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Raspberry Pi + Arduino + SPI

Posted by meyers on Aug 11, 2012 in Arduino, Raspberry Pi, Tutorials | 31 comments

This worked for me.

This tutorial will show you how to communicate from your raspberry pi to your arduino using 3-wire SPI.

Requirements

1 Raspberry pi (running Raspbian)
1 Arduino
4 wires

Your raspberry pi should be running the newest version of Raspbian. To ensure your system is up-to-date please download and run rpi-update.

Wiring

Arduino

Open your Arduino ide and flash the below code to your Arduino.

Arduino code

// Written by Nick Gammon // February 2011 /** * Send arbitrary number of bits at whatever clock rate (tested at 500 KHZ and 500 HZ). * This script will capture the SPI bytes, when a '\n' is recieved it will then output * the captured byte stream via the serial. */ #include <SPI.h> char buf [100]; volatile byte pos; volatile boolean process_it; void setup (void) { Serial.begin (115200); // debugging // have to send on master in, *slave out* pinMode(MISO, OUTPUT); // turn on SPI in slave mode SPCR |= _BV(SPE); // get ready for an interrupt pos = 0; // buffer empty process_it = false; // now turn on interrupts SPI.attachInterrupt(); } // end of setup // SPI interrupt routine ISR (SPI_STC_vect) { byte c = SPDR; // grab byte from SPI Data Register // add to buffer if room if (pos < sizeof buf) { buf [pos++] = c; // example: newline means time to process buffer if (c == '\n') process_it = true; } // end of room available } // end of interrupt routine SPI_STC_vect // main loop - wait for flag set in interrupt routine void loop (void) { if (process_it) { buf [pos] = 0; Serial.println (buf); pos = 0; process_it = false; } // end of flag set } // end of loop

Raspberry Pi

With your updated rasbian system you should have the drivers that you need. Now it’s time to load them.

modprobe spi_bcm2708
modprobe spidev

Check to be sure the modules loaded:

lsmod
Module Size Used by
spidev 5944 0
spi_bcm2708 5350 0
snd_bcm2835 21681 0
snd_pcm 81170 1 snd_bcm2835
snd_seq 59528 0
snd_timer 21602 2 snd_seq,snd_pcm
snd_seq_device 6924 1 snd_seq
snd 57427 5 snd_seq_device,snd_timer,snd_seq,snd_pcm,snd_bcm2835
snd_page_alloc 5343 1 snd_pcm
i2c_bcm2708 3822 0

