OpenCores
URL https://opencores.org/ocsvn/openrisc/openrisc/trunk

Subversion Repositories openrisc

[/] [openrisc/] [trunk/] [rtos/] [ecos-2.0/] [doc/] [html/] [ref/] [usbs-enum.html] - Blame information for rev 613

Go to most recent revision | Details | Compare with Previous | View Log

Line No. Rev Author Line
1 28 unneback 
<!-- Copyright (C) 2003 Red Hat, Inc.                                -->
2 
<!-- This material may be distributed only subject to the terms      -->
3 
<!-- and conditions set forth in the Open Publication License, v1.0  -->
4 
<!-- or later (the latest version is presently available at          -->
5 
<!-- http://www.opencontent.org/openpub/).                           -->
6 
<!-- Distribution of the work or derivative of the work in any       -->
7 
<!-- standard (paper) book form is prohibited unless prior           -->
8 
<!-- permission is obtained from the copyright holder.               -->
9 
<HTML
10 
><HEAD
11 
><TITLE
12 
>USB Enumeration Data</TITLE
13 
><meta name="MSSmartTagsPreventParsing" content="TRUE">
14 
<META
15 
NAME="GENERATOR"
16 
CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
17 
"><LINK
18 
REL="HOME"
19 
TITLE="eCos Reference Manual"
20 
HREF="ecos-ref.html"><LINK
21 
REL="UP"
22 
TITLE="eCos USB Slave Support"
23 
HREF="io-usb-slave.html"><LINK
24 
REL="PREVIOUS"
25 
TITLE="Introduction"
26 
HREF="usbs-intro.html"><LINK
27 
REL="NEXT"
28 
TITLE="Starting up a USB Device"
29 
HREF="usbs-start.html"></HEAD
30 
><BODY
31 
CLASS="REFENTRY"
32 
BGCOLOR="#FFFFFF"
33 
TEXT="#000000"
34 
LINK="#0000FF"
35 
VLINK="#840084"
36 
ALINK="#0000FF"
37 
><DIV
38 
CLASS="NAVHEADER"
39 
><TABLE
40 
SUMMARY="Header navigation table"
41 
WIDTH="100%"
42 
BORDER="0"
43 
CELLPADDING="0"
44 
CELLSPACING="0"
45 
><TR
46 
><TH
47 
COLSPAN="3"
48 
ALIGN="center"
49 
>eCos Reference Manual</TH
50 
></TR
51 
><TR
52 
><TD
53 
WIDTH="10%"
54 
ALIGN="left"
55 
VALIGN="bottom"
56 
><A
57 
HREF="usbs-intro.html"
58 
ACCESSKEY="P"
59 
>Prev</A
60 
></TD
61 
><TD
62 
WIDTH="80%"
63 
ALIGN="center"
64 
VALIGN="bottom"
65 
></TD
66 
><TD
67 
WIDTH="10%"
68 
ALIGN="right"
69 
VALIGN="bottom"
70 
><A
71 
HREF="usbs-start.html"
72 
ACCESSKEY="N"
73 
>Next</A
74 
></TD
75 
></TR
76 
></TABLE
77 
><HR
78 
ALIGN="LEFT"
79 
WIDTH="100%"></DIV
80 
><H1
81 
><A
82 
NAME="USBS-ENUM">USB Enumeration Data</H1
83 
><DIV
84 
CLASS="REFNAMEDIV"
85 
><A
86 
NAME="AEN16105"
87 
></A
88 
><H2
89 
>Name</H2
90 
>Enumeration Data&nbsp;--&nbsp;The USB enumeration data structures</DIV
91 
><DIV
92 
CLASS="REFSYNOPSISDIV"
93 
><A
94 
NAME="AEN16108"><H2
95 
>Synopsis</H2
96 
><TABLE
97 
BORDER="5"
98 
BGCOLOR="#E0E0F0"
99 
WIDTH="70%"
100 
><TR
101 
><TD
102 
><PRE
103 
CLASS="SYNOPSIS"
104 
>#include &lt;cyg/io/usb/usb.h&gt;
105 
#include &lt;cyg/io/usb/usbs.h&gt;
106 
 
107 
typedef struct usb_device_descriptor {
108 
    &#8230;
109 
} usb_device_descriptor __attribute__((packed));
110 
 
111 
typedef struct usb_configuration_descriptor {
112 
    &#8230;
113 
} usb_configuration_descriptor __attribute__((packed));
114 
 
