Resource Files
Reading Assignments
The current reading assignment is Sections 7-12 of Appendix C.
Project Description
The assignment is to construct a register file following the pattern for the MIPS register file covered in Appendix C, section C.8, but scaled down to accommodate the limited number of manual input and output devices on the DE-1 logic kits.
Specifically, your project is to implement a 4×4 register file with two read ports and one write port. Like the MIPS, Register #0 is special: writing to it will do nothing, and reading from it will always produce 4 binary zeros. So there will be just 3 actual registers.
There is a block diagram of the register file in many of the figures in the textbook, including Figure 4.15 on page 320 and Figure C.8.7 on page C-55.
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Set up the project and testbed.
Create a directory name Assignment 5 under the My Projects directory of your roaming profile in the lab. Copy the hex2sevenseg.v file into that directory.
Create a new Quartus project, using “register_file_testbed” as the name of the top-level design entity. Add hex2sevenseg.v to the project. Create a new block diagram file (schematic) for the testbed and set up the I/O pins for it:
You will need two two-bit numbers to select the two registers to be read, another two-bit number to select the register to be written, and a four-bit number to specify the value to be written. Use the ten slide switches for these inputs, in the following order from left to right: Read Register #1; Read Register #2; Write Register #; Write Data. Connect all ten switches to their corresponding Red LEDs; connect Read Register #1 and Read Register #2 to Hex_3; Read Data 1 to Hex_2; Read Data 2 to Hex_1; and Write Register # to Hex_0. There aren’t enough seven-segment displays to show the Write Register Data, so we will have to settle for just the Red LEDs[3:0] to see that.
What is new about this project is the need for a clock signal to trigger the write operation of the register file. Simply set up an input pin named “clock” for this, and connect it to any one of the three clock inputs available on the DE-1. It doesn’t matter which clock signal you use because they all operate way too quickly for you to see any difference during your manual testing of the project.
Finally, use Key_0 as the "write" control signal. Don’t forget to invert it so that pressing it generates a logic 1 value.
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Create a 4-bit register module.
Use 4 dffe (D flip-flop with enable) elements to build the register module. You will find the symbol under “storage” in the Quartus symbol library. The inputs should be clock, enable, data_in[3:0]; the outputs should be data_out[3:0].
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Create a module for the register file.
There should be three two-bit inputs for the three register numbers (Read Register 1; Read Register 2; Write Register), a four-bit input for the Write Data, two four-bit outputs for the two Read Register Data values, a RegWrite input, and a clock input.
There are to be just three register modules inside this module because Register #0 does not actually exist. Use a 2×4 decoder with the Write Register # as inputs to enable the appropriate registers. (Output #0 of the decoder will not connect to anything because there is no Register #0.) Use two 4×4 multiplexers for the read data outputs; connect inputs #0 to ground to implement Register 0.
Connect the clock input to the clock inputs of all three registers. Use the RegWrite input to control whether the decoder outputs actually affect the inputs to the registers.
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Test the register file.
Create a symbol for the register file module, and insert an instance of it into the testbed. Connect the I/O pins to the corresponding pins of the register file.
You should be able to select two registers for reading by using Switches[9..8] and Switches[7:6] to select any pair. Be sure the value displayed in Hex_3 reflects the settings of those four switches. Until you write something into a register, expect the values displayed in Hex_2 and Hex_1 to both be 0. Changing the settings of Switches[5:4] (the write register #) should affect the number displayed in Hex_0; changing the settings of Switches[3:0] (the write data value) should have no effect, except for the corresponding Red LEDs.
Once you have verified that the inputs and outputs are set up correctly, it is time to write some data into the registers. Use Switches[5:4] to select a register number other than zero, and use Switches[3:0] to set up a non-zero data value. Press Key_0 to write the data into the selected register. The same data will be written into the register several million times, depending on how long you hold Key_0 down. Once would be enough, but you can’t press and release the button that fast! After you have written data into a register, use Switches[9:8] and Switches[7:6] to verify that you can read the value out of both read ports: it should show up in Hex_2 and Hex_1. Write different values into different registers, and verify that you can read out any pair of values from any two registers. Be sure you can’t change the value of Register 0 (pressing Key_0 when Switches[5:4] are set to 002 should have no effect; setting Switches[9:8] and/or Switches[7:6] should always produce 0 in Hex_2 and Hex_1 respectively.
Submit
When you have built and tested your assignment let me know it is ready for grading by sending me an email message (Christopher.Vickeryatqc.cuny.edu) by midnight of the due date.
The Subject line of all email you send me this semester must start, “CS-343.’ Your email message for this assignment must be: “CS-343 Assignment 5.”