREOF.”
Thus, in this example, execution stage 208 can forward data from executed instructions (“results data”) to write back or retire logic 210 (“logic 210”). Logic 210 can forward results data back to memory mapped register file 206. For example, logic 210 can write back results of executed instructions from execution stage 208 to memory mapped register file 206. Additionally, for execution stage 208 that can execute instructions out-of-order using a re-order buffer with “retire logic,” as disclosed in the above-noted patent application, logic 210 can retire instructions and send data to memory mapped register file 206. As further explained below, memory mapped register file 206 includes a plurality of write ports to receive write data from logic 210. Accordingly, logic 210 can retire one or more results for instructions at a time that are stored in one or more registers in memory mapped register file 206.
With further reference to FIG. 3, memory mapped register file 206 is scalable to receive any number of inputs and output any number of outputs. Thus, in the example shown in FIG. 3, memory mapped register file 206 includes four sets of input ports to receive processor mode inputs, source index inputs, write index inputs, and write data inputs. Each set of input ports receives a plurality of inputs (input 1 through input N). Memory mapped register file 206 also includes a set of output ports to output source data outputs having output 1 through output N. In this example, memory mapped register file 206 can receive inputs and provide outputs for a multiple issue data processing system. Specifically, memory mapped register file 206 is capable of outputting and writing data for multiple instructions at the same time.
For example, if two instructions require two ALU operations and each operation requires two source data inputs from memory mapped register file 206, memory mapped register file 206 can receive four processor mode inputs and four source index inputs to access and output data from four registers as source data outputs. This capability assumes there are no data dependencies, e.g., the second ALU operation does not require the result of the first ALU operation as an input. In particular, if the first ALU operation is A+B and the second ALU operation is C+D and the operand data for A through D is stored in four different registers of memory mapped register file 206, N=4 for the number of inputs and outputs for memory mapped register file 206. Accordingly, memory mapped register file 206 uses processor mode inputs 1 through 4 and source index inputs 1 through 4 to obtain encoded addresses for accessing the four registers holding the operand data A through D in memory mapped register file 206 in order to output the operand data as source outputs 1 through 4.
Similarly, if two instructions can be retired from retire logic 210, memory mapped register file 206 can store data from the two retired instructions at a time through write data input 1 and write data input 2. For example, memory mapped register file 206 uses processor mode input 1 and write index input 1 to obtain an encoded address for the register storage location within memory mapped register file 206 for data received at write data input 1. In addition, memory mapped register file 206 uses processor mode input 2 and write index input 2 to obtain an encoded address for the register storage location within memory mapped register file 106 for data received at write data input 2. The manner of processing the above inputs and outputs is explained in further detail below.
FIG. 4 illustrates a block diagram of one example of general purpose registers 400 for memory mapped register file 206. General purpose registers 400 includes sixteen general purpose registers R0 through R15. These registers are associated with register indices ranging from 0000 to 1111 for the sixteen registers. These indices can be used to access the physical general purpose registers 400.
For memory mapped register file 206, the sixteen register indices (0000 through 1111) map to thirty-two encoded addresses (00000 through 11111) for addressing thirty-two registers in memory mapped register file 206. FIG. 5 illustrates a diagram of one example of a memory map 500 of the sixteen general purpose register indices of FIG. 4 to encoded addresses corresponding to thirty-two registers in memory mapped register file 206.
Memory map 500 thus contains thirty-two registers having encoded addresses that map to register indices of general purpose registers 400 in various processor modes. As shown in FIG. 5, each encoded address maps to an index 0000 to 1111 of one of the general purpose registers based on at least one processor mode. In this way, a single memory unit can be used to access storage locations of general purpose registers for different processor modes using the encoded addresses.
