how we can send msg from publisher to subscriber on different topics in one structure and how topics can be retrieved in subscriber.
C/C++ code example
Q : "how we can send msg from publisher to subscriber on different topics in one structure...?"
The pub-side can do just sending, like this :
#include <nanomsg/nn.h>
#include <nanomsg/pubsub.h>
...
int pub = nn_socket (AF_SP, NN_PUB);
assert (pub >= 0);
...
int nbytes;
char *addr = "inproc://example";
nn_bind(pub, addr);
...
nbytes = nn_send (pub, "a_Topic_#1abcdefghijklmnopqr", 28);
assert(nbytes == 28);
nbytes = nn_send (pub, "a_Topic_#2abcdefghijklmnopqr", 28);
assert(nbytes == 28);
...
nn_freemsg (buf);
...
Q : "... and how topics can be retrieved in subscriber?"
Using basically this mock-up principle, the sub-side has to subscribe first :
#include <nanomsg/nn.h>
#include <nanomsg/pubsub.h>
...
int sub = nn_socket (AF_SP, NN_SUB);
assert (sub >= 0);
...
int nbytes;
void *buf = NULL;
char *addr = "inproc://example";
nn_connect(sub, addr);
...
nn_setsockopt (sub, NN_SUB, NN_SUB_SUBSCRIBE, "a_Topic_#1", 10);
nn_setsockopt (sub, NN_SUB, NN_SUB_SUBSCRIBE, "a_Topic_#2", 10);
...
nbytes = nn_recv (sub, &buf, NN_MSG, 0);
assert (nbytes == 28);
nn_freemsg (buf);
...
Related
In child Process when I am writing to pipe 2 after reading data from pipe 1 then after writing no other instruction is being executed. Like if i create another process but the fork system call is not executed. I have also tried by restoring the stdout file descriptor and then cout something but nothing happpens on console..
please have a look. I think there might be some ambiguity in closing the pipes or dup2 which i am unable to get. Thanks.
`#include<iostream>
#include<unistd.h>
#include<fcntl.h>
#include<sys/wait.h>
using namespace std;
int main()
{
char buff[100];
int fd1[2];
int fd2[2];
pipe(fd1);
pipe(fd2);
pid_t pid1 = fork();
if(pid1 > 0)
{
//int a = dup(1);
close(fd1[0]);
close(fd2[0]);
dup2(fd1[1], 1);
cout<<"Hello"<<endl;
//dup2(a,1);
//cout<<"hellow"<<endl;
//dup2(fd2[0], 0);
//cin>>buff;
//cout<<buff<<endl;
close(fd1[1]);
//close(a);
}
else if(pid1 == 0)
{
int a = dup(1);
close(fd1[1]);
close(fd2[0]);
dup2(fd1[0], 0);
cin>>buff;
cout<<buff<<endl;
dup2(fd2[1], 1);
cout<<buff<<endl;
close(fd1[0]);
close(fd2[1]);
pid_t pid2 = fork();
if(pid2 == 0)
{
cout<<"In C2 "<<endl;
}
}
return 0;
}
First off all I am a beginner regarding embedded programming.
For an application I do want to use the MLX90621 thermo pixel array togehter with an STM32G431KB. On the Melexis Website is an example Code with some sort off abstraction. I moddified the lowlevel part of the code to work with the HAL library of the MCU.
For some reason I can read the EEPROM and write to it, get an acknowledge... But when trying to read from the adress 0x60, the RAM, where the sensorvalues are stored i do not get an acknowledge. I do have checkt with an logic analyer and I am sending the correct messages. Just for refference I do have added the code part of the read function.
Has anybody an idea regarding some very dump timing error or something like that.