115 
typedef struct usb_interface_descriptor {
116 
    &#8230;
117 
} usb_interface_descriptor __attribute__((packed));
118 
 
119 
typedef struct usb_endpoint_descriptor {
120 
    &#8230;
121 
} usb_endpoint_descriptor;
122 
 
123 
typedef struct usbs_enumeration_data {
124 
    usb_device_descriptor               device;
125 
    int                                 total_number_interfaces;
126 
    int                                 total_number_endpoints;
127 
    int                                 total_number_strings;
128 
    const usb_configuration_descriptor* configurations;
129 
    const usb_interface_descriptor*     interfaces;
130 
    const usb_endpoint_descriptor*      endpoints;
131 
    const unsigned char**               strings;
132 
} usbs_enumeration_data;</PRE
133 
></TD
134 
></TR
135 
></TABLE
136 
></DIV
137 
><DIV
138 
CLASS="REFSECT1"
139 
><A
140 
NAME="AEN16110"
141 
></A
142 
><H2
143 
>USB Enumeration Data</H2
144 
><P
145 
>When a USB host detects that a peripheral has been plugged in or
146 
powered up, one of the first steps is to ask the peripheral to
147 
describe itself by supplying enumeration data. Some of this data
148 
depends on the class of peripheral. Other fields are vendor-specific.
149 
There is also a dependency on the hardware, specifically which
150 
endpoints are available should be used. In general it is not possible
151 
for generic code to provide this information, so it is the
152 
responsibility of application code to provide a suitable
153 
<SPAN
154 
CLASS="STRUCTNAME"
155 
>usbs_enumeration_data</SPAN
156 
> data structure and
157 
install it in the endpoint 0 data structure during initialization.
158 
This must happen before the USB device is enabled by a call to
159 
<TT
160 
CLASS="FUNCTION"
161 
>usbs_start</TT
162 
>, for example:</P
163 
><TABLE
164 
BORDER="5"
165 
BGCOLOR="#E0E0F0"
166 
WIDTH="70%"
167 
><TR
168 
><TD
169 
><PRE
170 
CLASS="PROGRAMLISTING"
171 
>const usbs_enumeration_data usb_enum_data = {
172 
    &#8230;
173 
};
174 
 
