Introduction of Simple Processor

It is basically an electronic device that consists of ALU (arithmetic logic unit) as well as the control circuitry that is required to function as computer’s CPU. Integrated circuit is known as the microprocessor in this case that interprets as well as executes the instruction of program and also intelligently behave. At a speed of the internal clock the processor operates as well as the number of pulse per second is depend on the speed of clock. The processor perform the function that is related to the instruction, with each pulse of clock. 

Figure1: Aim and Objective of report

The basic modules that is used together to make the16 bit microprocessor. (Gupta, 2014) Through different sections the processor uses 16 bit bus to data communicate such as general purpose registers, ALU, Control unit (CU), Memory, Comparator, counter program, register address, instruction & shift registers. (Vaman & k, 2012).In integrated circuit with the advancement of technology the processor power is increased enormously. In the embedded sector the microprocessor is widely used and depend on purpose of general 

application. Using behavioral coding, in instruments microprocessor are used to make it intelligent. In VHDL, in the design all the modules are coded, with its concepts it is a very useful tool to cope with the parallelism concurrency of digital hardware. (D.B.Rane & G, 2014).

The main purpose of this project is that to write the VHDL behavioral model. For this we also build the test bench and simulate the behavior. On FPGA platform same as implement to validate the functionality. Using Xilinx ISE synthesizing it. Using the Spartan family of FPGA we used in this project.

System Requirements  of Simple Processor

                                i.            Arithmetic Logic Unit (ALU)

                              ii.            Comparator

                            iii.            Control Unit (CU)

                            iv.            Register

                              v.            Register Array

                            vi.            Shift Register

                          vii.            Triregister

                        viii.            Programme Counter (PC)

Block Diagram of Simple Processor

It is commonly known as programmable device which accepts digital data inputs, according to the instruction process it stored in its memory and as output provide the results. As a programmable logic device it can be viewed that to control the processes it could be used or else off the devices. As a data processing unit the microprocessor could be viewed or also computing unit of the computer. In a wide range of product microprocessor is used now a days called as a product based on microprocessor. Our objective is to design a 16 bit microprocessor by using VHDL language. This project is very informative. This language is also used for general purpose and this language has several features. To design a small CPU our main goal of this project is to tie all of these features together, verify the functionality which could be synthesized.

 

Figure2: Processor Block Diagram

The figure shows the block diagram of the processor of 16 bit microprocessor. A number of basic pieces are hold by the processor. In 16 bit registers there is a register array of eight, a shifter, there is an arithmetic as well as logic unit, a program counter, an IR (instruction register) , comparator, an AR (address register), as well as a control unit. Through a common 16 bit tristate data all of these blocks connected(Kaliamurthy & Sowmmiya).

Description of System Requirement of Simple Processor

Arithmetic Logic Unit (ALU)

In the ALU there are the two kinds of the operations the first one is 16-bit Arithmetic operations like the subtraction, addition, multiplications and the divisions. And the second is related to the Gate results like the OR, AND, XOR, NAND, which is refereed to logic unit. FPGA design and implementation is based on the ALU, in the importance of the digital technologies where the integral part of CPU.ALU is capable to operate a wide variety of operations, like the arithmetic and the logic. (Sharma & et.al, 2016)

                                                                                  

The block diagram of ALU is shown in below figure 3; in this diagram the blocks of ALU contains the Arithmetic operations; logic; shifter; and the multiplier. ALU is the fundamental block of processors. And the code of the Arithmetic operations is shown as below appendix 1.    (Fpga4student.com, 2018)

Figure4: Block Diagram of ALU

Flowchart of Arithmetic logic unit is as follow

                                                        

Comparator of Simple Processor

Comparison among two values, and returns the 1 and 0 according to their types. Comparison of the values is selected through its input is sel. Input a and b are equal then applied to the port sel, where a and b have the same values, then the output ports returns the 1. And if a and b are not equal then the outputs returns to 0.

The below table 1 display the types of comparisons with values, where the operations works as the inputs values plus return the single bit output. During Simple Processor the flow of operations is controlled by using the bit as compare to executing the instruction. If the test conditions is true then the output return the value “1” that is assigned; otherwise “0”, as the every statement occurred after 1 nanosecond.

