Hi Khoa Le,
As I understand, you're wishing to transmit from BBB (BBB as Master device),
and receive at the Arduino (Slave).
If you're using a 5V logic level Arduino (e.g. Arduino Uno) then make sure to
keep the MISO pin on both BBB and Arduino disconnected.
The only pins that should be connected should be MOSI to MOSI, and similarly
CLK to CLK, and CS to CS and GND to GND.
Is that how you've got it connected?
Also, this code needs changing I think:
buf [pos++] = c;
Serial.println(buf[pos],HEX);
The pos variable is incremented on the first line, but the second line is
trying to print the contents of the array index after it has been incremented.
Best to put pos=pos++; on a separate line, so you can print before it is
incremented.
Finally, (there may be other bugs too but I am not sure), although it may not
be completely necessary here, generally a logic analyzer can help, and they are
low-cost (search for 'salae logic' or a clone (there are open source and open
hardware versions which are compatible), sometimes just $10 or so. With that,
it is quick to narrow down which side the issue is on, i.e. if the BBB is
transmitting correctly or not. But in this case it's likely not needed if your
BBB test was successful (I don't know what that spidev_test.c is supposed to
output).
Thanks,
Shabaz.
________________________________
From: [email protected] <[email protected]> on behalf of
Khoa Le <[email protected]>
Sent: 12 April 2020 01:28
To: BeagleBoard <[email protected]>
Subject: [beagleboard] SPI connection between Beaglebone black and Arduino Uno
Hello All,
I just started to use BBB a couple days. My goal is trying to test the
connection between the BBB and the Arduino over SPI.
I did some research on the internet and and borrow some of the code just to see
if the result is the same as I expect.
1) I make sure the SPI pins of the BBB is working by using the
spidev_test.c<https://raw.githubusercontent.com/raspberrypi/linux/rpi-3.10.y/Documentation/spi/spidev_test.c>
and the result as below:
sedf
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0x40, 0x00, 0x00, 0x00, 0x00, 0x95,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xDE, 0xAD, 0xBE, 0xEF, 0xBA, 0xAD,
0xF0, 0x0D,
2) So, I tried to send to the Arduino some bytes and expected that the Arduino
would show the result on the Serial Monitor. However, the Aruino seems not to
get the correct the message.
I'm not sure the voltage difference between Arduino and BBB has anything to do
with this.
Please see the code for the BBB and The BBB below:
Arduino: I looked at Nick Gammon blog and started to follow his example to make
Arduino as slave
//this code is written by by Nick Gammon
#include <SPI.h>
char buf [100];
volatile byte pos;
volatile boolean process_it;
void setup (void)
{
Serial.begin (9600); // 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 = 0;
// now turn on interrupts
SPI.attachInterrupt();
} // end of setup
// SPI interrupt routine
ISR (SPI_STC_vect)
{
char c = SPDR; // grab byte from SPI Data Register
// add to buffer if room
if (pos < sizeof buf)
{
buf [pos++] = c;
Serial.println(buf[pos],HEX);
// example: newline means time to process buffer
if (c == 0x04)
process_it = 1;
} // 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 == 1)
{
buf [pos] = 0;
Serial.println("SPI");
Serial.println (buf);
pos = 0;
process_it = 0;
} // end of flag set
} // end of loop
and BBB:
#include <stdint.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <stdlib.h>
#include <linux/types.h>
#include <sys/ioctl.h>
#include <linux/spi/spidev.h>
//define some constant variables
#define PATH "/dev/spidev2.0"
static uint16_t delay =0;
static uint32_t speed = 100000;
static uint8_t bits = 8;
static uint8_t mode = 0;
#define ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))
void write_data(int fd){
int ret;
char tx[]= {0x08,0x01,0x04};
char 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<0){
perror("SPI_IOC_MESSAGE");
}
}
int main(void) {
int ret,fd;
fd = open(PATH,O_RDWR);
if (fd<0){
perror("Bad fd open - check PATH");}
//setup SPI mode
ret = ioctl(fd,SPI_IOC_WR_MODE,&mode);
if(ret<0){
perror("SPI_IOC_WR_MODE");}
ret = ioctl(fd,SPI_IOC_RD_MODE,&mode);
if(ret<0){
perror("SPI_IOC_RD_MODE");}
ret = ioctl(fd,SPI_IOC_WR_BITS_PER_WORD,&bits);
if(ret<0){
perror("SPI_IOC_WR_BITS_PER_WORD");}
ret = ioctl(fd,SPI_IOC_RD_BITS_PER_WORD,&bits);
if(ret<0){
perror("SPI_IOC_RD_BITS_PER_WORD");}
ret = ioctl(fd,SPI_IOC_WR_MAX_SPEED_HZ,&speed);
if(ret<0){
perror("SPI_IOC_WR_MAX_SPEED_HZ");}
ret = ioctl(fd,SPI_IOC_RD_MAX_SPEED_HZ,&speed);
if(ret<0){
perror("SPI_IOC_RD_MAX_SPEED_HZ");}
write_data(fd); // send data
usleep(100*1000);
close(fd);
return 0;
}
Any comment/suggestion/answer would help. If I write anything wrong, please
feel free to point it out.
Also, this is first time I ask question online and join a forum.
Thank you.
Khoa
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