175 
int
176 
main(int argc, char** argv)
177 
{
178 
    usbs_sa11x0_ep0.enumeration_data = &amp;usb_enum_data;
179 
    &#8230;
180 
    usbs_start(&amp;usbs_sa11x0_ep0);
181 
    &#8230;
182 
}</PRE
183 
></TD
184 
></TR
185 
></TABLE
186 
><P
187 
>For most applications the enumeration data will be static, although
188 
the <SPAN
189 
CLASS="STRUCTNAME"
190 
>usbs_enumeration_data</SPAN
191 
> structure can be
192 
filled in at run-time if necessary. Full details of the enumeration
193 
data can be found in the Universal Serial Bus specification obtainable
194 
from the <A
195 
HREF="http://www.usb.org/"
196 
TARGET="_top"
197 
>USB Implementers Forum web
198 
site</A
199 
>, although the meaning of most fields is fairly obvious.
200 
The various data structures and utility macros are defined in the
201 
header files <TT
202 
CLASS="FILENAME"
203 
>cyg/io/usb/usb.h</TT
204 
>
205 
and <TT
206 
CLASS="FILENAME"
207 
>cyg/io/usb/usbs.h</TT
208 
>. Note
209 
that the example code below makes use of the gcc labelled element
210 
extension.</P
211 
><DIV
212 
CLASS="REFSECT2"
213 
><A
214 
NAME="AEN16121"
215 
></A
216 
><H3
217 
><SPAN
218 
CLASS="STRUCTNAME"
219 
>usb_device_descriptor</SPAN
220 
></H3
221 
><P
222 
>The main information about a USB peripheral comes from a single
223 
<SPAN
224 
CLASS="STRUCTNAME"
225 
>usb_device_descriptor</SPAN
226 
> structure, which is
227 
embedded in the <SPAN
228 
CLASS="STRUCTNAME"
229 
>usbs_enumeration_data</SPAN
230 
>
231 
structure. A typical example might look like this:</P
232 
><TABLE
233 
BORDER="5"
234 
BGCOLOR="#E0E0F0"
235 
WIDTH="70%"
236 
><TR
237 
><TD
238 
><PRE
239 
CLASS="PROGRAMLISTING"
240 
>const usbs_enumeration_data usb_enum_data = {
241 
    {
242 
        length:                 USB_DEVICE_DESCRIPTOR_LENGTH,
243 
        type:                   USB_DEVICE_DESCRIPTOR_TYPE,
244 
        usb_spec_lo:            USB_DEVICE_DESCRIPTOR_USB11_LO,
245 
        usb_spec_hi:            USB_DEVICE_DESCRIPTOR_USB11_HI,
246 
        device_class:           USB_DEVICE_DESCRIPTOR_CLASS_VENDOR,
247 
        device_subclass:        USB_DEVICE_DESCRIPTOR_SUBCLASS_VENDOR,
248 
        device_protocol:        USB_DEVICE_DESCRIPTOR_PROTOCOL_VENDOR,
249 
        max_packet_size:        8,
250 
        vendor_lo:              0x42,
251 
        vendor_hi:              0x42,
252 
        product_lo:             0x42,
253 
        product_hi:             0x42,
254 
        device_lo:              0x00,
255 
        device_hi:              0x01,
256 
        manufacturer_str:       1,
257 
        product_str:            2,
258 
        serial_number_str:      0,
259 
        number_configurations:  1
260 
    },
261 
    &#8230;
262 
};</PRE
263 
></TD
264 
></TR
265 
></TABLE
266 
><P
267 
>The length and type fields are specified by the USB standard. The
268 
<TT
269 
CLASS="STRUCTFIELD"
270 
><I
271 
>usb_spec_lo</I
272 
></TT
273 
> and
274 
<TT
275 
CLASS="STRUCTFIELD"
276 
><I
277 
>usb_spec_hi</I
278 
></TT
279 
> fields identify the particular
280 
revision of the standard that the peripheral implements, for example
281 
revision 1.1.</P
282 
><P
283 
>The device class, subclass, and protocol fields are used by generic
284 
host-side USB software to determine which host-side device driver
285 
should be loaded to interact with the peripheral. A number of standard
286 
classes are defined, for example mass-storage devices and
287 
human-interface devices. If a peripheral implements one of the
288 
standard classes then a standard existing host-side device driver may
289 
exist, eliminating the need to write a custom driver. The value
290 
<TT
291 
CLASS="LITERAL"
292 
>0xFF</TT
293 
> (<TT
294 
CLASS="LITERAL"
295 
>VENDOR</TT
296 
>) is reserved for
297 
peripherals that implement a vendor-specific protocol rather than a
298 
standard one. Such peripherals will require a custom host-side device
299 
driver. The value <TT
300 
CLASS="LITERAL"
301 
>0x00</TT
302 
>
303 
(<TT
304 
CLASS="LITERAL"
305 
>INTERFACE</TT
306 
>) is reserved and indicates that the
307 
protocol used by the peripheral is defined at the interface level
308 
rather than for the peripheral as a whole.</P
309 
><P
310 
>The <TT
311 
CLASS="STRUCTFIELD"
312 
><I
313 
>max_package_size</I
314 
></TT
315 
> field specifies the
316 
maximum length of a control message. There is a lower bound of eight
317 
bytes, and typical hardware will not support anything larger because
318 
control messages are usually small and not performance-critical.</P
319 
><P
320 
>The <TT
321 
CLASS="STRUCTFIELD"
322 
><I
323 
>vendor_lo</I
324 
></TT
325 
> and
326 
<TT
327 
CLASS="STRUCTFIELD"
328 
><I
329 
>vendor_hi</I
330 
></TT
331 
> fields specify a vendor id, which
332 
must be obtained from the USB Implementor's Forum. The numbers used in
333 
the code fragment above are examples only and must not be used in real
334 
USB peripherals. The product identifier is determined by the vendor,
335 
and different USB peripherals should use different identifiers. The
336 
device identifier field should indicate a release number in
337 
binary-coded decimal.</P
338 
><P
339 
>The above fields are all numerical in nature. A USB peripheral can
340 
also provide a number of strings as described <A
341 
HREF="usbs-enum.html#AEN16196"
342 
>below</A
343 
>, for example the name of the
344 
vendor can be provided. The various <TT
345 
CLASS="STRUCTFIELD"
346 
><I
347 
>_str</I
348 
></TT
349 
>
350 
fields act as indices into an array of strings, with index 0
351 
indicating that no string is available. </P
352 
><P
353 
>A typical USB peripheral involves just a single configuration. However
354 
more complicated peripherals can support multiple configurations. Only
355 
one configuration will be active at any one time, and the host will
356 
switch between them as appropriate. If a peripheral does involve
357 
multiple configurations then typically it will be the responsibility
358 
of application code to <A
359 
HREF="usbs-control.html#AEN16582"
360 
>handle</A
361 
> the standard
362 
set-configuration control message.</P
363 
></DIV
364 
><DIV
365 
CLASS="REFSECT2"
366 
><A
367 
NAME="AEN16146"
368 
></A
369 
><H3
370 
><SPAN
371 
CLASS="STRUCTNAME"
372 
>usb_configuration_descriptor</SPAN
373 
></H3
374 
><P
375 
>A USB peripheral involves at least one and possible several different
376 
configurations. The <SPAN
377 
CLASS="STRUCTNAME"
378 
>usbs_enumeration_data</SPAN
379 
>
380 
structure requires a pointer to an array, possibly of length 1, of
381 
<SPAN
382 
CLASS="STRUCTNAME"
383 
>usb_configuration_descriptor</SPAN
384 
> structures.
385 
Usually a single structure suffices:</P
386 
><TABLE
387 
BORDER="5"
388 
BGCOLOR="#E0E0F0"
389 
WIDTH="70%"
390 
><TR
391 
><TD
392 
><PRE
393 
CLASS="PROGRAMLISTING"
394 
>const usb_configuration_descriptor usb_configuration = {
395 
    length:             USB_CONFIGURATION_DESCRIPTOR_LENGTH,
396 
    type:               USB_CONFIGURATION_DESCRIPTOR_TYPE,
397 
    total_length_lo:    USB_CONFIGURATION_DESCRIPTOR_TOTAL_LENGTH_LO(1, 2),
398 
    total_length_hi:    USB_CONFIGURATION_DESCRIPTOR_TOTAL_LENGTH_HI(1, 2),
399 
    number_interfaces:  1,
400 
    configuration_id:   1,
401 
    configuration_str:  0,
402 
    attributes:         USB_CONFIGURATION_DESCRIPTOR_ATTR_REQUIRED |
403 
                        USB_CONFIGURATION_DESCRIPTOR_ATTR_SELF_POWERED,
404 
    max_power:          50
405 
};
406 
 
