Hi Shabaz,
Thank you for your response. Yes, I'm thinking that I might need a logic
analyzer to see what I send and what I receive.
I manage to send the correct data from tx [] to Arduino with correct order.
As I understand the SPI_IOC_MESSAGE is full-duplex so I also receive the
response from the Arduino back to the BBB as well. However, one thing is
weird is that BBB always receives the last byte first. For example, if tx
[] = {0x08, 0x01, 0x02, 0x04}, what I receive is rx [] = {0x04, 0x08,
0x01,0x02}. Everything else after the last byte seems to be normal.
On the other hand, If I just use half duplex with read() only, I receive
the correct order of what Arduino sends to BBB using SPI.transfer() (from
Arduino).
Thank you.
Khoa Le.
On Mon, Apr 13, 2020 at 10:10 AM Shabaz Yousaf <[email protected]>
wrote:
> Sorry, typo, I meant
> Best to put *pos++;* on a separate line.
>
> ------------------------------
> *From:* [email protected] <[email protected]> on
> behalf of Shabaz Yousaf <[email protected]>
> *Sent:* 13 April 2020 14:57
> *To:* BeagleBoard <[email protected]>
> *Subject:* Re: [beagleboard] SPI connection between Beaglebone black and
> Arduino Uno
>
> 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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