This map can be used by encoders to determine encoded addresses using g register index inputs and processor mode inputs for accessing thirty-two registers memory mapped register file 206 associated with general purpose registers. This example, shown in FIG. 5, is based on data processing system 200 being a RISC type system that operates in six different types of processor modes: user mode (USR) mode, fast interrupt request (FIQ) mode, interrupt request (IRQ) mode, supervisor (SVC) mode, undefined instruction (UND) mode, and abort exception (ABT) mode. General purpose registers 400 provides data processing system 200 with sixteen general purpose registers.
As illustrated in memory map 500, registers R0 through R7 having register indices ranging from 0000 to 0111 map to 5-bit encoded addresses ranging from 00000 to 00111. These registers can share the same physical storage location and occupy the first eight storage locations in memory. For example, general purpose register R1 can be addressable using the encoded address 00001.
For general purpose registers R8 through R12, all processor modes except for the FIQ mode share the same memory locations in register file memory unit 600, which are at storage locations addressable by encoded addresses ranging from 11000 through 11111. In the FIQ mode, general purpose registers R8 through R14 are located at storage locations addressable by the encoded addresses 01000 through 01110. Register R15 that is indicated by “Reserved” shares the same memory location for all modes. In this example, R15 can store a program counter (PC). Each of the IRQ, SVC, UND, and ABT modes can access different memory locations to access general purpose registers R13 and R14. Memory map 500 thus details mapping of register indices to their corresponding physical value in memory.
Thus, unlike prior art register files, memory mapped register file 206 uses a single memory unit to access general purpose registers for different processor modes by mapping general purpose register indices to encoded addresses. As a result, general purpose registers used for processor modes such as FIQ, IRQ, SVC, UND, and ABT can be accessed using a single memory unit without using multiple “banked” registers.
FIG. 6 illustrates a detailed circuit diagram of one example of the memory mapped register file 206 of FIG. 3. In this example, memory mapped register file 206 can operate in a multiple issue data processing system, more specifically, a dual issue data processing system. As shown, memory mapped register file 206 includes a register file memory unit 600, a plurality of source address (read) encoders 6021 through 6024, and write address encoders 6101 through 6102.
Register file memory unit 600 is a single memory unit having thirty-two registers and storage locations. The registers are associated with general purpose registers R0 through R14 and R15 (reserved) addressable by encoded addresses 00000 through 11111 for different processor modes in the manner illustrated in memory map 500 of FIG. 5. Memory unit 600 can be implemented as a static random access memory (SRAM) or as a plurality of flip-flops. Register file memory unit 600 is also scalable capable to be capable of having sixty-four registers using 6-bit encoded addresses.
Read encoders 6021 through 6024 receive processor_mode inputs and src1.index through src4.index inputs, respectively, and write encoders 6101 through 6102 receive processor_mode inputs and wr1.index through wr2.index inputs. Read encoders 6021 through 6024 encode a 4-bit source general purpose register index, as shown in memory map 500, to a 5-bit encoded address for accessing a specific register within register file memory unit 600 during a particular processor mode to output source data for instructions. In this example, register file memory unit 600 can output a plurality of source data (src1_data through src4_data) for two instructions.
Read encoders 6021 through 6024 can either latch the encoded addresses in associated latches 6041 through 6044, respectively, or directly output encoded addresses to associated selectors 6061 through 6064, respectively, that also receive as inputs the output of latches 6041 through 6044. Latches 6041 through 6044 latch resultant encoded addresses for pipeline storage of the encoded address in the case that data for an instruction can be reused at the storage location of the latched encoded address. Selectors 6061 through 6064 select either the encoded address directly from the associated address encoders or from the associated latches in response to a signal (not shown) generated by in the instruction decode stage 204. In one example, if one of the selectors 6061 through 6064 selects an encoded address from the associated read address encoder, the encoded address is also latched for pipeline storage. In this manner, the 5-bit encoded address is latched for pipeline storage as opposed to the 4-bit source index, thereby providing further processing efficiency.
