usb_get_max_pkts_per_isoc_request(9F)			   Kernel Functions for Drivers 		     usb_get_max_pkts_per_isoc_request(9F)

NAME

       usb_get_max_pkts_per_isoc_request - Get maximum number of packets allowed per isochronous request

SYNOPSIS

       #include <sys/usb/usba.h>

       uint_t usb_get_max_pkts_per_isoc_request(dev_info_t *dip);

INTERFACE LEVEL

       Solaris DDI specific (Solaris DDI)

PARAMETERS

       dip

	   Pointer to the device's dev_info structure.

DESCRIPTION

       The usb_get_max_pkts_per_isoc_request() function returns the maximum number of isochronous packets per request that the host control driver
       can support. This number can be used to determine the maximum amount of data which can	  be handled  by  a  single  isochronous  request.
       That length is found by:

       max = usb_get_max_pkts_per_isoc_request(dip) * endpoint_max_packet_size;

       where endpoint_max_packet_size is the wMaxPacketSize field of the isochronous endpoint over which the transfer will take        place.

RETURN VALUES

       On  success,  the usb_get_current_frame_number() function returns the maximum number of isochronous pkts per request. On failure it returns
       0. The function fails if dip is NULL.

CONTEXT

       May be called from user, kernel or interrupt context.

EXAMPLES

       /*
	* Set up to receive periodic isochronous data, requesting
	* the maximum amount for each transfer.
	*/

       int pkt;
       /* Get max packet size from endpoint descriptor. */
       uint_t ep_max_pkt_size = ep_descr.wMaxPacketSize;
       uint_t isoc_pkts_count = usb_get_max_pkts_per_isoc_request(dip);

       /*
	* Allocate an isoc request, specifying the max number of packets
	* and the greatest size transfer possible.
	*/
       usb_isoc_req_t *isoc_req = usb_alloc_isoc_req(dip,
	   isoc_pkts_count,
	   isoc_pkts_count * ep_max_pkt_size,
	   USB_FLAGS_SLEEP);

       /* Init each packet descriptor for maximum size. */
       for (pkt = 0; pkt < isoc_pkts_count; pkt++) {
	   isoc_req->isoc_pkt_descr[pkt].isoc_pkt_length = ep_max_pkt_size;

       }

       /* Set the length of a packet in the request too. */
       isoc_req->isoc_pkts_length = ep_max_pkt_size;

       /* Other isoc request initialization. */
       ...
       ...

       if (usb_pipe_isoc_xfer(pipe, isoc_req, USB_FLAGS_NOSLEEP) != USB_SUCCESS) {
	   ...
       }

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Architecture		     |PCI-based systems 	   |
       +-----------------------------+-----------------------------+
       |Interface stability	     |Evolving			   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWusb			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       attributes(5), usb_pipe_isoc_xfer(9F), usb_alloc_request(9F), usb_get_current_frame_number(9F). usb_ep_descr(9S), usb_isoc_request(9S)

SunOS 5.10							    5 Jan 2004				     usb_get_max_pkts_per_isoc_request(9F)