Raspberry Pi Code

Save the below code as spidev_test.c on to your Raspberry Pi and compile it

gcc spidev_test.c -o spidev_test

/* * SPI testing utility (using spidev driver) * * Copyright (c) 2007 MontaVista Software, Inc. * Copyright (c) 2007 Anton Vorontsov <avorontsov@ru.mvista.com> * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License. * * Cross-compile with cross-gcc -I/path/to/cross-kernel/include */ #include <stdint.h> #include <unistd.h> #include <stdio.h> #include <stdlib.h> #include <getopt.h> #include <fcntl.h> #include <sys/ioctl.h> #include <linux/types.h> #include <linux/spi/spidev.h> #define ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0])) static void pabort(const char *s) { perror(s); abort(); } static const char *device = "/dev/spidev0.0"; static uint8_t mode; static uint8_t bits = 8; static uint32_t speed = 500000; static uint16_t delay; static void transfer(int fd) { int ret; uint8_t tx[] = { 0x48, 0x45, 0x4C, 0x4C, 0x4F, 0x20, 0x57, 0x4F, 0x52, 0x4C, 0x44, 0x0A }; uint8_t rx[ARRAY_SIZE(tx)] = {0, }; struct spi_ioc_transfer tr = { .tx_buf = (unsigned long)tx, .rx_buf = (unsigned long)rx, .len = ARRAY_SIZE(tx), .delay_usecs = delay, .speed_hz = speed, .bits_per_word = bits, }; ret = ioctl(fd, SPI_IOC_MESSAGE(1), &tr); if (ret < 1) pabort("can't send spi message"); /* for (ret = 0; ret < ARRAY_SIZE(tx); ret++) { if (!(ret % 6)) puts(""); printf("%.2X ", rx[ret]); } puts(""); */ } static void print_usage(const char *prog) { printf("Usage: %s [-DsbdlHOLC3]\n", prog); puts(" -D --device device to use (default /dev/spidev1.1)\n" " -s --speed max speed (Hz)\n" " -d --delay delay (usec)\n" " -b --bpw bits per word \n" " -l --loop loopback\n" " -H --cpha clock phase\n" " -O --cpol clock polarity\n" " -L --lsb least significant bit first\n" " -C --cs-high chip select active high\n" " -3 --3wire SI/SO signals shared\n"); exit(1); } static void parse_opts(int argc, char *argv[]) { while (1) { static const struct option lopts[] = { { "device", 1, 0, 'D' }, { "speed", 1, 0, 's' }, { "delay", 1, 0, 'd' }, { "bpw", 1, 0, 'b' }, { "loop", 0, 0, 'l' }, { "cpha", 0, 0, 'H' }, { "cpol", 0, 0, 'O' }, { "lsb", 0, 0, 'L' }, { "cs-high", 0, 0, 'C' }, { "3wire", 0, 0, '3' }, { "no-cs", 0, 0, 'N' }, { "ready", 0, 0, 'R' }, { NULL, 0, 0, 0 }, }; int c; c = getopt_long(argc, argv, "D:s:d:b:lHOLC3NR", lopts, NULL); if (c == -1) break; switch (c) { case 'D': device = optarg; break; case 's': speed = atoi(optarg); break; case 'd': delay = atoi(optarg); break; case 'b': bits = atoi(optarg); break; case 'l': mode |= SPI_LOOP; break; case 'H': mode |= SPI_CPHA; break; case 'O': mode |= SPI_CPOL; break; case 'L': mode |= SPI_LSB_FIRST; break; case 'C': mode |= SPI_CS_HIGH; break; case '3': mode |= SPI_3WIRE; break; case 'N': mode |= SPI_NO_CS; break; case 'R': mode |= SPI_READY; break; default: print_usage(argv[0]); break; } } } int main(int argc, char *argv[]) { int ret = 0; int fd; parse_opts(argc, argv); fd = open(device, O_RDWR); if (fd < 0) pabort("can't open device"); /* * spi mode */ ret = ioctl(fd, SPI_IOC_WR_MODE, &mode); if (ret == -1) pabort("can't set spi mode"); ret = ioctl(fd, SPI_IOC_RD_MODE, &mode); if (ret == -1) pabort("can't get spi mode"); /* * bits per word */ ret = ioctl(fd, SPI_IOC_WR_BITS_PER_WORD, &bits); if (ret == -1) pabort("can't set bits per word"); ret = ioctl(fd, SPI_IOC_RD_BITS_PER_WORD, &bits); if (ret == -1) pabort("can't get bits per word"); /* * max speed hz */ ret = ioctl(fd, SPI_IOC_WR_MAX_SPEED_HZ, &speed); if (ret == -1) pabort("can't set max speed hz"); ret = ioctl(fd, SPI_IOC_RD_MAX_SPEED_HZ, &speed); if (ret == -1) pabort("can't get max speed hz"); printf("spi mode: %d\n", mode); printf("bits per word: %d\n", bits); printf("max speed: %d Hz (%d KHz)\n", speed, speed/1000); transfer(fd); close(fd); return ret; }

Running

Plug your Arduino to your desktop via the serial cable. Open the arduino Serial Monitor and set the bitrate to 115200. Now, on the Raspberry Pi, run the compiled code

sudo ./spidev_test

You should see HELLO WORLD print in the Arduino IDE Serial Monitor.

Debugging

Make sure that your kernel has the required drivers (spi-bcm2708.ko and spidev.ko)

pi@raspberrypi ~/spi $ ls -al /lib/modules/`uname -r`/kernel/drivers/spi/
total 64
drwxrwxr-x 2 pi pi 4096 Aug 10 10:53 .
drwxrwxr-x 23 pi pi 4096 Aug 10 10:53 ..
-rw-rw-r– 1 pi pi 14428 Aug 10 10:53 spi-bcm2708.ko
-rw-rw-r– 1 pi pi 10852 Aug 10 10:53 spi-bitbang.ko
-rw-rw-r– 1 pi pi 15803 Aug 10 10:53 spidev.ko
-rw-rw-r– 1 pi pi 10693 Aug 10 10:53 spi-gpio.ko

Thanks to Nick Gammon for the SPI slave code.

Thanks to Anton Vorontsov for the kernel Documentation spidev_test.c example code.

