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Raspberry Pi + Arduino + SPI

Posted by meyers on Aug 11, 2012 in Arduino, Raspberry Pi, Tutorials | 48 comments

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.

Eric Clarke

Wow, can the 3.3V RPi tolerate the 5V TTL levels of the Arduino?
- meyers
  
  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 🙂
  - Julian
    
    Accidentally put 5V on the GPIO Pins of mine and didn’t blow up either 😉
    - Lo
      
      Put -5V on it and it’s in the heaven now 😀
    - even
      
      “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.
      - TJ
        
        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

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.
anjz

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

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
wally

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!
- wally
  
  ADS1100 is rather I2C:
  http://www.ti.com/lit/ds/symlink/ads1100.pdf
  MCP3004/3008 is SPI:
  http://www.adafruit.com/datasheets/MCP3008.pdf
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venkatesh

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?
- meyers
  
  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.
  - venkatesh
    
    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
    - venkatesh
      
      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”
      - meyers
        
        Try prepending the command you are running with sudo. For example if you are running the command ‘ls’ try ‘sudo ls’.
      - venkatesh
        
        had u wrote code for receiving data from arduino?
    - parvathi
      
      how did u get spi enabled? when i am trying to install spi_bcm2708 i am getting “unable locate package spi_bcm2708″… please guide me..
meyers

Arduino example spi receiver code is included in The above tutorial.
- venkatesh
  
  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…….
  - venkatesh
    
    sorry in 1. if 0x0A is not added it sending as 0xAA,0x0A,0xAB,0x0A.
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TT

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.
- TT
  
  nevermind. i figured it out. thanks anyways 🙂
  - pi-ray
    
    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.
    - TT
      
      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.
venkatesh

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

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:)
Charles-henri hallard

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
fileneed

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

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
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parvathi

when i am running this code i am getting output as “cant open device” in the raspberry pi terminal.. please help me..
pi

when i am trying to run the raspberry pi code iam getting the error ‘cant open the device’. please guide me…
Aadil

Hi, awesome job here!! I got this working nicely. I am working on a new pi project that is coded in C++ and I am having issues integrating. I’ve tried linking the the above pi C code to my C++ code but get “undefined reference” to the C function (from pi code). Can anyone help convert the above Raspberry Pi code into C++? It will be greatly appreciated! Thank You
JR

Hello,
I’m looking to do this exact some thing (use SPI between a Pi and an Arduino). But something might’ve happened to this post. The Arduino code seems to have gone missing from this post. If someone could repost this, I’d appreciate it.
Jmg

How to convert hello word to the uint8_t . I’m planning to mod spidev_test to send data in argument
pischky

Just have got it running on an AlaMode Board from wyolum. One note:
Pull the SS input (Arduino Pin 10) input down to ground by some jumper.
- Gregory
  
  How did you get to the conclusion? What happens if you don’t?
  Thank you
  - pischky
    
    The transfer does not work. May be you have luck sometimes and the input is floating to ground. Better than pulling SS to ground is using one extra level shifter from Pi pins CS0 or CS1. Level shifter for other pins are includes on AlaMode Board.
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MatUtter

Thank you so much for being the only in depth article online!

I’ve follow this article to the T.

I’t works great, the SS held high triggers the Arduino’s interrupt but there is a problem with the data.

The data is only ever 0x0, my stomach is telling me its an issue with the Pi.

Any idea what the issue could be? Bad sync? Not transmitting data correctly?

Also, is there any reason to use a logic level converter between these? (I have a bunch of these laying around http://www.mdfly.com/products/logic-level-converter-2-5v-3-3v-5v.html )
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kevenlaker

You may need $11.9 Arduino shield CANBUS here: http://www.elecfreaks.com/store/canbus-shield-p-746.html
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AndiSh

PROTECT your 3,3V I/O Pins on Raspi… at least with 5kOhms…
(+ live coding with Mathematica/Wolfram)

Hello,
please, if you don’t have anything else available, at least introduce series resistors.
This limits the current when accidentally “Out LOW” meets “Out HIGH” or Out5V meets In3.3V.
Current on input shall not exceed 1mA. Makes 5kOhms. OK, 4,7kOhm. Works, if no real fast signals or Pull up/downs or bad EMI-noisy environments are involved.

