USB_GET_MAX_PKTS_PER_ISOC_REQUEST(9F) Kernel Functions for Drivers

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

illumos DDI specific (illumos 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_max_pkts_per_isoc_request() 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(7) for descriptions of the following attributes:


+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Architecture | PCI-based systems |
+--------------------+-------------------+
|Interface stability | Committed |
+--------------------+-------------------+

SEE ALSO

attributes(7), usb_alloc_request(9F),
usb_get_current_frame_number(9F), usb_pipe_isoc_xfer(9F),
usb_ep_descr(9S), usb_isoc_request(9S)

November 10, 2016
USB_GET_MAX_PKTS_PER_ISOC_REQUEST(9F)