P.S. Allready tried an different sensor of my order with the exact same result.
int MLX90621_I2CRead(uint8_t slaveAddr,uint8_t command, uint8_t startAddress, uint8_t addressStep, uint8_t nMemAddressRead, uint16_t *data)
{
uint8_t sa = slaveAddr << 1;
int cnt = 0;
int i = 0;
uint8_t cmd[4] = {0,0,0,0};
uint8_t i2cData[132] = {0};
uint16_t *p;
p = data;
cmd[0] = command;
cmd[1] = startAddress;
cmd[2] = addressStep;
cmd[3] = nMemAddressRead;
if (HAL_I2C_Master_Transmit(&hi2c2, sa, cmd, 4, HAL_MAX_DELAY) != HAL_OK)
return -1;
HAL_Delay(1);
//sa = sa | 0x01;
//ack = i2c.read(sa, i2cData, 2*nMemAddressRead, 0);
if (HAL_I2C_Master_Receive(&hi2c2, sa, i2cData, 2*nMemAddressRead, HAL_MAX_DELAY) != HAL_OK)
return -1;
for (cnt = 0; cnt < nMemAddressRead; cnt++) {
i = cnt << 1;
*p++ = (uint16_t)i2cData[i+1]*256 + (uint16_t)i2cData[i];
}
return 0;
}
I'm looking at the following code from STMicroelectronics on implementing USART communication with interrupts
#include <stm32f10x_lib.h> // STM32F10x Library Definitions
#include <stdio.h>
#include "STM32_Init.h" // STM32 Initialization
/*----------------------------------------------------------------------------
Notes:
The length of the receive and transmit buffers must be a power of 2.
Each buffer has a next_in and a next_out index.
If next_in = next_out, the buffer is empty.
(next_in - next_out) % buffer_size = the number of characters in the buffer.
*----------------------------------------------------------------------------*/
#define TBUF_SIZE 256 /*** Must be a power of 2 (2,4,8,16,32,64,128,256,512,...) ***/
#define RBUF_SIZE 256 /*** Must be a power of 2 (2,4,8,16,32,64,128,256,512,...) ***/
/*----------------------------------------------------------------------------
*----------------------------------------------------------------------------*/
#if TBUF_SIZE < 2
#error TBUF_SIZE is too small. It must be larger than 1.
#elif ((TBUF_SIZE & (TBUF_SIZE-1)) != 0)
#error TBUF_SIZE must be a power of 2.
#endif
#if RBUF_SIZE < 2
#error RBUF_SIZE is too small. It must be larger than 1.
#elif ((RBUF_SIZE & (RBUF_SIZE-1)) != 0)
#error RBUF_SIZE must be a power of 2.
#endif
/*----------------------------------------------------------------------------
*----------------------------------------------------------------------------*/
struct buf_st {
unsigned int in; // Next In Index
unsigned int out; // Next Out Index
char buf [RBUF_SIZE]; // Buffer
};
static struct buf_st rbuf = { 0, 0, };
#define SIO_RBUFLEN ((unsigned short)(rbuf.in - rbuf.out))
static struct buf_st tbuf = { 0, 0, };
#define SIO_TBUFLEN ((unsigned short)(tbuf.in - tbuf.out))
static unsigned int tx_restart = 1; // NZ if TX restart is required
/*----------------------------------------------------------------------------
USART1_IRQHandler
Handles USART1 global interrupt request.
*----------------------------------------------------------------------------*/
void USART1_IRQHandler (void) {
volatile unsigned int IIR;
struct buf_st *p;
IIR = USART1->SR;
if (IIR & USART_FLAG_RXNE) { // read interrupt
USART1->SR &= ~USART_FLAG_RXNE; // clear interrupt
p = &rbuf;
if (((p->in - p->out) & ~(RBUF_SIZE-1)) == 0) {
p->buf [p->in & (RBUF_SIZE-1)] = (USART1->DR & 0x1FF);
p->in++;
}
}
if (IIR & USART_FLAG_TXE) {
USART1->SR &= ~USART_FLAG_TXE; // clear interrupt
p = &tbuf;
if (p->in != p->out) {
USART1->DR = (p->buf [p->out & (TBUF_SIZE-1)] & 0x1FF);
p->out++;
tx_restart = 0;
}
else {
tx_restart = 1;
USART1->CR1 &= ~USART_FLAG_TXE; // disable TX interrupt if nothing to send
}
}
}
/*------------------------------------------------------------------------------
buffer_Init
initialize the buffers
*------------------------------------------------------------------------------*/
void buffer_Init (void) {
tbuf.in = 0; // Clear com buffer indexes
tbuf.out = 0;
tx_restart = 1;
rbuf.in = 0;
rbuf.out = 0;
}
/*------------------------------------------------------------------------------
SenChar
transmit a character
*------------------------------------------------------------------------------*/
int SendChar (int c) {
struct buf_st *p = &tbuf;
// If the buffer is full, return an error value
if (SIO_TBUFLEN >= TBUF_SIZE)
return (-1);
p->buf [p->in & (TBUF_SIZE - 1)] = c; // Add data to the transmit buffer.