The bus transceiver does a 3,3V job in both directions. So the 5V device has to cope with a HIGH signal of 3.3V.
If the switching hysteresis of the 5V device are OK with this, it is a no-delay fast bidirectional (without having to set direction, has no input for this) thingy to use, more stable than the auto-magic bidirectional true level-shifters also available, which might oszillate when wires are to long or PCB design is not really HF-reflection-proof; and to admit, my lousy breadboard without ground plane underneath, well, did not have the mony for the 3M breadboard… 😉

(Only the cmos specs state 0,3*VCC and 0,7*VCC for LOW and HIGH. Thats not quite achieved…)
Why not let arduino run at 3,8V ? Would mitigate things 😉 (Tip I read: best _not_ to translate, meaning not having to translate 😉

Good luck!

(We can not run on 5V till end of days, so I sighed and bougt a due and a raspi, no conversion problem; still this is seemingly a contradiction, both beeing 32bit bla… but I want to program Arduino from Mathematica / Wolfram.

Then Mathworks can be the frontend for a digital/analog workbench, with full force analysis (and synthesis) at hand. http://www.wolfram.com/raspberry-pi/?source=footer
and
https://reference.wolfram.com/language/ref/device/Arduino.html
where they explain how arduino is controlled via serial, but also gets a new c++ program uploaded when the changes in wolfram demand it.
Should ask them if it could be done via debugging mode code insertion ;))
Still don’t know if DUE is supportet. Maybe not yet.
(Matlab/Simulink have this in their classroom licence for schools, it is part of their product named “coder”. Supporting coding for Raspi, Arduino, Lego Mindstorms EV3. It uploads code, afterwards target system runs the program, if wanted, autonomously or with communication.
What’s missing for me is cpld and the analog programming cypress pSoC4.. offers, but with more cells, at least a few k.)
Fred

May you help me?
Have you used wiringPi?

I am trying to establish a connection between both arduino and raspberry, but i only get garbage.

So I have some questions:

1) Where is the Slave Select pin?
2) Can I turn the Arduino using only the SPI?
3) How to I set the comunication speed on arduino?
4) Why do I only get garbage?

Here is my Raspberry code:

#include // printf()
#include // signal()
#include // strerro
#include

#include // GPIO
#include // SPI

int volatile interrupt = 0;
#define len_max 100
int volatile len = 0;
unsigned char buffer[len_max];
static const int speed = 500000;

int const CE0 = 0;

void sig_handler(int signo)
{
if(signo == SIGINT)
{
interrupt = 1;
}
}

void setup(void)
{
signal(SIGINT, sig_handler);

wiringPiSetupGpio () ;

if(wiringPiSPISetup(CE0, speed) < 0)
{
printf("SPI setup failed: %s\n", strerror(errno));
interrupt = 1;
}

printf("System ready.\n");
}

void loop(void)
{
memcpy(buffer, "Hello world!\n", sizeof buffer);
len = 12;
if( wiringPiSPIDataRW (CE0, buffer, len) < 0)
printf("Error while recieving mesage\n");
printf("Received mesage: %s \n", buffer);
delay(1000);
}

void close(void)
{
printf("Ending activities.\n");
}

int main(void)
{
setup();
while(!interrupt) loop();
close();
return 0;
}

Please help.
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Coşkun

Guys can you give an example for python?
Susheel Selvamani

how to install the mentioned drivers and modules?
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Horamberg

Not this manga. I meant other ones haha
Xi.DAOFI.CASH/Xc5708R
MEDEVAC343

Tf happening it’s like a roller coaster
vm.DH5WZ4E.CYOUCr5708s

Raspberry Pi + Arduino + SPI

Requirements

Wiring

Arduino

Arduino code

Raspberry Pi

Raspberry Pi Code

Running

Debugging

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