[SOLVED] UDP send

lokal1 · 08-07-2021, 11:32 AM

Hi,
Newbie here, the only knowledge I have is from googling.
Please bear with me.

How does one properly send data over UDP?
I have a data like this:

Code:

typedef union {
    struct {
        uint8_t buffer[BUFF_SIZE]; // 64
    } tx;

    struct {
        int32_t header;
        volatile int32_t Cmd[COMMAND_SIZE]; // 4
        float setPoint[VARIABLES]; // 6
        uint8_t enable;
        uint8_t outputs;
        uint8_t spar0;
        uint8_t spar1;
    } data;

} txData_t;

txData_t txData;

The header is always a fixed data.
Only header and enable has initial value greater than 0,
the rest are 0 values.
I'm sending the whole 64byte buffer over UDP, but I'm only receiving
the header, I'm expecting to also receive the enable value
but it's not there.
What do I need to do to make sure I receive the datas or for that matter
how do I make sure that the datas are actually getting sent.

NevemTeve · 08-07-2021, 12:06 PM

Guess your code looks like this:

Code:

txData *ptr;
struct sockaddr_in partner;
...
sendto (socket, ptr, sizeof ptr, (struct sockaddr *)&partner, sizeof partner);

Suggested fix:

Code:

sendto (socket, ptr, sizeof *ptr, (struct sockaddr *)&partner, sizeof partner);

PS: or similiar change with `recv`: instead of `sizeof pointer` use `sizeof *pointer` or `BUFF_SIZE`

lokal1 · 08-07-2021, 12:59 PM

Hi thanks,

I'm actually using just send.

Code:

udpSocket = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
...
bzero((char*) &server_addr, sizeof(server_addr));
server_addr.sin_family = AF_INET; // IPv4
server_addr.sin_port = htons(UDP_PORT);
server_addr.sin_addr.s_addr = inet_addr(remoteAddress);

/* Connect to send and receive only to the server_addr */
ret = connect(udpSocket, (struct sockaddr*) &server_addr,
      sizeof(struct sockaddr_in));

//setup timeouts
...

// then send.
ret = send(udpSocket, txData.tx.buffer, BUFF_SIZE, 0);
...

ret = recv(udpSocket, rxData.rx.buffer, BUFF_SIZE, 0);
...

NevemTeve · 08-07-2021, 04:07 PM

Do you have a rxData_t type?

lokal1 · 08-07-2021, 05:14 PM

yes, I just didn't post it.
rxData is a different type/stucture
It belongs to the same code as txData on
the client side.

The other side, the server, where I receive is identical
typedef'ed union as the txData, but named rxData
since its the receiver.

Edit:
Ok maybe it's a bit confusing.

both sides has txData/rxData with identical structure
except it's name is the reverse. The structure of txData on the
client side is identical to server, just on the server side
it's named rxData. Same with the others.

NevemTeve · 08-07-2021, 11:54 PM

I think it would be the right time to read this:
https://stackoverflow.com/help/minim...ucible-example

lokal1 · 08-08-2021, 05:23 AM

Thanks for the patience.
This is basically it. My recieving end is similar.

Code:

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>

#define COMMAND_SIZE   4
#define VARIABLES      6
#define BUFF_SIZE      64

#define UDP_PORT        20218
#define SEND_TIMEOUT_US 1000
#define RECV_TIMEOUT_US 1000

static const char *remoteAddress = "127.0.0.1";

typedef union {
    struct {
        uint8_t buffer[BUFF_SIZE];
    } tx;

    struct {
        int32_t header;
        int32_t Cmd[COMMAND_SIZE];
        float setPoint[VARIABLES];
        uint8_t enable;
        uint8_t outputs;
        uint8_t spar0;
        uint8_t spar1;
    } data;

} txData_t;


typedef union {
    struct {
        uint8_t buffer[BUFF_SIZE];
    } rx;

    struct {
        int32_t header;
        int32_t Feedback[COMMAND_SIZE];   
        float processVariable[VARIABLES]; 
        uint8_t inputs;
    } data;

