Raspberry Pi code for raspcatbot control by Wifi joystick (https://esp32.com/viewtopic.php?f=19&t=14803&p=57338#p57338)

dead-man_button.c

/*
   $ gcc -O6 -Wall -pedantic -Wextra -o dead-man_button dead-man_button.c -lpigpio -lrt -lpthread
   $

   Usage:
   $ sudo killall pigpiod
   $ sudo ./dead-man_button
   $
*/
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <unistd.h>
#include <stdint.h>
#include <assert.h>
#include <sys/types.h> 
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/select.h>

#include <pigpio.h>

#define gpioLeftFwd 25 // 27
#define gpioLeftRew  9 // 22
#define gpioLeftPwm 24 // 23
#define gpioRghtFwd 23 // 25
#define gpioRghtRew 17 //  9
#define gpioRghtPwm 18 // 10

int sockfd, nfd;

void emergency_stop(int loc)
{
  // simple version; later "high speed small area"
  fprintf(stderr, "emergency stop (%d)\n", loc);
  gpioWrite(gpioLeftFwd, 0);
  gpioWrite(gpioLeftRew, 0);
  gpioPWM(gpioLeftPwm, 0);
  gpioWrite(gpioRghtFwd, 0);
  gpioWrite(gpioRghtRew, 0);
  gpioPWM(gpioRghtPwm, 0);
  gpioTerminate();
  close(nfd);
  close(sockfd);
  exit(1);
}

int main(int argc, char *argv[])
{
  uint8_t buf[8];
  fd_set set;
  socklen_t clilen;
  struct sockaddr_in serv_addr, cli_addr;
  int port = (argc>1) ? atoi(argv[1]) : 1337;

  assert(gpioInitialise()>=0);

  gpioSetMode(gpioLeftFwd, PI_OUTPUT);
  gpioSetMode(gpioLeftRew, PI_OUTPUT);
  gpioSetMode(gpioRghtFwd, PI_OUTPUT);
  gpioSetMode(gpioRghtRew, PI_OUTPUT);

  gpioWrite(gpioLeftFwd, 0);
  gpioWrite(gpioLeftRew, 0);
  gpioPWM(gpioLeftPwm, 0);
  gpioWrite(gpioRghtFwd, 0);
  gpioWrite(gpioRghtRew, 0);
  gpioPWM(gpioRghtPwm, 0);

  assert( (sockfd = socket(AF_INET, SOCK_STREAM, 0) ) >= 0);
  bzero((char *) &serv_addr, sizeof(serv_addr));
  serv_addr.sin_family = AF_INET;
  serv_addr.sin_addr.s_addr = INADDR_ANY;
  serv_addr.sin_port = htons(port);
  assert( bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) >= 0);
  listen(sockfd,5);
  clilen = sizeof(cli_addr);
  nfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen);
  assert(nfd >= 0); 

  FD_ZERO(&set); FD_SET(nfd, &set);

  read(nfd, buf, 1);

  bzero((char *) buf, sizeof(buf));

  while (1)
  {
//    fprintf(stderr, ".");
    struct timeval timeout1={.tv_sec=0, .tv_usec=500000};
    if (select(nfd + 1, &set, NULL, NULL, &timeout1) <= 0)  emergency_stop(1);
    if (read(nfd, buf, 1 ) < 1)  emergency_stop(2);
    struct timeval timeout2={.tv_sec=0, .tv_usec=500000};
    if (select(nfd + 1, &set, NULL, NULL, &timeout2) <= 0)  emergency_stop(3);
    if (read(nfd, buf+4, 1 ) < 1)  emergency_stop(4);  

    gpioWrite(gpioLeftFwd, buf[4] >= 112);
    gpioWrite(gpioLeftRew, buf[4] < 112);
    gpioWrite(gpioRghtFwd, buf[0] >= 112);
    gpioWrite(gpioRghtRew, buf[0] < 112);
    gpioPWM(gpioLeftPwm, (buf[4] < 112) ? 255-(255/112.0)*buf[4] : (255/143.0)*buf[4]-255);
    gpioPWM(gpioRghtPwm, (buf[0] < 112) ? 255-(255/112.0)*buf[0] : (255/143.0)*buf[0]-255);
  }

  gpioTerminate();

  return 0;
}