31 Comments

Eric Clarke
August 13, 2012

Wow, can the 3.3V RPi tolerate the 5V TTL levels of the Arduino?

reply
- meyers
  August 13, 2012
  
  Hmm from http://elinux.org/RPi_Low-level_peripherals “The pins use a 3V3 logic level and are not tolerant of 5V levels, such as you might find on a 5V powered Arduino.”.
  Let me try and find out from some friends and colleagues why this works and doesn’t blow up
  
  reply
  - Julian
    August 19, 2012
    
    Accidentally put 5V on the GPIO Pins of mine and didn’t blow up either
    
    reply
    - Lo
      October 1, 2012
      
      Put -5V on it and it’s in the heaven now
      
      reply
    - even
      October 16, 2012
      
      “Non tolerant” doesn’t mean it will blow up right away, just shorten the Pi’s life span. Use a logic level converter like http://www.adafruit.com/products/395 to supply the right voltage levels.
      
      reply
      - TJ
        March 21, 2013
        
        Many N-Channel Enhancement Mode MOSFETs can also be used for level shifting, some of them costing only the loose change in your back trouser pocket.
Frank
August 19, 2012

It might work only because the example doesn’t send any information from the Arduino back to the Pi and thus putting 5v on the Pi input pin.

reply
anjz
August 22, 2012

First of all thank you for sharing this code!

I am new in this, and i would like to know how can the arduino send back the data received to the raspberry.

Thanks!

reply
- Zaxd
  August 23, 2012
  
  I second anjz!
  This would be much more useful
  
  reply
  - Jotschi
    September 5, 2012
    
    I third anjz!
    I’m still searching for a way to work this out. The arduino spi lib itself supports only master mode.
    
    reply
akanto
September 16, 2012

Maybe a bus switch from 5V to 3.3V could be useful in order to avoid harming the Raspberry Pi. Something like this: http://www.ti.com/lit/ds/symlink/sn74cbtd3384c.pdf

reply
wally
October 10, 2012

It would be interesting to learn how the spi-kernel-driver might be used to
read an SPI ADC (e.g. ADS1100). Additionally this would be more save for the hardware, because this ADC works on 2.7 to 5.5V. Where to find more documentation and/or examples using this kernel-driver ? Thank you!

reply
- wally
  October 11, 2012
  
  ADS1100 is rather I2C:
  http://www.ti.com/lit/ds/symlink/ads1100.pdf
  MCP3004/3008 is SPI:
  http://www.adafruit.com/datasheets/MCP3008.pdf
  
  reply
venkatesh
December 17, 2012

im beginner doing spi interface. i tried with above code to start learning. i connected wires as described but i got o/p “can’t able open device”. one thing which is different from above of mine is the broadcom pheripheral mine is BCM2835. is there any change in the code for my bcm. and one more thing spi may be blacklisted when i google for solution how to unlock them. and not able to find spidev under dev. how to resolve it?

reply
- meyers
  December 17, 2012
  
  You can observe the blacklisting or not of the spi drivers by following the guide above. Specifically, the lsmod section. Don’t think of blacklisting a driver as locking but rather as a convenience mechanism for specifying that a driver not be loaded when the distribution starts up for one reason or another.
  
  After you have verified the driver is loaded ensure that the driver created the device nodes. Specifically /dev/spidev0.0
  
  Let me know if you have further problems.
  
  reply
  - venkatesh
    December 17, 2012
    
    when i try lsmod, i cant find spidev0.0 how to load it. please guide me. for lsmod i got this
    
    Module Size Used by
    evdev 8682 4
    joydev 9102 0
    snd_bcm2835 12808 0
    snd_pcm 74834 1 snd_bcm2835
    snd_seq 52536 0
    snd_timer 19698 2 snd_seq,snd_pcm
    snd_seq_device 6300 1 snd_seq
    snd 52489 5 snd_seq_device,snd_timer,snd_seq,snd_pcm,snd_bcm2835
    snd_page_alloc 4951 1 snd_pcm
    
    reply
    - venkatesh
      December 18, 2012
      
      now i got spi enabled
      
      Module Size Used by
      snd_bcm2835 12808 0
      snd_pcm 74834 1 snd_bcm2835
      snd_seq 52536 0
      snd_timer 19698 2 snd_seq,snd_pcm
      snd_seq_device 6300 1 snd_seq
      snd 52489 5 snd_seq_device,snd_timer,snd_seq,snd_pcm,snd_bcm2835
      snd_page_alloc 4951 1 snd_pcm
      spidev 5136 0
      evdev 8682 4
      joydev 9102 0
      spi_bcm2708 4401 0
      
      and in ls /dev/spi*
      
      /dev/spidev0.0 /dev/spidev0.1
      
      now im getting output
      “can’t open device : permission denied”
      
      reply
      - meyers
        December 18, 2012
        
        Try prepending the command you are running with sudo. For example if you are running the command ‘ls’ try ‘sudo ls’.
      - venkatesh
        December 19, 2012
        
        had u wrote code for receiving data from arduino?
meyers
December 19, 2012

Arduino example spi receiver code is included in The above tutorial.

reply
- venkatesh
  December 20, 2012
  
  two things i want to clarify with you. im sending command byte 0xFE from rpi after its received in arduino im sending {0xAA,0xAB,0xAC} from arduino
  
  1. while transmitting a buffer why its necessary to add 0x0A at the end of the buffer (arduino) when i look at serial monitor it shows 0xAA,0xAB,0xAC “0x0A” 0xAA,0xAB,0xAC if 0x0A is added it sendinding as 0xAA,0x0A,0xAB,0x0A.
  
