Algorithmic State Machine (ASM) charts are a design tool that allow the specification of digital systems in a form similar to a flow chart. An example of an ASM chart is shown in Figure 1. It represents a circuit that counts the number of bits set to 1 in an n-bit input A (A=an1an2a1a0). The rectangular boxes in this diagram represent the states of the digital system, and actions specified inside of a state box occur on each active clock edge in this state. Transitions between states are specified by arrows. The diamonds in the ASM chart represent conditional tests, and the ovals represent actions taken only if the corresponding conditions are either true (on an arrow labeled 1) or false (on an arrow labeled 0).

Figure 1. ASM chart for a bit counting circuit

In this ASM chart, state S1 is the initial state. In this state the result is initialized to 0, and data is loaded into a register A, until a start signal, s, is asserted. The ASM chart then transitions to state S2, where it increments the result to count the number of 1s in register A. Since state S2 specifies a shifting operation, then A should be implemented as a shift register. Also, since the result is incremented, then this variable should be implemented as a counter. When register A contains 0 the ASM chart transitions to state S3, where it sets an output Done =1 and waits for the signal s to be deasserted.

A key distinction between ASM charts and flow charts is a concept known as implied timing. The implied timing specifies that all actions associated with a given state take place only when the system is in that state when an active clock edge occurs. For example, when the system is in state S1 and the start signal s becomes 1, then the next active clock edge performs the following actions: initializes result to 0, and transitions to state S2. The action right-shift A does not happen yet, because the system is not yet in state S2. For each active clock cycle in state S2, the actions highlighted in Figure 1 take place, as follows: increment result if bit a0=1, change to state S3 if A=0 (or else remain in state S2), and shift A to the right.

The implementation of the bit counting circuit includes the counter to store the result and the shift register A, as well as a finite state machine. The FSM is often referred to as the control circuit, and the other components as the datapath circuit.

Task 1

Write SystemVerilog code to implement the bit-counting circuit using the ASM chart shown in Figure 1 on the DE1-SoC board. Include in your code the datapath components needed, and make an FSM for the control circuit. The inputs to your circuit should consist of an 8-bit input connected to slide switches SW70, a synchronous reset connected to KEY0, and a start signal (s) connected to switch SW9. Use the 50 MHz clock signal provided on the board as the clock input for your circuit. Be sure to synchronize the s signal to the clock. Display the number of 1s counted in the input data on the 7-segment display HEX0, and signal that the algorithm is finished by lighting up LEDR9.

Task 2

We wish to implement a binary search algorithm, which searches through an array to locate an 8-bit value A specified via switches SW . A block diagram for the circuit is shown in Figure 2.

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Figure 2. A block diagram for a circuit that performs a binary search.

The binary search algorithm works on a sorted array. Rather than comparing each value in the array to the one being sought, we first look at the middle element and compare the sought value to the middle element. If the middle element has a greater value, then we know that the element we seek must be in the first half of the array. Otherwise, the value we seek must be in the other half of the array. By applying this approach recursively, we can locate the sought element in only a few steps.

In this circuit, the array is stored in a memory module that is implemented inside the FPGA chip. A diagram of the memory module that we need to create is depicted in Figure 3. In a similar fashion to the first task of lab 2, create a memory that is eight-bits wide and 32 words deep.

Figure 3. The 32 x 8 RAM with address register

To place data into the memory, initialize the memory using the contents of a memory initialization file (MIF) and call it my_array.mif, which then has to be created in the folder that contains the Quartus project. Set the contents of your MIF file such that it contains a sorted collection of integers. Your circuit should produce a 5-bit output L, which specifies the address in the memory where the number A is located. In addition, a signal Found should be set high to indicate that the number A was found in the memory, and set low otherwise.

Perform the following steps:

1. Create an ASM chart for the binary search algorithm. Keep in mind that the memory has registers on its input ports. Assume that the array has a fixed size of 32 elements.
2. Implement the FSM and the datapath for your circuit.
3. Connect your FSM and datapath to the memory block as indicated in Figure 2.
4. Include in your project the necessary pin assignments to implement your circuit on your DE-series board. Use switch SW9 to drive the Start input, use SW₇₀ to specify the value

A, use KEY0 for Resetn, and use the boards 50 MHz clock signal as the Clock input (be sure to synchronize the Start input to the clock). Display the address of the data A, if found, on 7-segment displays HEX1 and HEX0, as a hexadecimal number. Finally, use LEDR9 for the Found signal.

5. Create a file called mif and fill it with an ordered set of 32 eight-bit integer numbers.
6. Compile your design, and then download and test it.
7. Use the SignalTap II functionality of Quartus to verify the contents of your RAM module. Find the Intel SignalTap II tutorial on canvas (SignalTap.pdf) to get started. For your RAM module, youll probably want to probe the data loaded via mif.
8. Demonstrate to your TA.