p->in++;
if (tx_restart) { // If transmit interrupt is disabled, enable it
tx_restart = 0;
USART1->CR1 |= USART_FLAG_TXE; // enable TX interrupt
}
return (0);
}
/*------------------------------------------------------------------------------
GetKey
receive a character
*------------------------------------------------------------------------------*/
int GetKey (void) {
struct buf_st *p = &rbuf;
if (SIO_RBUFLEN == 0)
return (-1);
return (p->buf [(p->out++) & (RBUF_SIZE - 1)]);
}
/*----------------------------------------------------------------------------
MAIN function
*----------------------------------------------------------------------------*/
int main (void) {
buffer_Init(); // init RX / TX buffers
stm32_Init (); // STM32 setup
printf ("Interrupt driven Serial I/O Example\r\n\r\n");
while (1) { // Loop forever
unsigned char c;
printf ("Press a key. ");
c = getchar ();
printf ("\r\n");
printf ("You pressed '%c'.\r\n\r\n", c);
} // end while
} // end main
My questions are the following:
In the handler function, when does the statement ((p->in - p->out) & ~(RBUF_SIZE-1)) ever evaluate to a value other than zero? If RBUF_SIZE is a power of 2 as indicated, then ~(RBUF_SIZE-1) should always be zero. Is it checking if p->in > p->out? Even if this isn't true, the conditional should evaluate to zero anyway, right?
In the line following, the statement p->buf [p->in & (RBUF_SIZE-1)] = (USART1->DR & 0x1FF); is made. Why does the code AND p->in with RBUF_SIZE-1?
What kind of buffer are we using in this code? FIFO?
Not so. For example, assuming 32-bit arithmetic, if RBUF_SIZE == 0x00000100 then RBUF_SIZE-1 == 0x000000FF and ~(RBUF_SIZE-1) == 0xFFFFFF00 (it's a bitwise NOT, not a logical NOT). The check you refer to is therefore effectively the same as (p->in - p->out) < RBUF_SIZE, and it's not clear why it is superior. ARM GCC 7.2.1 produces identical length code for the two (-O1).
p->in & (RBUF_SIZE-1) is the same as p->in % RBUF_SIZE when p->in is unsigned. Again, not sure why the former would be used when the latter is clearer; sure, it effectively forces the compiler to compute the modulo using an AND operation, but given that RBUF_SIZE is known at compile time to be a power of two my guess is that most compilers could figure this out (again, ARM GCC 7.2.1 certainly can, I've just tried it - it produces the same instructions either way).
Looks like it. FIFO implemented as a circular buffer.
Following codes demonstrate shared memory between two process (server & client )
This code transfer characters between two program , but i want to transfer NSData between two programs within this code
How can I do this?
shm_server.c
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdio.h>
#define SHMSZ 27
int main()
{
char c;
int shmid;
key_t key;
char *shm, *s;
/*
* We'll name our shared memory segment
* "5678".
*/
key = 5678;
/*
* Create the segment.
*/
if ((shmid = shmget(key, SHMSZ, IPC_CREAT | 0666)) < 0) {
perror("shmget");
exit(1);
}
/*
* Now we attach the segment to our data space.
*/
if ((shm = shmat(shmid, NULL, 0)) == (char *) -1) {
perror("shmat");
exit(1);
}
/*
* Now put some things into the memory for the
* other process to read.
*/
s = shm;
for (c = 'a'; c <= 'z'; c++)
*s++ = c;
*s = NULL;
/*
* Finally, we wait until the other process
* changes the first character of our memory
* to '*', indicating that it has read what
* we put there.
*/
while (*shm != '*')
sleep(1);
exit(0);
}
shm_client.c
/*
* shm-client - client program to demonstrate shared memory.
*/
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdio.h>
#define SHMSZ 27
int main()
{
int shmid;
key_t key;
char *shm, *s;
/*
* We need to get the segment named
* "5678", created by the server.