Likewise, write encoders 6101 and 6102 each encode a 4-bit source general purpose register index to a 5-bit encoded address for accessing a specific register to write data into register file memory unit 600. In this example, a plurality of write data (wr0_data through wr1_data) can be written into register file memory unit 600. For example, if two instructions can be retired or written back, wr0_data and wr1_data can be written in register file memory 600 at the same time. Register file memory unit 600 can be scalable to have any number of write ports to which any number of data can be applied for writing in the memory mapped register file 206. The manner of reading data from and writing data into general purpose registers of memory mapped register file 206 will now be explained with regards to FIGS. 7 and 8.
FIG. 7 illustrates one example of a flow diagram for a method 700 to output source data from memory mapped register file 206 of FIG. 6. Initially, processor mode and source data index inputs are received (step 702). For example, if an ALU instruction is to be executed in FIQ processor mode that needs values A and B from general purpose registers R8 and R9, the processor mode input would be “FIQ” and the source data index inputs (src1.index and src2.index) would be 1000 and 1001 for registers R8 and R9.
Next, an encoded address is determined based on the received inputs by an address encoder that outputs the encoded address to a latch (step 704). Using the example of memory map 500 above, a source index 1000 maps to encoded address 01000 and source index 1001 maps to encoded address 01001. A selector selects the encoded address stored in the latch or from the address encoder directly (step 706). For instance, selectors 6061 and 6062 can select encoded addresses (01000 and 01001) from either latches 6041 and 6042, respectively, or address encoders 6021 and 6022 directly in which the encoded addresses are outputted to register file memory unit 600. The registers in register file memory unit 600 are then addressed (step 708). In particular, registers R8 and R9 can be addressed using the encoded addresses 01000 and 01001 to access data for registers R8 and R9. Finally, the data A and B at the addressed location are outputted (step 710). That is, the data A and B stored in registers R8 and R9 at encoded addresses 01000 and 01001 are outputted as src1_data and src2_data from register file memory unit 600 to execution stage 204 to execute the ALU operation.
The method shown in FIG. 7 can also be implemented for multiple instructions in which four registers are accessed, assuming there are no data dependencies. For example, if two ALU instructions are required needing values A through D stored in registers R8 through R11 for FIQ mode, the address encoders 6021 through 6024 obtain the encoded addresses 01000 through 01011 from the source indexes 1000 through 1011 for registers R8 through R11. The data values A through D at storage locations addressable by the encoded addresses are outputted as src1_data through src4_data.
FIG. 8 illustrates one example of a flow diagram for a method 800 to write data into memory mapped register file 206 of FIG. 6. Initially, processor mode and write index inputs are received (step 802). In method 800, wr0_data and wr1_data received at write input ports are to be written into two registers (R8 and R9) of register file memory unit 600 during FIQ mode. Thus, the processor mode input would be “FIQ” and the wr0.index would be 1000 and the wr1.index would be 1001.
Next, an encoded address is obtained based on the received inputs (step 804). Using the example of memory map 500 above, wr0.index of 1000 maps to encoded address 01000 and wr1.index of 1001 maps to encoded address 01001. The storage locations in register file memory unit 600 are then addressed based on the encoded addresses (step 806). In particular, registers R8 and R9 can be addressed using the encoded addresses 01000 and 01001 for writing data to registers R8 and R9. Finally, the wr0_data and wr1_data are written into the storage locations addressable by the encoded addresses 01000 and 01001.
Thus, a memory mapped register file has been described. The memory mapped register file described herein can be implemented for general computing devices, examples of which include microprocessors, processors, central processing units (CPUs), application specific integrated circuits (ASICs), system on a chips (SOCs), embedded systems, micro-controllers, and other computing devices. Moreover, the memory mapped register file can be implemented for multi-stage and variable stage pipelining architectures that operate in different processor modes.
Furthermore, in the foregoing specification, the invention has been described with reference to specific exemplary embodiments and implementations thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.

