A first FPGA project - SPI

I wanted to do some projects with a FPGA. Starting out was a little rough, so here are my steps to help you save time.

1) Get the hardware

I got the Max10 evaluation board. What I didn't realize when I ordered the board is that the USB cable is for powering the board only. There is no programmer. The board has a power supply, clock, some LEDs and breakout of the pins.

I got the USB blaster, the cheaper version from Terasic. This lets you program the FPGA.

I had an ATMEGA256RFR2 evaluation board. This board runs the controller at 3.3V, so it is compatible with the Max10 evaluation board. This board is nice because you can program the ATMEGA256RFR2 over usb, and also shows up as a COM port, so you can communicate with the microprocessor from a PC.

Here is the block diagram. The PC connects to the ATMEGA256RFR2 by serial port (serial over USB), and then the ATMEGA256RFR2 will connect to the Max10 FPGA using SPI.

2) Write the software

For the ATMEGA256RFR2, I wrote a program that lets you use the microprocessor from a command-line like perspective. I'll put the code in a post, but the main idea is that from the PC, you can just read/write the registers of the ATMEGA256RFR2. I wrote and programmed the ATMEGA256RFR2 using Atmel Studio 7.0.

For the Max10, you need to install Quartus (Quartus Prime 20.1) Lite Edition. Once you have it installed, you need to create a new, blank project for the target FPGA. In my case, you need to read the part number off of the chip, 10M08SAE144C8G. I'll post the verilog in a post.

3) Run and test

I connect to the ATMEGA256RFR2 using Tera term. Then, I send bytes over SPI using the sequence of register read and writes. The FPGA responds with a simple byte response.

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Main.h

sciencedude1990 • 11/17/2020 at 16:12 • 0 comments

#ifndef MAIN_H_
#define MAIN_H_

// Serial port stuff
#include <string.h>
#include <stdio.h>

// Printing a string to the serial port
void print_serial(const char * const print_string);

// Given an input array, process the command
void go_process_command();

#endif // MAIN_H_

ATMEGA256RFR2 project code

sciencedude1990 • 11/02/2020 at 03:47 • 0 comments

Here is the code for the microcontroller (ATMEGA256RFR2, running at 3.3 V)

#include <avr/io.h>
// LOW.CLKDIV8 is unchecked, and LOW.CKSEL_SUT is Transceiver Oscillator; Start-up time: 16K CK +  65 ms
#define F_CPU 16000000UL
#include <util/delay.h>
#include <avr/interrupt.h>
#include "main.h"

// Place to store a string for USART communication
static char temp_string[64];
// Simple routine to output a serial string to the UART
void print_serial(const char * const print_string) {
    uint8_t temp = 0;
    
    while (temp < strlen(print_string)) {
        if ((UCSR1A & 0x20) == 0) {
            // Do nothing
            _delay_us(10);
        }
        else {
            // Send a byte
            UDR1 = (uint8_t) print_string[temp];
            temp = temp + 1;
        }
    }
    
    // Send ASCII 13 and 10
    temp = 0;
    while (temp < 2) {
        if ((UCSR1A & 0x20) == 0) {
            // Do nothing
            _delay_us(10);
        }
        else {
            if (temp == 0) {
                UDR1 = 13;
            }
            
            if (temp == 1) {
                UDR1 = 10;
            }
            temp = temp + 1;
        }
    }
}

// Place to store the user input
static uint8_t rx_in_buffer[64];
// The count of user input
static uint8_t rx_in_buffer_count = 0;

ISR(USART1_RX_vect) {

    // Read the character from the buffer
    uint8_t temp = UDR1;
    
    // Put the character in the buffer
    rx_in_buffer[rx_in_buffer_count] = temp;
    // Increment the count
    rx_in_buffer_count = rx_in_buffer_count + 1;
    // Count has to be less than 63
    if (rx_in_buffer_count > 63) {
        rx_in_buffer_count = 63;
    }

    // If the character is carriage return, process the command
    if (temp == 13) {
        go_process_command();
    }
}

void go_process_command() {
    // Print some characters in the buffer
    //snprintf(temp_string, 64, "Rx: %d, %d, %d, %d, %d, %d", rx_in_buffer[0], rx_in_buffer[1], rx_in_buffer[2], rx_in_buffer[3], rx_in_buffer[4], rx_in_buffer[5]);
    //print_serial(temp_string);
    
    // The read command
    if ((rx_in_buffer[0] == 114) || (rx_in_buffer[0] == 82)) { // The read command, r or R, expect decimal, for example, expect r72 to read 0x48, OCR0B
        //print_serial("r/R");
        
        // The location of the carriage return
        uint8_t ind_13 = 0;
        
        // Find character 13
        for (uint8_t ii = 1; ii < 64; ii++) {
            if (rx_in_buffer[ii] == 13) {
                ind_13 = ii;
                break;
            }
        }
        // Where character 13 was found
        //snprintf(temp_string, 64, "Char13: %d", ind_13);
        //print_serial(temp_string);
        
        // For processing the register address (convert ASCII characters to addr)
        uint8_t found_it = 0;
        uint16_t addr = 0;
        uint16_t pow_10 = 1;
        