Sell-Input Value	Output
EQ	1 when a=b
NEQ	1 when a / =b
GT	1 when a > =b
GTE	1 when a<b
LT	1 when a<=b

Now the VHDL Code of the 16-bit Comparator is shown in the appendix 2 with the test bench and the waveform.

                                                                           

Control Unit of Simple Processor

For the operations of the computer control unit generates timing along with control signals. With arithmetic logic unit along with main memory the control unit communicates. The transmission among processor also control, the various peripherals as well as memory. ALU also instructs data that operations has to be performed.  There is the two method to design a control unit that we describe below; (Studytonight.com, 2018)

                                                 

Hardwired control unit:

With the help of gates, flip flop decoders it is implemented in the hardware. The instruction register, flags, timing signals are the inputs of control unit. If we have to make the large control unit then this organization might be complicated. If we try to modify the design for this we have to change the all logic combinational circuits that is a very difficult task.

                                                               

Figure5: Hardwired control unit

Micro programmed control unit:

Programming approach is another techniques for implementation. During the execution of program there are number of micro operation are carried that consists on the micro instructions. By updating the micro program in control memory via programmer in this organization any modification or changes could be done.

Registers of Simple Processor

When the designing of Simple processor is working, then there are various types of register is used; like the

·         Array register

·         Instruction Register

·         Shift Register

·         Triregister  

The block of register is used to address the register plus for the instruction register, and these register are used to capture the data for the clock input and drive the output for the captured data. The rising edge  register have the three ports, port 1 is the input port , and the port 2 is output port , and the third port is clk (clock)port which control the data for the stored register as the entity. At the input clock where the rising edge occur then the value of inputs is assigned to output q. Its takes the nanoseconds for the delay to remove the delta during simulations

Segment of the array registers is sued for the set of registers in the processors which is used to store the intermediate values in instructions. In array register write the location to set the input sel (select) for the written locations, in the input data, to assign the rising edge for the input clk.

To store the instruction which is being fetched from a memory, the instruction register is used. For a current situations the, the PC (Programme Counter) holds the address of the memory. When the instructions is completed, then the PC move for the instructions. Then the PC is loaded, if the branch of instruction, is addressed by the next instructions, then the value of the PC is copied by a control unit; to address the register. (Gupta & et.al, Analysis of 16 Bit Microprocessor Architecture on FPGA Using VHDL, 2014)

                                  

Source: https://www.researchgate.net/publication/228639753_MIB-16_FPGA_Based_Design_and_Implementation_of_a_16-Bit_Microprocessor_for_Educational_Use

Figure6: Register Structure

Programme Counter of Simple Processor

Instruction is being executed by keeping the counter program. Mostly counter program holds the address of next instruction that might be executed. When the first execution is started then it is incremented one by one to the next state. As a result, program counter is always made to execute the next instruction in an order. This is a special purpose register. For the microprocessor a functional level block diagram of the program counter is designed below.

                           

 References of Simple Processor

D.B.Rane, & G, P. P. (2014). “Design and performance analysis of 16-bit RISC processor”. ISSN.

Fpga4student.com. (2018). 16-bit ALU Design in VHDL. Retrieved from https://www.fpga4student.com/2017/07/16-bit-alu-design-in-vhdl.html

Gupta, N. (2014). “Analysis of 16 bit microprocessor architecture on Fpga using VHDL”. Advanced Research in Electrical.

Gupta, N., & et.al. (2014, April). Analysis of 16 Bit Microprocessor Architecture on FPGA Using VHDL. International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering, 3(4), 8979-8986.

Kaliamurthy, & Sowmmiya, U. (n.d.). VHDL design of FPGA arithmetic processor. Global journal of researches in engineering, 11(5), 2249-4596.

Sharma, P., & et.al. (2016, August). A Review: Design of 16 bit Arithmetic and Logical unit using Vivado 14.7 and Implementation on Basys 3 FPGA Board. International Journal for Research in Applied Science & Engineering Technology (IJRASET), 4(VIII), 453-460. Retrieved from https://www.ijraset.com/fileserve.php?FID=5343

Studytonight.com. (2018). Design of Control Unit. Retrieved from https://www.studytonight.com/computer-architecture/design-of-control-unit

Vaman, S., & k, S. (2012). “Design of FPGA based 16 bit pipelined RISC controller IP core using VHDL". ISBN.