## Claims

1. A register system for a data processing system comprising:
an unbanked memory unit having a plurality of registers addressable by an encoded address, wherein the encoded address corresponds to a respective one of the plurality of registers and a corresponding processor mode;
input ports to receive inputs for addressing at least one register using an encoded address,
output ports to output data from at least one register addressable by an encoded address; and
an address encoder for each of said input ports, the address encoder to provide an encoded address for accessing one of the plurality of registers,
wherein each of the plurality of registers has an address having a length of x bits, each of the processor modes has a length of y bits, and the encoded address has a length that is less than x+y bits.

2. The register system of claim 1, wherein the encoded address identifies a general purpose register associated with a processor mode.

3. The register system of claim 1, wherein each register is associated with a register index that maps to an encoded address based on at least one processor mode.

4. The register system of claim 3, wherein the input ports receive at least one source register index input and processor mode input for use in providing an encoded address for accessing at least one register.

5. The register system of claim 4, wherein data for one or more instructions being processed is outputted from the unbanked memory unit.

6. The register system of claim 3, further comprising:
a latch to latch an encoded address from the address encoder; and
a selector coupled to the latch and the address encoder, the selector to select the encoded address from either the latch or the address encoder.

7. The register system of claim 6, wherein the latch stores the encoded address as a pipeline storage of the encoded address.

8. The register system of claim 3, further comprising:
input ports to receive at least one write index input and processor mode input for use in providing the encoded address for writing data to at least one register; and
at least one write input port for writing the data to the register addressable by the encoded address.

9. The register system of claim 8, wherein data for one or more executed instructions for the data processing are written into the unbanked memory unit.

10. The register system of claim 3, wherein the processor mode includes exception handling modes.

11. The register system of claim 10, wherein the exception handling processor modes include at least one of a fast interrupt request (FIQ) mode, interrupt request (IRQ) mode, supervisor (SVC) mode, undefined instruction (UND), and abort exception (ABT) mode.

12. The register system of claim 11, wherein each exception handling mode corresponds to one or more registers.

13. A register system for a data processing system comprising:
unbanked memory means having a plurality of register means addressable by an encoded address, wherein the encoded address corresponds to a respective one of the plurality of register means and a corresponding processor mode;
a plurality of input means for receiving inputs for addressing at least one register means using an encoded address;
output means for outputting data from at least one register means addressable by an encoded address; and
corresponding addressing means for each of the plurality of input means for providing an encoded address to address one of the plurality of register means,
wherein each of the plurality of register means has an address having a length of x bits, each of the processor modes has a length of y bits, and the encoded address has a length that is less than x+y bits.

14. The register system of claim 13, wherein the encoded address identifies a general purpose register associated with a processor mode.

15. The register system of claim 13, wherein each register means is associated with a register index that maps to an encoded address based on at least one processor mode.

16. The register system of claim 15, wherein the input means further includes means for receiving al least one source register index input and processor mode input for use in providing an encoded address for accessing at least register means.

17. The register system of claim 16, further comprising:
latching means for latching an encoded address from the addressing means; and
selecting means coupled to the latching means and the addressing means for selecting the encoded address from either the latching means or the addressing means.

18. The register system of claim 17, wherein the latching means includes storage means for storing the encoded address as a pipeline storage of the encoded address.

19. The register system of claim 16, wherein data for one or more instructions being processed is outputted from the unbanked memory means.

20. The register system of claim 15, further comprising:
input means for receiving at least one write index input and processor mode input for use in providing the encoded address for writing data to at least one register means; and
at least one write input means for writing the data to the register means addressable by the encoded address.

21. The register system of claim 20, wherein data for one or more executed instructions for the data processing are written into the unbanked memory means.

22. The register system of claim 15, wherein the processor mode includes exception handling modes.

23. The register system of claim 22, wherein the exception handling processor modes include at least one of a fast interrupt request (FIQ mode, interrupt request (rRQ) mode, supervisor (SVC) mode, undefined instruction (UND) mode, and abort exception (ABT) mode.

24. The register system of claim 23, wherein each exception handling mode corresponds to one or more register means.

25. A data processing system comprising: a microprocessor comprising:
a plurality of pipeline stages including a register system, the register system including:
an unbanked memory unit having a plurality of registers addressable by an encoded address, wherein the encoded address corresponds to a respective one of the plurality of registers and a corresponding processor mode;
input ports to receive inputs for addressing at least one register using an encoded address, wherein each of the input ports receives the inputs from a corresponding address encoder; and
output ports to output data from at least one register addressable by an encoded address,
wherein each of the plurality of registers has an address having a length of x bits, each of the processor modes has a length of y bits, and the encoded address has a length that is less than x+y bits.

26. The data processing system of claim 25, wherein the encoded address identifies a general purpose register associated with a processor mode.

27. The data processing system of claim 25, wherein the pipeline stages include:
an instruction fetch stage to fete one or more instructions; and
an instruction decode stage to decode fetched instructions from the instruction fetch stage, the instruction decode stage to forward inputs to the unbanked memory unit for outputting data from or writing data to one or more of the registers.

