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Understanding Registers in Computer Architecture

Learn about registers, a small storage in CPUs, their role in RAM data management, and building a register file using VHDL in this detailed guide.

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Understanding Registers in Computer Architecture

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  1. Lab 05 Sen Ma

  2. What is a Register ? “In computer architecture, a register is a small amount of storage available as part of a CPU. ” --Wikipedia

  3. What is Register ? “In computer architecture, a register is a small amount of storage available as part of a CPU. ” --Wikipedia Data in the Random-access memory (RAM)

  4. What is Register ? “In computer architecture, a register is a small amount of storage available as part of a CPU. ” --Wikipedia Data in the Random-access memory (RAM) Registers are stored in a structure called a register file which impalement by using RAM.

  5. What is Register ? Register File’s name Reg_File Assume we have 10 registers. R0 ~ R9 Each register has 16bits. Another assumption R0 = 0 and R1 = 1 (forever)

  6. What is Register ? Reg_File Oh Yeah, we have registers! We can design our own instructions How about this: R2 = R0 + R1

  7. What is Register ? Reg_File Oh Yeah, we have registers! We can design our own instructions How about this: R2 = R0 + R1 R2 = R0 + R1

  8. What is Register ? Reg_File Oh Yeah, we have registers! We can design our own instructions How about this: R2 = R0 + R1 R2 = R0 + R1

  9. What is Register ? Reg_File Oh Yeah, we have registers! We can design our own instructions How about this: R2 = R0 + R1 R2 = R0 + R1 We have already know the assembly language: R2 = R0 + R1 add R2, R0, R1

  10. What is Register ? Reg_File One more! add R3, R1, R2

  11. What is Register ? Reg_File One more! add R3, R1, R2

  12. What is Register ? Reg_File Behind the scene: You can think about the Reg_File is an Array. When you read from or write in the register, it is same operation on an array which you have already know.

  13. What is Register ? Register File’s name (array’s name) Reg_File Same Example: add R3, R1, R2 1 step, Read R1: Reg_File[1]

  14. What is Register ? Reg_File Same Example: add R3, R1, R2 1 step, Read R1: Reg_File[1] 2 step, Read R2: Reg_File[2]

  15. What is Register ? Reg_File Same Example: add R3, R1, R2 1 step, Read R1: Reg_File[1] 2 step, Read R2: Reg_File[2] 3 step Add Reg_File[1] + Reg_File[2]

  16. What is Register ? Reg_File Same Example: add R3, R1, R2 1 step, Read R1: Reg_File[1] 2 step, Read R2: Reg_File[2] 3 step Add Reg_File[1] + Reg_File[2] 4 step, Write R3: Reg_File[3] = Reg_File[1] + Reg_File[2]

  17. Register in VHDL Define an array in VHDL: type ram_type is array (15 downto 0) of std_logic_vector(15 downto 0); Reg_File

  18. Register in VHDL Define an array in VHDL: typeram_type is array (15 downto 0) of std_logic_vector(15 downto 0); Reg_File Define a type named “ram_type” which is a array with 16 item. Each item is a 16bits vector

  19. Register in VHDL Define an array in VHDL: typeram_type is array (15 downto 0) of std_logic_vector(15 downto 0); signalReg_File : ram_type; Reg_File Using the “ram_type” to define a signal named “Reg_File”.

  20. Register in VHDL Define an array in VHDL: typeram_type is array (15 downto 0) of std_logic_vector(15 downto 0); signalReg_File : ram_type; Reg_File Same Example: add R3, R1, R2 Reg_File(3) <= Reg_File(1) +Reg_File(2);

  21. Register clk b_data clear c_data A_addr A_data load b_addr c_addr

  22. Register Entity Register is port( clk: instd_logic; -- positive edge triggered clock clear: instd_logic; -- asynchronous reset a_addr: instd_logic_vector( 3 downto 0); -- input data port a_data: instd_logic_vector(15 downto 0); -- register select for input a load: instd_logic; -- load enable b_addr: instd_logic_vector( 3 downto 0); -- register select for output b c_addr: instd_logic_vector( 3 downto 0); -- register select for output c b_data: out std_logic_vector(15 downto 0); -- first output data port c_data: out std_logic_vector(15 downto 0) -- second output data port ); End Register;

  23. Register Requirements: • Create a register file. • It should have 16 registers, each being sixteen bits wide. • When the load signal is asserted, a rising edge on clk cause the data on a_data to be stored in the register identified by a_addr. • If the load signal is not asserted, a rising clock edge has no effect. • The data on b_data should be the contents of the register identified by b_addr. • The data on c_data should be the contents of the register identified by c_addr. • Register 0 always contains the value 0. Writing to register 0 is ignored. • Register 1 always contains the value 1. Writing to register 1 is ignored. • When the clear signal is 0, all registers (other than register 1) are reset to 0. Note that this is asynchronous. • Follow the instruction on page 129~130 in Xilinx XST User Guide, reference the example code to implement your own register file.

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