        // If ind_13 was found, build up addr
        if (ind_13 > 1) {
            for (uint8_t ii = (ind_13 - 1); ii > 0; ii--) {
                if ((rx_in_buffer[ii] >= 48) || (rx_in_buffer[ii] <= 57)) {
                    addr = addr + (rx_in_buffer[ii] - 48) * pow_10;
                    pow_10 = pow_10 * 10;
                    found_it = 1;
                }
                else { // Unexpected character
                    found_it = 0;
                    break;
                }
            }
        }
        // Print the address and whether the parsing was as expected
        //snprintf(temp_string, 64, "addr: %u, found_it: %d", addr, found_it);
        //print_serial(temp_string);
        
        // Print the register value
        if (found_it == 1) {
            volatile uint8_t * reg_addr = (uint8_t *) addr;
            uint8_t temp_value = *reg_addr;
            snprintf(temp_string, 64, "Reg: %u = %d, %x", addr, temp_value, temp_value);
            print_serial(temp_string);
        }
    }    
    else if ((rx_in_buffer[0] == 119) || (rx_in_buffer[0] == 87)) { // The write command, w or W, for example, expect w72=4
        //print_serial("w/W");
        
        // The location of the carriage return
        uint8_t ind_13 = 0;
        // Find character 13, carriage return
        for (uint8_t ii = 1; ii < 64; ii++) {
            if (rx_in_buffer[ii] == 13) {
                ind_13 = ii;
                break;
            }
        }
        
        // The location of the =
        uint8_t ind_eq = 0;
        for (uint8_t ii = 1; ii < 64; ii++) {
            if (rx_in_buffer[ii] == 61) {
                ind_eq = ii;
                break;
            }
        }
        
        // Where character = and 13 were found
        //snprintf(temp_string, 64, "Char=: %d, 13: %d", ind_eq, ind_13);
        //print_serial(temp_string);
        
        if ((ind_eq > 1) && ((ind_eq + 1) < ind_13)) {
            // For processing the register address (convert ASCII characters to addr)
            uint8_t found_it = 0;
            uint16_t addr = 0;
            uint16_t pow_10 = 1;
            // Get the register address
            for (uint8_t ii = (ind_eq -...

Code for the FPGA

sciencedude1990 • 10/30/2020 at 18:01 • 0 comments

Here is the code for the FPGA. I noted the pin numbers in at the top...

// Main module - monitor the ports from the microcontroller
module spi_micro_test(
	input wire clk, // 50 MHz clock, pin 27
	input wire bar_ss, // SPI chip select, pin 93
	input wire mosi, // SPI master output, pin 92
	input wire sck, // SPI clock, pin 99
	output wire miso, // SPI sidekick output, pin 101
	output wire led1, // LED1 pin 132
	output wire led2, // LED2 pin 134
	output wire led3, // LED3 pin 135
	output wire led4, // LED4 pin 140
	output wire led5); // LED5 pin 141

//////	
// Observe the serial clock
reg [2:0] sck_r;
initial begin
	sck_r <= 3'b000;
end
always @ (posedge clk) begin
	sck_r <= {sck_r[1:0], sck};
end

// Detect the rising edge
wire sck_risingedge = (sck_r[2:1]==2'b01);
// Detect the falling edge
wire sck_fallingedge = (sck_r[2:1]==2'b10);

//////
// Observe the mosi wire
reg [1:0] mosi_r;

always @ (posedge clk) begin
	mosi_r <= {mosi_r[0], mosi};
end
// The mosi data
wire mosi_data = mosi_r[1];

//////
// Observe bar_ss
reg[2:0] bar_ss_r;
initial begin
	bar_ss_r <= 3'b111;
end

always @ (posedge clk) begin
	bar_ss_r <= {bar_ss_r[1:0], bar_ss};
end

// Detect the rising edge
// wire bar_ss_risingedge = (bar_ss_r[2:1]==2'b01);
// Detect the falling edge
wire bar_ss_fallingedge = (bar_ss_r[2:1]==2'b10);
// Observation of bar_ss
wire bar_ss_observe = bar_ss_r[1];

//////
// Place to store input data
// reg data_ready;
reg [2:0] bit_count;
reg [7:0] data_rx;

//////
// Place to store the output data
reg [7:0] data_tx;

initial begin
	data_tx <= 8'b01100101;
end

// Output is tristate, until bar_ss_observe becomes 0
assign miso = (!bar_ss_observe) ? data_tx[7] : 1'bz;

// Capture the value of the bar_ss input from the microcontroller
always @(posedge clk) begin
	if (bar_ss_fallingedge == 1'b1) begin
		// On the falling edge of bar_ss, clear data ready 
		// data_ready <= 1'b0;
		bit_count <= 3'b000;
	end else if ((bar_ss_observe == 1'b0) && (sck_risingedge == 1'b1)) begin
		// If bar_ss is low and on the rising edge, bring in a bit
		bit_count <= bit_count + 3'b001;
		data_rx <= {data_rx[6:0], mosi_data};
	end else if ((bar_ss_observe == 1'b0) && (sck_fallingedge == 1'b1)) begin
		data_tx <= {data_tx[6:0], data_tx[7]};
	end
	
end

// Set the LED outputs
assign led1 = data_rx[0];
assign led2 = data_rx[1];
assign led3 = data_rx[2];
assign led4 = data_rx[3];
assign led5 = bar_ss_observe;

endmodule

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A first FPGA project - SPI

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