How to execute command by plugging arduino to USB - arduino

Question

The idea is:
Connect arduino to PC via USB port (Windows 7, administrator logged
in)
System automatically execute command (for example: shutdown -s
-t 3600)
Is it possible to make that without using proxy application on host?

Answer 1

Here are two code snippets that address the fundamentals of this question. First, is a sketch that issues a "DIR" command. Obviously, this could be any command.
#include <stdio.h>
uint8_t command[] = "dir\0";
void setup()
{
Serial.begin(9600);
delay(10000);
Serial.write(command, 4);
}
void loop() {}
Second, is C code that reads COM5 and after receiving a string issues a command.
/*
* main.c
*
* Created on: Sep 29, 2013
* Author: Jack Coleman
*
* This software is for demonstration purposes only.
*
*/
#include <stdio.h>
#include <Windows.h>
//
// create a console that accepts data
// from a com port and issues it as system commands.
//
void display_config(COMMCONFIG *config_comm)
{
printf("BaudRate = ");
switch (config_comm->dcb.BaudRate)
{
case CBR_9600 : printf("9600\n");
}
printf("Parity = %d\n", config_comm->dcb.Parity);
printf("StopBits = %d\n", config_comm->dcb.StopBits);
printf("ByteSize = %d\n", config_comm->dcb.ByteSize);
fflush(stdout);
}
main() // Version 0
{
HANDLE hCOM5;
int config_size;
COMMCONFIG config_comm;
int retc;
int nr_read;
char *comm_char;
char sysline[271];
hCOM5 = CreateFile("COM5", GENERIC_READ, 0, 0,
OPEN_EXISTING, 0, NULL);
if (hCOM5 <= 0)
{
printf("unable to open COM5");
return;
}
GetCommConfig(hCOM5, &config_comm, &config_size);
config_comm.dcb.BaudRate = CBR_9600;
config_comm.dcb.Parity = NOPARITY;
config_comm.dcb.StopBits = ONESTOPBIT;
config_comm.dcb.ByteSize = 8;
retc = SetCommConfig(hCOM5, &config_comm, config_size);
if (retc == 0)
{
printf("SetCommConfig failed.\n");
return;
}
display_config(&config_comm);
// wait here for a possible, initial
// series of 0xFF.
comm_char = sysline;
do
{
ReadFile(hCOM5, comm_char, 1, &nr_read, NULL);
printf("%x nr_read = %d\n", *comm_char, nr_read);
fflush(stdout);
} while (nr_read == 0);
while (nr_read == 1)
{
if (*comm_char == 0x00)
{
printf("%s\n", &sysline[0]);
fflush(stdout);
system(&sysline[0]);
break;
} else {
comm_char++;
}
ReadFile(hCOM5, comm_char, 1, &nr_read, NULL);
printf("%02x\n", *comm_char);
fflush(stdout);
}
return;
}
This was a fun little coding problem. Several lessons were learned: 1) when communicating via a serial line, the C program will simply wait until the first byte is transmitted by the Arduino. There are no syncing chars to preface the data transmission (that is, if there are any they get stripped out by the system code); 2) It is possible to get zero (0) for the number of bytes read.
Could this be used to use an Arduino to issue a shut down command? Yes, but the program would have to be started (i.e. scheduled) and then it would wait for the Arduino to speak.