Hi all,
I am using GET_DEVICE_ID request sepcified in <USB Device class Definition for
Printing Devices> to get the printer's description.
I use usb_control_msg to get the id-string. But something just does strange.
I use HP DeskJet 1125C to do the test, when first pluged(USB), run the test
program, it just return null string. And run again the test program, it show the
correct id-string.
And if pulled out and pluged again, run the program first, it will show NULL
string again, and the second time it shows correct.
If change the printer to Epson, the problem not exist.
Is this the problem the HP printer has, or my test program?
Please give me some advice, thanks in advance!
Follwing is my test program:
#include <usb.h>
#include <stdio.h>
#include <stdlib.h>
int main()
{
struct usb_device* dev;
struct usb_bus* bus;
usb_init();
usb_find_busses();
usb_find_devices();
bus = usb_get_busses();
for (; bus; bus = bus->next)
{
for (dev = bus->devices; dev; dev=dev->next)
{
if (dev->config->interface->num_altsetting == 3) //find hp printer, only hp printer
has 3 altsetting in test
{
//begin to get device id
usb_dev_handle* dev_handle;
dev_handle = usb_open(dev);
usb_claim_interface(dev_handle, 0);
char deviceid[256] = {0};
usb_control_msg(dev_handle, 0xA1, 0, 0, 0, deviceid, 256, 50000);
int i;
for (i = 0; i < 256; i++)
printf("%c", deviceid[i]); //first show nothing , second and later show correct
id string
printf("\n");
usb_release_interface(dev_handle, 0);
usb_close(dev_handle);
return 0;
}
}
}
return 0;
}
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