  2.while receiving in rpi, each received byte in sent buffer follwed by command byte(0xFE) for 9 times. eg: if im receiving in rpi as 0xAA 0xFE 0xFE 0xFE 0xFE 0xFE 0xFE 0xFE 0xFE 0xFE 0xAB…….
  
  reply
  - venkatesh
    December 20, 2012
    
    sorry in 1. if 0x0A is not added it sending as 0xAA,0x0A,0xAB,0x0A.
    
    reply
TT
January 16, 2013

I am pretty new to programming. I have a device which I want to connect to the RPi using SPI. I tried out the spi_devtest.c and it works. But the SPI frame of the slave device requires 24 bits. I have searched high and low and have not been able to find a solution. I tried changing the number of bits per word but that does not work. I wonder if I would have to just send 3 bytes instead of 24 bits. In that case, I don’t know how to send 3 bytes without the chip select going inactive after each word. Any help would be greatly appreciated.

reply
- TT
  January 16, 2013
  
  nevermind. i figured it out. thanks anyways
  
  reply
  - pi-ray
    March 8, 2013
    
    TT or anyone. I have the same issue of requiring 24 bits without raising syncb. Do tell how you “figured it out”. Wondering if I can use a different gpio bit and create and control my own sincb, but this seems ugly.
    
    reply
    - TT
      April 16, 2013
      
      Sorry for taking so long to respond, I ended up just sending 3 8bit words. I don’t know if there’s any other way to do it, or if there exists a better way.
      
      reply
venkatesh
January 24, 2013

why the byte being returned back to rpi which sent to arduino? is any voltage converter required?

reply
bocius
February 1, 2013

Hey,

I have some errors while compiling the RasPi code..

They are:
pi@raspberrypi ~ $ gcc spidev_test.c -o spidev_test
spidev_test.c:234:13: error: redefinition of ‘pabort’
spidev_test.c:26:13: note: previous definition of ‘pabort’ was here
spidev_test.c:240:20: error: redefinition of ‘device’
spidev_test.c:32:20: note: previous definition of ‘device’ was here
spidev_test.c:242:16: error: redefinition of ‘bits’
spidev_test.c:34:16: note: previous definition of ‘bits’ was here
spidev_test.c:243:17: error: redefinition of ‘speed’
spidev_test.c:35:17: note: previous definition of ‘speed’ was here
spidev_test.c:246:13: error: redefinition of ‘transfer’
spidev_test.c:38:13: note: previous definition of ‘transfer’ was here
spidev_test.c:279:13: error: redefinition of ‘print_usage’
spidev_test.c:71:13: note: previous definition of ‘print_usage’ was here
spidev_test.c:295:13: error: redefinition of ‘parse_opts’
spidev_test.c:87:13: note: previous definition of ‘parse_opts’ was here
spidev_test.c:364:5: error: redefinition of ‘main’

I got the /dev/spidev0.0 and spidev0.1. The RasPi is updated and everything is ok, except the “pi@raspberrypi ~/spi $ ls -al /lib/modules/`uname -r`/kernel/drivers/spi/” part, where I only get: “total 64″.

Please, help:)

reply
Charles-henri hallard
February 13, 2013

Hello,
Great tuto, just may be asking a stupid question but there is no wire with CE0 ou CE1 between the Arduino and the PI, does the arduino hardware SPI work even if the Chip Enable pin is floating ?
Thanks

reply
fileneed
February 19, 2013

this shows great potential for fast raspi to arduino transfers! what is the fastest this can work?

reply
TT
April 22, 2013

I get this error: spi_slave.ino: In function ‘void setup()’:
spi_slave:24: error: ‘SPCR’ was not declared in this scope
spi_slave:24: error: ‘SPE’ was not declared in this scope
spi_slave:24: error: ‘_BV’ was not declared in this scope
spi_slave.ino: In function ‘void SPI_STC_vect()’:
spi_slave:39: error: ‘SPDR’ was not declared in this scope
Does anyone know what could be the problem and/or know how to fix this? I’m using this code with the arduino due

reply

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Raspberry Pi + Arduino + SPI

Requirements

Wiring