28. The data processing system of claim 27, wherein the register system further includes:
a plurality of input ports to receive inputs from the instruction decode stage, the inputs being used to obtain the encoded address for accessing at least one register; and
at least one output port to output data from the register addressable by the encoded address.

29. The data processing system of claim 28, wherein the pipeline stages further include:
an execution stage including a plurality of execution units, each execution unit to receive data from the register file for executing an instruction.

30. The data processing system of claim 29, further comprising:
a write back or retire logic stage to receive results data associated with one or more instructions executed by the execution units of the execution stage, and to forward the results data to the register file for storage.

31. The data processing system of claim 30, wherein the register system further includes:
a plurality of input ports to receive the data from the write back or retire logic for one or more executed instructions, the data to be written in the register system.

32. The data processing system of claim 27, wherein each register is associated with a register index that maps to one of the encoded addresses based on at least one processor mode.

33. The data processing system of claim 32, wherein the processor mode includes exception handling modes.

34. The data processing system 33, wherein the exception handling processor modes include at least one of a fast interrupt request (FIQ) mode, interrupt request (IRQ) mode, supervisor (SVC) mode, undefined instruction mode (UND), and abort exception (ABT) mode.

35. The data processing system of claim 34, wherein each exception handling mode corresponds to one or more registers.

36. A data processing system comprising:
a processing means for processing instructions,
a pipeline means for executing instructions, the pipeline means including a register system means, the register system means including:
unbanked memory means having a plurality of register means addressable by an encoded address, wherein the encoded address corresponds to a respective one of the plurality of register means and a corresponding processor mode,
a plurality of input means for receiving inputs for addressing at least one register means using an encoded address;
output means for outputting output data from at least one register means addressable by an encoded address; and
addressing means for each of the plurality of input means for providing an encoded address for accessing one of the plurality of register means,
wherein each of the plurality of register means has an address having a length of x bits, each of the processor modes has a length of y bits, and the encoded address has a length that is less than x+y bits.

37. The data procession system of claim 36, wherein the encoded address identifies a general purpose register associated with a processor mode.

38. The data processing system of claim 36, wherein the pipeline means includes:
fetching means for fetching one or more instructions for execution; and
decoding means for decoding fetched instructions from the fetching means and for forwarding inputs to the unbanked memory means for outputting data from or writing data to one or more of the register means.

39. The data processing system of claim 38, wherein the register system means further includes:
input means for receiving inputs from the decoding means, the inputs being used to obtain the encoded address for accessing at least one register; and
at least one output means for outputting data from the register addressable by the encoded address.

40. The data processing system of claim 39, wherein the pipeline means further includes: an execution means including a plurality of execution processing means, each execution processing means receiving receive data from the register system means for executing an instruction.

41. The data processing system of claim 40, further comprising:
write back means or retire logic means for receiving results data associated with one or more instructions executed by an execution processing means and for forwarding the results data to the register system means for storage.

42. The data processing system of claim 41, wherein the register system means further includes:
a plurality of input means for receiving the data from the write back means or retire logic means for one or more executed instructions, the data to be written in the register system means.

43. The data processing system of claim 38, wherein each register means is associated with a register index that maps to one of the encoded addresses based on at least one processor mode.

44. The data processing system of claim 43, wherein the processor mode includes exception handling modes.

45. The data processing system 44, wherein the exception handling processor modes include at least one of a fast interrupt request (FIQ mode, interrupt request (IRQ) mode, supervisor (SVC) mode, undefined instruction (LJND) mode, and abort exception (ABT) mode.

46. The data processing system of claim 45, wherein each exception handling mode corresponds to one or more register means.

47. A microprocessor comprising:
an integrated circuit comprising:
an unbanked memory unit having a plurality of registers addressable by an encoded address, wherein the encoded address corresponds to a respective one of the plurality of registers and a corresponding processor mode;
a plurality of inputs to receive index and processor mode information for use in providing the encoded address;
at least one output to output data stored in the storage location addressable by the encoded address; and
at least one address encoder for each of the inputs to provide at least one encoded address for addressing at least one of the registers,
wherein each of the plurality of registers has an address having a length of x bits, each of the processor modes has a length of y bits, and the encoded address has a length that is less than x+y bits.

