[libhid-discuss] python works but not C

[Will Woods]

I am successfully talking to my device via the python bindings, but my C
version fails with error 21 "could not claim interface 0: Device or
resource busy" after successfully opening the device. The two pieces of
code look the same to me, but I must be missing something?

Any advice would be much appreciated...


Python code:

import sys
from struct import unpack
from hid import *


ret = hid_init()
if ret != HID_RET_SUCCESS:
    sys.stderr.write("hid_init failed with return code %d.n" % ret)

hid = hid_new_HIDInterface()
if hid == 0:
    sys.stderr.write("hid_new_HIDInterface failed.")

matcher = HIDInterfaceMatcher()
matcher.vendor_id = 0x0488
matcher.product_id = 0x0020

ret = hid_force_open(hid, 0, matcher, 3)
if ret != HID_RET_SUCCESS:
    sys.stderr.write("hid_force_open failed with return code %d.n" % ret)

while True:
    ret, bytes = hid_interrupt_read(hid, 0x81, 8, 100)
    if ret == 0:
        a = unpack('Q',bytes)[0]
        print a






and the C version:


#include <stdio.h>
#include <hid.h>

#define VENDOR_ID 0x0488
#define PRODUCT_ID 0x0020


int main(int argc, char *argv[])
{
    unsigned char bytes[8];

    HIDInterface* hid;
    int iface_num = 0;
    hid_return ret;

    HIDInterfaceMatcher matcher = { VENDOR_ID, PRODUCT_ID, NULL, NULL, 0 };

    // see include/debug.h for possible values
    hid_set_debug(HID_DEBUG_ALL);
    hid_set_debug_stream(stderr);
    // passed directly to libusb
    hid_set_usb_debug(0);

    ret = hid_init();
    if (ret != HID_RET_SUCCESS) {
        fprintf(stderr, "hid_init failed with return code %d\n", ret);
        return 1;
    }

    hid = hid_new_HIDInterface();
    if (hid == 0) {
        fprintf(stderr, "hid_new_HIDInterface() failed, out of memory?\n");
        return 1;
    }

    ret = hid_force_open(hid, iface_num, &matcher, 3);
    if (ret != HID_RET_SUCCESS) {
        fprintf(stderr, "hid_force_open failed with return code %d\n", ret);
        return 1;
    }

    while( 1)
    {
        ret = hid_interrupt_read( hid, 0x81, bytes, 8, 100);

        printf( "ret=%d\n", ret);
        if( ret == HID_RET_SUCCESS )
        {
            // do something
        }

    }

    ret = hid_close(hid);
    if (ret != HID_RET_SUCCESS) {
        fprintf(stderr, "hid_close failed with return code %d\n", ret);
        return 1;
    }

    hid_delete_HIDInterface(&hid);

    ret = hid_cleanup();
    if (ret != HID_RET_SUCCESS) {
        fprintf(stderr, "hid_cleanup failed with return code %d\n", ret);
        return 1;
    }

    return 0;
}