*/
key = 5678;
/*
* Locate the segment.
*/
if ((shmid = shmget(key, SHMSZ, 0666)) < 0) {
perror("shmget");
exit(1);
}
/*
* Now we attach the segment to our data space.
*/
if ((shm = shmat(shmid, NULL, 0)) == (char *) -1) {
perror("shmat");
exit(1);
}
/*
* Now read what the server put in the memory.
*/
for (s = shm; *s != NULL; s++)
putchar(*s);
putchar('\n');
/*
* Finally, change the first character of the
* segment to '*', indicating we have read
* the segment.
*/
*shm = '*';
exit(0);
}
Thanks in advance
Better to use Distributed Objects.
You need to serialize your data, put it in the shared memory, then de-serialize, just like you would if you sent data over a network. This example is a bit in-efficient in that it serialises to a text format, but it should work well enough.
I am trying to get the ARP entries on my iPad like here.
When compiling the code to run on my iPad (so not the simulator) I am getting missing header error messages. You can resolve them by copying the header files into you project locally as mentioned in this post.
The problem lies in the line
sdl = (struct sockaddr_dl *)(sin + 1);
in this piece of code:
-(NSString*) ip2mac: (char*) ip
{
int expire_time, flags, export_only, doing_proxy, found_entry;
NSString *mAddr = nil;
u_long addr = inet_addr(ip);
int mib[6];
size_t needed;
char *host, *lim, *buf, *next;
struct rt_msghdr *rtm;
struct sockaddr_inarp *sin;
struct sockaddr_dl *sdl;
extern int h_errno;
struct hostent *hp;
mib[0] = CTL_NET;
mib[1] = PF_ROUTE;
mib[2] = 0;
mib[3] = AF_INET;
mib[4] = NET_RT_FLAGS;
mib[5] = RTF_LLINFO;
if (sysctl(mib, 6, NULL, &needed, NULL, 0) < 0)
err(1, "route-sysctl-estimate");
if ((buf = malloc(needed)) == NULL)
err(1, "malloc");
if (sysctl(mib, 6, buf, &needed, NULL, 0) < 0)
err(1, "actual retrieval of routing table");
lim = buf + needed;
for (next = buf; next < lim; next += rtm->rtm_msglen) {
rtm = (struct rt_msghdr *)next;
sin = (struct sockaddr_inarp *)(rtm + 1);
sdl = (struct sockaddr_dl *)(sin + 1);
if (addr) {
if (addr != sin->sin_addr.s_addr)
continue;
found_entry = 1;
}
if (nflag == 0)
hp = gethostbyaddr((caddr_t)&(sin->sin_addr),
sizeof sin->sin_addr, AF_INET);
else
hp = 0;
if (hp)
host = hp->h_name;
else {
host = "?";
if (h_errno == TRY_AGAIN)
nflag = 1;
}
if (sdl->sdl_alen) {
u_char *cp = LLADDR(sdl);
mAddr = [NSString stringWithFormat:#"%x:%x:%x:%x:%x:%x", cp[0], cp[1], cp[2], cp[3], cp[4], cp[5]];
// ether_print((u_char *)LLADDR(sdl));
}
else
mAddr = nil;
}
if (found_entry == 0) {
return nil;
} else {
return mAddr;
}
}
It gives the following error message:
Arithmetic on pointer to incomplete type 'struct sockaddr_inarp*'
When you compile the code for the iPad simulator everything runs fine.
Does anyone have an idea how to solve this?
A similar question (but not solved) is asked here.
After importing <netinet/if_ether.h>, you should edit it and change the line
#include <net/if_arp.h>
to
#include "if_arp.h"
and then import <net/if_arp.h> in your project as well. This should fix that error.
Anyway the headers you need to import to compile the code you posted are:
#include "if_ether.h"
#include "route.h"
#include "if_arp.h"
#include "if_dl.h"
Hope this helps =)
EDIT:
You need to "Add files to project", not simply importing it with #import or #include.
You can find above files from following links:
Files under "netinet"
Files under "net"
#include <net/ethernet.h>
instead of messing with the original headers. More info here: Implicit declaration of function 'ether_ntoa' is invalid in C99