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

usb_get_max_pkts_per_isoc_request - Get maximum number of packets allowed per isochronous request

#include <sys/usb/usba.h>
uint_t usb_get_max_pkts_per_isoc_request(dev_info_t *dip);

illumos DDI specific (illumos DDI)

dip
Pointer to the device's dev_info structure.

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.

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.

May be called from user, kernel or interrupt context.


/*
 * 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) {
    ...
}

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

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

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)
November 10, 2016 OmniOS