407 
const usbs_enumeration_data usb_enum_data = {
408 
    &#8230;
409 
    configurations:             &amp;usb_configuration,
410 
    &#8230;
411 
};</PRE
412 
></TD
413 
></TR
414 
></TABLE
415 
><P
416 
>The values for the <TT
417 
CLASS="STRUCTFIELD"
418 
><I
419 
>length</I
420 
></TT
421 
> and
422 
<TT
423 
CLASS="STRUCTFIELD"
424 
><I
425 
>type</I
426 
></TT
427 
> fields are determined by the standard.
428 
The <TT
429 
CLASS="STRUCTFIELD"
430 
><I
431 
>total_length</I
432 
></TT
433 
> field depends on the
434 
number of interfaces and endpoints used by this configuration, and
435 
convenience macros are provided to calculate this: the first argument
436 
to the macros specify the number of interfaces, the second the number
437 
of endpoints. The <TT
438 
CLASS="STRUCTFIELD"
439 
><I
440 
>number_interfaces</I
441 
></TT
442 
> field
443 
is self-explanatory. If the peripheral involves multiple
444 
configurations then each one must have a unique id, and this will be
445 
used in the set-configuration control message. The id
446 
<TT
447 
CLASS="LITERAL"
448 
>0</TT
449 
> is reserved, and a set-configuration control
450 
message that uses this id indicates that the peripheral should be
451 
inactive. Configurations can have a string description if required.
452 
The <TT
453 
CLASS="STRUCTFIELD"
454 
><I
455 
>attributes</I
456 
></TT
457 
> field must have the
458 
<TT
459 
CLASS="LITERAL"
460 
>REQUIRED</TT
461 
> bit set; the
462 
<TT
463 
CLASS="LITERAL"
464 
>SELF_POWERED</TT
465 
> bit informs the host that the
466 
peripheral has its own power supply and will not draw any power over
467 
the bus, leaving more bus power available to other peripherals; the
468 
<TT
469 
CLASS="LITERAL"
470 
>REMOTE_WAKEUP</TT
471 
> bit is used if the peripheral can
472 
interrupt the host when the latter is in power-saving mode. For
473 
peripherals that are not self-powered, the
474 
<TT
475 
CLASS="STRUCTFIELD"
476 
><I
477 
>max_power</I
478 
></TT
479 
> field specifies the power
480 
requirements in units of 2mA.</P
481 
></DIV
482 
><DIV
483 
CLASS="REFSECT2"
484 
><A
485 
NAME="AEN16164"
486 
></A
487 
><H3
488 
><SPAN
489 
CLASS="STRUCTNAME"
490 
>usb_interface_descriptor</SPAN
491 
></H3
492 
><P
493 
>A USB configuration involves one or more interfaces, typically
494 
corresponding to different streams of data. For example, one interface
495 
might involve video data while another interface is for audio.
496 
Multiple interfaces in a single configuration will be active at the
497 
same time.</P
498 
><TABLE
499 
BORDER="5"
500 
BGCOLOR="#E0E0F0"
501 
WIDTH="70%"
502 
><TR
503 
><TD
504 
><PRE
505 
CLASS="PROGRAMLISTING"
506 
>const usb_interface_descriptor usb_interface = {
507 
    length:             USB_INTERFACE_DESCRIPTOR_LENGTH,
508 
    type:               USB_INTERFACE_DESCRIPTOR_TYPE,
509 
    interface_id:       0,
510 
    alternate_setting:  0,
511 
    number_endpoints:   2,
512 
    interface_class:    USB_INTERFACE_DESCRIPTOR_CLASS_VENDOR,
513 
    interface_subclass: USB_INTERFACE_DESCRIPTOR_SUBCLASS_VENDOR,
514 
    interface_protocol: USB_INTERFACE_DESCRIPTOR_PROTOCOL_VENDOR,
515 
    interface_str:      0
516 
};
517 
 