} rxData_t;


rxData_t rxData;
txData_t txData;


int main() {
  int ret;
  int udpSocket;
  struct sockaddr_in server_addr;

  udpSocket = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
  if (udpSocket < 0) {
    printf("ERROR: can't open socket: %s\n", strerror(errno));
    return -errno;
  }

  bzero((char*) &server_addr, sizeof(server_addr));
  server_addr.sin_family = AF_INET; // IPv4
  server_addr.sin_port = htons(UDP_PORT);
  server_addr.sin_addr.s_addr = inet_addr(remoteAddress);

  /* Connect to send and receive only to the server_addr */
  ret = connect(udpSocket, (struct sockaddr*) &server_addr,
      sizeof(struct sockaddr_in));

  if (ret < 0) {
    printf("ERROR: can't connect: %s\n", strerror(errno));
    return -errno;
  }

  struct timeval timeout;
  timeout.tv_sec = 0;
  timeout.tv_usec = RECV_TIMEOUT_US;

  ret = setsockopt(udpSocket, SOL_SOCKET, SO_RCVTIMEO, (char*) &timeout,
      sizeof(timeout));
  if (ret < 0) {
    printf("ERROR: can't set receive timeout socket option: %s\n",
        strerror(errno));
    return -errno;
  }

  timeout.tv_usec = SEND_TIMEOUT_US;
  ret = setsockopt(udpSocket, SOL_SOCKET, SO_SNDTIMEO, (char*) &timeout,
      sizeof(timeout));
  if (ret < 0) {
    printf("ERROR: can't set send timeout socket option: %s\n",
        strerror(errno));
    return -errno;
  }
  
  for(int i=0; i<sizeof(txData.tx.buffer); i++) {
  	txData.tx.buffer[i] = 0;
  }
  
	txData.data.header = 0x77726974;
	txData.data.enable = 0x07;

  ret = send(udpSocket, txData.tx.buffer, BUFF_SIZE, 0);
  if (ret < 0) {
    printf("ERROR: Unable to send: %s\n", strerror(errno));
  }else{
  	printf("Data sent %d\n", ret);
  }
/*
  ret = recv(udpSocket, rxData.rx.buffer, BUFF_SIZE, 0);
  if (ret < 0) {
    printf("ERROR: Unable to receive: %s\n", strerror(errno));
  }else{
  	printf("Data received %d\n", ret);
  }
*/ 
  
  close(udpSocket);
}

I have just tested it with a simulated server on my PC,
(the actual server is a microcontroller).
Learnt a bit of wireshark, I just found out that in the
(hex view) packet bytes the value '7' is there. Since it's a not printable
value, it's not in the packet details?
I'll investigate further, if you have more input that would be great.

NevemTeve · 08-08-2021, 10:33 AM

You cannot read the 'enable' field from the 'rxData_t' structure, because it doesn't have such a field. You can find it out if you add more debug-print into your program. Example attached.

smallpond · 08-08-2021, 11:25 AM

You should verify that you receive BUFF_SIZE bytes before looking at the contents.

lokal1 · 08-08-2021, 12:05 PM

Thanks Guys/Gals,

The txData/rxData in the posted code is just for the client.
The server also has the txData/rxData. The rxData union of
the server is identical to the txData of the client same
as the txData of the server is identical to rxData of the client.

I've verified the received bytes. It says 64bytes so
I'm getting all the bytes just not sure why not the correct bytes.
If I'm seeing it in wireshark it's being sent, I'll have a
second look at the receiving end.

Thanks again.

smallpond · 08-08-2021, 01:23 PM

Are both machines the same architecture?

lokal1 · 08-08-2021, 05:42 PM

'figured it out. I wasn't clearing the DMA transfer complete flag.
The client is a RaspberryPi, talking to an STM32F4.
I believe the Rpi can do both endian, but the micro is definitely little ender.

Thanks guys.or gals.

Edit:

How does one make this thread solved?

GazL · 08-09-2021, 07:19 AM

Quote:

Originally Posted by lokal1

How does one make this thread solved?

"Thread tools" pull down menu, towards the top of the page.

lokal1 · 08-09-2021, 01:14 PM

Thanks.