Thread: [Libusb-win32-devel] Understanding iIsochronous transfer with libusb-win32

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I am in the process of writing a simple isochronous transfer  firmware for
Microchip PICkit 2 (PIC18F2550). I need a host application to test it.
http://forum.microchip.com/tm.aspx?m=270049&mpage=2

Based on some of the examples Stephan posted here, I come out the
following test program and it seems to work. However, I do not quite
understand the code since I do not quite understand isochronous transfer.
Why we need three context? What is the benefit? Now three buffers
contain the same data.

I know the firmware is not that useful yet since it does not implement
double buffer.

<code>
#include <usb.h>

#define VERSION "0.1.0"
#define VENDOR_ID 0x04D8
#define PRODUCT_ID 0x0080
#define INTERFACE 0
#define BUFFER_SIZE 65

usb_dev_handle *find_pickit2_isoc();

usb_dev_handle* setup_libusb_access() {
    usb_dev_handle *pickit2_isoc;

	usb_set_debug(255);
    usb_init();
    usb_find_busses();
    usb_find_devices();

    if(!(pickit2_isoc = find_pickit2_isoc())) {
		printf("Couldn't find the mouse, Exiting\n");
		return NULL;
	}

	if (usb_set_configuration(pickit2_isoc, 1) < 0) {
		printf("Could not set configuration 1 : %s\n");
		return NULL;
	}

	if (usb_claim_interface(pickit2_isoc, INTERFACE) < 0) {
		printf("Could not claim interface: %s\n");
		return NULL;
	}

	return pickit2_isoc;
}

usb_dev_handle *find_pickit2_isoc()
{
    struct usb_bus *bus;
	struct usb_device *dev;

	for (bus = usb_busses; bus; bus = bus->next) {
    	for (dev = bus->devices; dev; dev = dev->next) {
   			if (dev->descriptor.idVendor == VENDOR_ID &&
		  		dev->descriptor.idProduct == PRODUCT_ID ) {
				usb_dev_handle *handle;
		  		printf("pickit2_isoc with Vendor Id: %x and Product Id: %x
found.\n", VENDOR_ID, PRODUCT_ID);
				if (!(handle = usb_open(dev))) {
					printf("Could not open USB device\n");
					return NULL;
				}

				return handle;
			}

		}
	}

	return NULL;
}

 void test_isochronous_async(usb_dev_handle *dev)
 {
   unsigned char buf0[640];
   unsigned char buf1[640];
   unsigned char buf2[640];

   int i;

   /* use three contexts for this example (more can be used) */
   void *context0 = NULL;
   void *context1 = NULL;
   void *context2 = NULL;

   /* write transfer (stream) */
/*
   usb_isochronous_setup_async(dev, &context0, 0x01);
   usb_isochronous_setup_async(dev, &context1, 0x01);
   usb_isochronous_setup_async(dev, &context2, 0x01);

   usb_submit_async(context0, buf0, sizeof(buf0));
   usb_submit_async(context1, buf1, sizeof(buf1));
   usb_submit_async(context2, buf2, sizeof(buf2));

   for(i = 0; i < 10; i++)
     {
       usb_reap_async(context0, 5000);
       usb_submit_async(context0, buf0, sizeof(buf0));

       usb_reap_async(context1, 5000);
       usb_submit_async(context1, buf1, sizeof(buf1));

       usb_reap_async(context2, 5000);
       usb_submit_async(context2, buf2, sizeof(buf2));
     }

   usb_reap_async(context0, 5000);
   usb_reap_async(context1, 5000);
   usb_reap_async(context2, 5000);

   usb_free_async(&context0);
   usb_free_async(&context1);
   usb_free_async(&context2);

*/

   /* read transfer (stream) */
   usb_isochronous_setup_async(dev, &context0, 0x81,64);
   usb_isochronous_setup_async(dev, &context1, 0x81,64);
   usb_isochronous_setup_async(dev, &context2, 0x81,64);

   usb_submit_async(context0, buf0, sizeof(buf0));
   usb_submit_async(context1, buf1, sizeof(buf1));
   usb_submit_async(context2, buf2, sizeof(buf2));

   for(i = 0; i < 10; i++)
     {
       usb_reap_async(context0, 5000);
       usb_submit_async(context0, buf0, sizeof(buf0));

       usb_reap_async(context1, 5000);
       usb_submit_async(context1, buf1, sizeof(buf1));

       usb_reap_async(context2, 5000);
       usb_submit_async(context2, buf2, sizeof(buf2));
     }

   for(i = 0; i < 640; i++) {
		printf(" %02x, %02x, %02x ", buf0[i],buf1[i],buf2[i]);
//		printf(" %02x, %02x, %02x ", buf0[i]);
		}

   usb_reap_async(context0, 5000);
   usb_reap_async(context1, 5000);
   usb_reap_async(context2, 5000);
   usb_free_async(&context0);
   usb_free_async(&context1);
   usb_free_async(&context2);

   /* release interface */
   usb_set_altinterface(dev, 0);
   usb_release_interface(dev, 0);
 }

int main(void)
{
	usb_dev_handle *pickit2_isoc;
	if ((pickit2_isoc = setup_libusb_access()) == NULL) {
		exit(-1);
	}
	test_isochronous_async(pickit2_isoc);
	usb_close(pickit2_isoc);

	return 0;
}

<device info>
DLL version:	0.1.12.1
Driver version:	0.1.12.1

bus/device  idVendor/idProduct
bus-0/\\.\libusb0-0001--0x04d8-0x0080     04D8/0080
- Manufacturer : Microchip Technology Inc.
- Product      : PICDEM FS USB Demo Board (C) 2004
  wTotalLength:         32
  bNumInterfaces:       1
  bConfigurationValue:  1
  iConfiguration:       0
  bmAttributes:         80h
  MaxPower:             50
    bInterfaceNumber:   0
    bAlternateSetting:  0
    bNumEndpoints:      2
    bInterfaceClass:    0
    bInterfaceSubClass: 0
    bInterfaceProtocol: 0
    iInterface:         0
      bEndpointAddress: 01h
      bmAttributes:     0dh
      wMaxPacketSize:   64
      bInterval:        1
      bRefresh:         0
      bSynchAddress:    0
      bEndpointAddress: 81h
      bmAttributes:     0dh
      wMaxPacketSize:   64
      bInterval:        1
      bRefresh:         0
      bSynchAddress:    0

Regards,
Xiaofan

Thread: [Libusb-win32-devel] Understanding iIsochronous transfer with libusb-win32

libusb-win32 is a port of libusb-0.1 under Windows

libusb-win32-devel