518 
const usbs_enumeration_data usb_enum_data = {
519 
    &#8230;
520 
    total_number_interfaces:    1,
521 
    interfaces:                 &amp;usb_interface,
522 
    &#8230;
523 
};</PRE
524 
></TD
525 
></TR
526 
></TABLE
527 
><P
528 
>Again, the <TT
529 
CLASS="STRUCTFIELD"
530 
><I
531 
>length</I
532 
></TT
533 
> and
534 
<TT
535 
CLASS="STRUCTFIELD"
536 
><I
537 
>type</I
538 
></TT
539 
> fields are specified by the standard.
540 
Each interface within a configuration requires its own id. However, a
541 
given interface may have several alternate settings, in other words
542 
entries in the interfaces array with the same id but different
543 
<TT
544 
CLASS="STRUCTFIELD"
545 
><I
546 
>alternate_setting</I
547 
></TT
548 
> fields. For example,
549 
there might be one setting which requires a bandwidth of 100K/s and
550 
another setting that only needs 50K/s. The host can use the standard
551 
set-interface control message to choose the most appropriate setting.
552 
The handling of this request is the responsibility of higher-level
553 
code, so the application may have to <A
554 
HREF="usbs-control.html#AEN16582"
555 
>install</A
556 
> its own handler.</P
557 
><P
558 
>The number of endpoints used by an interface is specified in the
559 
<TT
560 
CLASS="STRUCTFIELD"
561 
><I
562 
>number_endpoints</I
563 
></TT
564 
> field. Exact details of
565 
which endpoints are used is held in a separate array of endpoint
566 
descriptors. The class, subclass and protocol fields are used by
567 
host-side code to determine which host-side device driver should
568 
handle this specific interface. Usually this is determined on a
569 
per-peripheral basis in the
570 
<SPAN
571 
CLASS="STRUCTNAME"
572 
>usb_device_descriptor</SPAN
573 
> structure, but that can
574 
defer the details to individual interfaces. A per-interface string
575 
is allowed as well.</P
576 
><P
577 
>For USB peripherals involving multiple configurations, the array of
578 
<SPAN
579 
CLASS="STRUCTNAME"
580 
>usb_interface_descriptor</SPAN
581 
> structures should
582 
first contain all the interfaces for the first configuration, then all
583 
the interfaces for the second configuration, and so on.</P
584 
></DIV
585 
><DIV
586 
CLASS="REFSECT2"
587 
><A
588 
NAME="AEN16179"
589 
></A
590 
><H3
591 
><SPAN
592 
CLASS="STRUCTNAME"
593 
>usb_endpoint_descriptor</SPAN
594 
></H3
595 
><P
596 
>The host also needs information about which endpoint should be used
597 
for what. This involves an array of endpoint descriptors:</P
598 
><TABLE
599 
BORDER="5"
600 
BGCOLOR="#E0E0F0"
601 
WIDTH="70%"
602 
><TR
603 
><TD
604 
><PRE
605 
CLASS="PROGRAMLISTING"
606 
>const usb_endpoint_descriptor usb_endpoints[] = {
607 
    {
608 
        length:         USB_ENDPOINT_DESCRIPTOR_LENGTH,
609 
        type:           USB_ENDPOINT_DESCRIPTOR_TYPE,
610 
        endpoint:       USB_ENDPOINT_DESCRIPTOR_ENDPOINT_OUT | 1,
611 
        attributes:     USB_ENDPOINT_DESCRIPTOR_ATTR_BULK,
612 
        max_packet_lo:  64,
613 
        max_packet_hi:  0,
614 
        interval:       0
615 
    },
616 
    {
617 
        length:         USB_ENDPOINT_DESCRIPTOR_LENGTH,
618 
        type:           USB_ENDPOINT_DESCRIPTOR_TYPE,
619 
        endpoint:       USB_ENDPOINT_DESCRIPTOR_ENDPOINT_IN | 2,
620 
        attributes:     USB_ENDPOINT_DESCRIPTOR_ATTR_BULK,
621 
        max_packet_lo:  64,
622 
        max_packet_hi:  0,
623 
        interval:       0
624 
    }
625 
};
626 
 