48. The microprocessor of claim 47, wherein the encoded address identifies a general purpose register associated with a processor mode.

49. The microprocessor of claim of claim 47, wherein each register is associated with a register index that maps to the encoded address based on at least one processor mode.

50. The microprocessor of claim 49, wherein the processor mode includes exception handling modes.

51. The microprocessor of claim 50, wherein the exception handling processor modes include at least one of a fast interrupt request (FIQ mode, interrupt request (IRQ) mode, supervisor (SVC) mode, undefined instruction (UND) erode, and abort exception (ABT) mode.

52. The microprocessor of claim 49, further comprising:
at least one write input to receive data to be written into the storage location addressable by the encoded address.

53. A microprocessor comprising:
integrated circuit means comprising:
unbanked memory means having a plurality of register means addressable by an encoded address, wherein the encoded address corresponds to a respective one of the plurality of register means and a corresponding processor mode;
a plurality of input means for receiving index and processor mode information for use in providing the encoded address;
at least one output means for outputting data stored in the storage location addressable by the encoded address; and
at least one addressing means for each of the plurality of input means for providing at least one encoded address for addressing at least one of the register means,
wherein each of the plurality of register means has an address having a length of x bits, each of the processor modes has a length of y bits, and the encoded address has a length that is less than x+y bits.

54. The microprocessor of claim 53, wherein the encoded address identifies a general purpose register associated with a processor mode.

55. The microprocessor of claim of claim 53, wherein each register means is associated with a register index that maps to the encoded address based on at least one processor mode.

56. The microprocessor of claim 55, wherein the processor mode includes exception handling modes.

57. The microprocessor of claim 56, wherein the exception handling processor modes include at least one of a fast interrupt request (FIQ mode, interrupt request (IRQ) mode, supervisor (SVC) mode, undefined instruction (UND) mode, and abort exception (ABT) mode.

58. The microprocessor of claim 57, wherein the exception handling modes correspond to one or more registers.

59. The microprocessor of claim 55, further comprising:
at least one write input means for receiving data to be written into the storage location addressable by the encoded address.

60. An integrated circuit method comprising:
configuring the integrated circuit to receive processor mode and source data inputs;
configuring the integrated circuit to determine an encoded address at one of a plurality of address encoders based on the processor mode and source data inputs, wherein the encoded address corresponds to a respective one of a plurality of unbanked registers and a corresponding processor mode and each of the processor mode and source data inputs corresponds to one of the plurality of address encoders;
configuring the integrated circuit to address one of the unbanked registers using an encoded address; and
configuring the integrated circuit to output data from the unbanked register addressable by the encoded address,
wherein each of the plurality of registers has an address having a length of x bits, each of the processor modes has a length of y bits, and the encoded address has a length that is less than x+y bits.

61. The method of claim 60, further comprising:
configuring the integrated circuit to output data for multiple instructions.

62. The method of claim 60, further comprising:
configuring the integrated circuit to write data to one of the unbanked registers addressable by an encoded address.

63. The method of claim 62, further comprising:
configuring the integrated circuit to write data to one or more unbanked registers for multiple executed instructions.

64. A method for accessing an unbanked memory unit having a plurality of registers comprising:
receiving inputs for accessing the register system;
determining at least one encoded address in accordance with the received inputs at one of a plurality of address encoders, wherein at least one of the plurality of address encoders corresponds to each of the received inputs;
accessing the unbanked memory unit in accordance with the encoded address, wherein the encoded address corresponds to a respective one of the plurality of registers and a corresponding processor mode; and
outputting data from the unbanked memory unit accessed with the encoded address,
wherein each of the plurality of registers has an address having a length of x bits, each of the processor modes has a length of y bits, and the encoded address has a length that is less than x+y bits.

65. The method of claim 64, wherein receiving the inputs includes receiving processor mode inputs and source data inputs.

66. The method of claim 65, wherein determining at least one encoded address includes determining at least one encoded address based on the processor mode inputs and source data inputs.

67. The method of claim 64, wherein outputting data includes outputting data for multiple instructions.

68. The method of claim 64, further comprising:
writing data to at least one of the registers addressable by the encoded address.

69. The method of claim 68, further comprising:
writing write data to the registers for multiple executed instructions.