📄 linux设备驱动之usb主机控制器驱动分析-(11)_linux技术文章_linux_操作系统11.htm
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skip_to_next_interface_descriptor;<BR> <BR> /*
Which interface entry is this? */<BR> intfc =
NULL;<BR> inum =
d->bInterfaceNumber;<BR>
//config->intf_cache保存着端点的相关信息<BR> for (i = 0; i <
config->desc.bNumInterfaces; ++i)
{<BR> if (inums[i] == inum)
{<BR>
intfc =
config->intf_cache[i];<BR>
break;<BR>
}<BR> }<BR>
//保存的端口总数超过了最大值,非法<BR> if (!intfc ||
intfc->num_altsetting >=
nalts[i])<BR> goto
skip_to_next_interface_descriptor;<BR> <BR> /*
Check for duplicate altsetting entries */<BR>
//标识字段<BR> asnum =
d->bAlternateSetting;<BR>
//如果存在相同的.非法<BR> for ((i = 0, alt =
&intfc->altsetting[0]);<BR>
i <
intfc->num_altsetting;<BR>
(++i, ++alt)) {<BR> if
(alt->desc.bAlternateSetting == asnum)
{<BR>
dev_warn(ddev, "Duplicate descriptor for config %d
"<BR>
"interface %d altsetting %d,
skipping\n",<BR>
cfgno, inum,
asnum);<BR>
goto
skip_to_next_interface_descriptor;<BR>
}<BR> }<BR> <BR>
//更新计数<BR>
++intfc->num_altsetting;<BR>
//如果合法的话,那alt就是指向一个空的接点描述符<BR> memcpy(&alt->desc,
d, USB_DT_INTERFACE_SIZE);<BR> <BR> /* Skip over
any Class Specific or Vendor Specific descriptors;<BR>
* find the first endpoint or interface descriptor
*/<BR> //下一个endpoint
descriptors的地址<BR> alt->extra =
buffer;<BR> i = find_next_descriptor(buffer, size,
USB_DT_ENDPOINT,<BR>
USB_DT_INTERFACE, &n);<BR>
//alt->extar+alt->extralen表示下一个描述符地址<BR>
alt->extralen = i;<BR> if (n >
0)<BR> dev_dbg(ddev, "skipped %d
descriptor%s after %s\n",<BR>
n, plural(n), "interface");<BR>
//下个intreface desp的地址<BR> buffer +=
i;<BR> size -= i;<BR> <BR>
//接口中端点描述符的个数.<FONT
size=3> </FONT>注意在这里将alt->desc.bNumEndpoints清0了<BR>
/* Allocate space for the right(?) number of endpoints
*/<BR> num_ep = num_ep_orig =
alt->desc.bNumEndpoints;<BR>
alt->desc.bNumEndpoints = 0;
/* Use as a counter */<BR> if (num_ep >
USB_MAXENDPOINTS) {<BR>
dev_warn(ddev, "too many endpoints for config %d interface %d
"<BR>
"altsetting %d: %d, using maximum allowed:
%d\n",<BR>
cfgno, inum, asnum, num_ep,
USB_MAXENDPOINTS);<BR> num_ep =
USB_MAXENDPOINTS;<BR>
}<BR> <BR> if (num_ep > 0)
{<BR> /* Can't allocate 0 bytes
*/<BR> len = sizeof(struct
usb_host_endpoint) *
num_ep;<BR> &#</P>
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