627 
const usbs_enumeration_data usb_enum_data = {
628 
    &#8230;
629 
    total_number_endpoints:     2,
630 
    endpoints:                  usb_endpoints,
631 
    &#8230;
632 
};</PRE
633 
></TD
634 
></TR
635 
></TABLE
636 
><P
637 
>As usual the values for the <TT
638 
CLASS="STRUCTFIELD"
639 
><I
640 
>length</I
641 
></TT
642 
> and
643 
<TT
644 
CLASS="STRUCTFIELD"
645 
><I
646 
>type</I
647 
></TT
648 
> fields are specified by the standard.
649 
The <TT
650 
CLASS="STRUCTFIELD"
651 
><I
652 
>endpoint</I
653 
></TT
654 
> field gives both the endpoint
655 
number and the direction, so in the above example endpoint 1 is used
656 
for OUT (host to peripheral) transfers and endpoint 2 is used for IN
657 
(peripheral to host) transfers. The
658 
<TT
659 
CLASS="STRUCTFIELD"
660 
><I
661 
>attributes</I
662 
></TT
663 
> field indicates the USB protocol
664 
that should be used on this endpoint: <TT
665 
CLASS="LITERAL"
666 
>CONTROL</TT
667 
>,
668 
<TT
669 
CLASS="LITERAL"
670 
>ISOCHRONOUS</TT
671 
>, <TT
672 
CLASS="LITERAL"
673 
>BULK</TT
674 
> or
675 
<TT
676 
CLASS="LITERAL"
677 
>INTERRUPT</TT
678 
>. The
679 
<TT
680 
CLASS="STRUCTFIELD"
681 
><I
682 
>max_packet</I
683 
></TT
684 
> field specifies the maximum size
685 
of a single USB packet. For bulk transfers this will typically be 64
686 
bytes. For isochronous transfers this can be up to 1023 bytes. For
687 
interrupt transfers it can be up to 64 bytes, although usually a
688 
smaller value will be used. The <TT
689 
CLASS="STRUCTFIELD"
690 
><I
691 
>interval</I
692 
></TT
693 
>
694 
field is ignored for control and bulk transfers. For isochronous
695 
transfers it should be set to 1. For interrupt transfers it can be a
696 
value between 1 and 255, and indicates the number of milliseconds
697 
between successive polling operations.</P
698 
><P
699 
>For USB peripherals involving multiple configurations or interfaces
700 
the array of endpoint descriptors should be organized sequentially:
701 
first the endpoints corresponding to the first interface of the first
702 
configuration, then the second interface in that configuration, and so
703 
on; then all the endpoints for all the interfaces in the second
704 
configuration; etc.</P
705 
></DIV
706 
><DIV
707 
CLASS="REFSECT2"
708 
><A
709 
NAME="AEN16196"
710 
></A
711 
><H3
712 
>Strings</H3
713 
><P
714 
>The enumeration data can contain a number of strings with additional
715 
information. Unicode encoding is used for the strings, and it is
716 
possible for a peripheral to supply a given string in multiple
717 
languages using the appropriate characters. The first two bytes of
718 
each string give a length and type field. The first string is special;
719 
after the two bytes header it consists of an array of 2-byte language
720 
id codes, indicating the supported languages. The language code
721 
0x0409 corresponds to English (United States). </P
722 
><TABLE
723 
BORDER="5"
724 
BGCOLOR="#E0E0F0"
725 
WIDTH="70%"
726 
><TR
727 
><TD
728 
><PRE
729 
CLASS="PROGRAMLISTING"
730 
>const unsigned char* usb_strings[] = {
731 
    "\004\003\011\004",
732 
    "\020\003R\000e\000d\000 \000H\000a\000t\000"
733 
};
734 
 
