Experimental Physics and
Industrial Control System

"Mehta, Pratik" <[email protected]> · Thu, 7 May 2009 10:58:15 -0400

Hi,
I have written a libusb code to send strings across to a power meter. I am successfully able to send strings across, but error occurs when I try to read the response from the meter.Can you please tell me am I going wrong?

#include <stdio.h>
#include <usb.h>
#include <time.h>

//clock_t start, end;
//double cpu_time_used;
// int argc, char **argv

int main(int argc, char **argv)
{
        struct usb_bus *busses;

        usb_set_debug(2);

        usb_init();
        usb_find_busses();
        usb_find_devices();

        busses = usb_get_busses();

        struct usb_dev_handle* usb_handle;
        struct usb_bus *bus;
        int c, i, a;

        char buf[255];
        char buf2[5];
        char* ptr = buf;

for (bus = busses; bus; bus = bus->next)
        {
        struct usb_device *dev;

for (dev = bus->devices; dev; dev =dev->next)
                {
/* Check if this device is a power meter */

if (dev->descriptor.idProduct == 0xCEC7)
        {
        int i,stat,j;
                                printf("vendor: %04X\n",dev->descriptor.idVendor);

usb_handle = usb_open(dev);
                                if(usb_handle == NULL) {
                                        printf("Could not open device: %s\n", usb_strerror());
                                }

                                if(usb_handle != NULL) {
                                        printf("<<<Device Open>>>\n");
                                }

                                //usb_detach_kernel_driver_np(usb_handle, 0);

stat = usb_claim_interface(usb_handle,0);
        if(stat ==0){

 printf("Interface Claimed\n");}
                                        //printf ("stat:%d from claim\n",stat);

                buf2[0]='P'; 
                buf2[1]='M';  
                buf2[2]=':'; 
                buf2[3]='P'; 
                buf2[4]='?';
        /*                      buf2[5]=0x38;
                                buf2[6]=0x31;
                                buf2[7]=0x30; */

              i=usb_bulk_write(usb_handle,0x02,buf2, 5, 10);

                                printf("write: %d\n",i);

        for(i=0;i<sizeof(buf2);i++)
        {
                                        printf("buf2[%d]=%X\n",i,buf2[i]);
                                }

 j=usb_bulk_read(usb_handle, 0x81, buf, sizeof(buf), 10);

if(j < 0) {
        printf("No output\n");
        } else
            {                
                                        printf("read %d bytes\n", j);
        }
                                   usb_close(usb_handle);
                        }
                }
        }
        return 0;
}

/////OUTPUT////

pratik-mehtas-macbook-2:~ pratik$ gcc exp4.c -lusb
pratik-mehtas-macbook-2:~ pratik$ ./a.out
usb_set_debug: Setting debugging level to 2 (on)
vendor: 104D
<<<Device Open>>>
libusb/darwin.c get_endpoints: building table of endpoints.
get_endpoints: Pipe 1: DIR: 1 number: 1
get_endpoints: Pipe 2: DIR: 0 number: 2
libusb/darwin.c get_endpoints: complete.
Interface Claimed
libusb/darwin.c ep_to_pipeRef: Converting ep address to pipeRef.
libusb/darwin.c usb_bulk_transfer: Transfering 5 bytes of data on endpoint 0x02
write: 5
buf2[0]=50
buf2[1]=4D
buf2[2]=3A
buf2[3]=50
buf2[4]=3F
libusb/darwin.c ep_to_pipeRef: Converting ep address to pipeRef.
libusb/darwin.c usb_bulk_transfer: Transfering 255 bytes of data on endpoint 0x81
USB error: libusb/darwin.c usb_bulk_transfer: transaction timed out
USB error: usb_bulk_read: An error occured during read (see messages above)
No output
pratik-mehtas-macbook-2:~ pratik$

Thank you,
Pratik Mehta

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System