735 
const usbs_enumeration_data usb_enum_data = {
736 
    &#8230;
737 
    total_number_strings:       2,
738 
    strings:                    usb_strings,
739 
    &#8230;
740 
};</PRE
741 
></TD
742 
></TR
743 
></TABLE
744 
><P
745 
>The default handler for standard control messages assumes that the
746 
peripheral only uses a single language. If this is not the case then
747 
higher-level code will have to handle the standard get-descriptor
748 
control messages when a string descriptor is requested.</P
749 
></DIV
750 
><DIV
751 
CLASS="REFSECT2"
752 
><A
753 
NAME="AEN16201"
754 
></A
755 
><H3
756 
><SPAN
757 
CLASS="STRUCTNAME"
758 
>usbs_enumeration_data</SPAN
759 
></H3
760 
><P
761 
>The <SPAN
762 
CLASS="STRUCTNAME"
763 
>usbs_enumeration_data</SPAN
764 
> data structure
765 
collects together all the various descriptors that make up the
766 
enumeration data. It is the responsibility of application code to
767 
supply a suitable data structure and install it in the control
768 
endpoints's <TT
769 
CLASS="STRUCTFIELD"
770 
><I
771 
>enumeration_data</I
772 
></TT
773 
> field before
774 
the USB device is started.</P
775 
></DIV
776 
></DIV
777 
><DIV
778 
CLASS="NAVFOOTER"
779 
><HR
780 
ALIGN="LEFT"
781 
WIDTH="100%"><TABLE
782 
SUMMARY="Footer navigation table"
783 
WIDTH="100%"
784 
BORDER="0"
785 
CELLPADDING="0"
786 
CELLSPACING="0"
787 
><TR
788 
><TD
789 
WIDTH="33%"
790 
ALIGN="left"
791 
VALIGN="top"
792 
><A
793 
HREF="usbs-intro.html"
794 
ACCESSKEY="P"
795 
>Prev</A
796 
></TD
797 
><TD
798 
WIDTH="34%"
799 
ALIGN="center"
800 
VALIGN="top"
801 
><A
802 
HREF="ecos-ref.html"
803 
ACCESSKEY="H"
804 
>Home</A
805 
></TD
806 
><TD
807 
WIDTH="33%"
808 
ALIGN="right"
809 
VALIGN="top"
810 
><A
811 
HREF="usbs-start.html"
812 
ACCESSKEY="N"
813 
>Next</A
814 
></TD
815 
></TR
816 
><TR
817 
><TD
818 
WIDTH="33%"
819 
ALIGN="left"
820 
VALIGN="top"
821 
>Introduction</TD
822 
><TD
823 
WIDTH="34%"
824 
ALIGN="center"
825 
VALIGN="top"
826 
><A
827 
HREF="io-usb-slave.html"
828 
ACCESSKEY="U"
829 
>Up</A
830 
></TD
831 
><TD
832 
WIDTH="33%"
833 
ALIGN="right"
834 
VALIGN="top"
835 
>Starting up a USB Device</TD
836 
></TR
837 
></TABLE
838 
></DIV
839 
></BODY
840 
></HTML
841 
>

powered by: WebSVN 2.1.0

© copyright 1999-2024 OpenCores.org, equivalent to Oliscience, all rights reserved. OpenCores®, registered trademark.