📄 linux设备驱动之usb主机控制器驱动分析-(6)_linux技术文章_linux_操作系统6.htm
字号:
invalid)”.也就是表示,它的后面已经没有有效项了.不要再往后面去遍历了.其实就是一个终止项<BR> <BR>
//skel_term_qh = skelqh[10]<BR>
uhci->skel_term_qh->link =
LINK_TO_QH(uhci->skel_term_qh);<BR> <BR> /* This
dummy TD is to work around a bug in Intel PIIX controllers
*/<BR> uhci_fill_td(uhci->term_td, 0, uhci_explen(0)
|<BR>
(0x7f << TD_TOKEN_DEVADDR_SHIFT) | USB_PID_IN,
0);<BR> //term_td后面已经没有数据了<BR>
uhci->term_td->link = UHCI_PTR_TERM;<BR>
uhci->skel_async_qh->element = uhci->skel_term_qh->element
=<BR>
LINK_TO_TD(uhci->term_td);<BR>Skel_term_qh定义成skelqh[10].即uhci->skelqh[
]的最后一项.它自己指向了自己.<BR>然后对于uhci->term_td是Intel
PIIX的一个BUG.这部份就不再详细分析了.最后将uhci->term_td挂上了uhci->skelqh[9]和uhci->skelqh[10]<BR>
/*<BR> * Fill the frame list: make all entries
point to the proper<BR> * interrupt
queue.<BR> */<BR> for (i =
0; i < UHCI_NUMFRAMES; i++)
{<BR> <BR> /* Only place we
don't use the frame list routines
*/<BR> uhci->frame[i] =
uhci_frame_skel_link(uhci, i);<BR>
}<BR> <BR> /*<BR> *
Some architectures require a full mb() to enforce completion
of<BR> * the memory writes above before the I/O
transfers in configure_hc().<BR>
*/<BR> mb();<BR> <BR>
configure_hc(uhci);<BR> uhci->is_initialized =
1;<BR> start_rh(uhci);<BR>
return
0;<BR>最后,将初始化完成的TD和QH项挂到uhci->frame[].然后再调用configure_hc和start_rh来配置UHCI和启用UHCI.<BR> <BR>/*<BR> *
error exits:<BR> */<BR>err_alloc_skelqh:<BR> for (i
= 0; i < UHCI_NUM_SKELQH; i++)
{<BR> if
(uhci->skelqh[i])<BR>
uhci_free_qh(uhci, uhci->skelqh[i]);<BR>
}<BR> <BR> uhci_free_td(uhci,
uhci->term_td);<BR> <BR>err_alloc_term_td:<BR>
dma_pool_destroy(uhci->qh_pool);<BR> <BR>err_create_qh_pool:<BR>
dma_pool_destroy(uhci->td_pool);<BR> <BR>err_create_td_pool:<BR>
kfree(uhci->frame_cpu);<BR> <BR>err_alloc_frame_cpu:A<BR>
dma_free_coherent(uhci_dev(uhci),<BR>
UHCI_NUMFRAMES *
sizeof(*uhci->frame),<BR>
uhci->frame,
uhci->frame_dma_handle);<BR> <BR>err_alloc_frame:<BR>
debugfs_remove(uhci->dentry);<BR> <BR>err_create_debug_entry:<BR>
return retval;<BR>}<BR>这里的TD,QH交错复杂,很容易把头看昏.画了个图.如下 :<BR><IMG
src="linux设备驱动之USB主机控制器驱动分析-(6)_Linux技术文章_Linux_操作系统6.files/080909094427.jpg"
width=500 onload="javascript:if(this.width>500)this.width=500;"
border=0><BR> <BR>从上图中可以看出,skelqh[]数组的第0项和第1项是没有经过初始化的.而skelqh[10]又是指向它本身的结点.<BR>经过skelqh[]的初始化后.就可以将它和frmae[]关联起来了.<BR>如下面代码片段所示:<BR>
for (i = 0; i < UHCI_NUMFRAMES; i++)
{<BR> <BR> /* Only place we
don't use the frame list routines
*/<BR> uhci->frame[i] =
uhci_frame_skel_link(uhci, i);<BR>
}<BR>Uhci_frame_skel_link()的代码如下所示:<BR>static __le32 uhci_frame_skel_link(struct
uhci_hcd *uhci, int frame)<BR>{<BR> int
skelnum;<BR> skelnum = 8 - (int) __ffs(frame |
UHCI_NUMFRAMES);<BR> if (skelnum <=
1)<BR> skelnum =
9;<BR> return
LINK_TO_QH(uhci->skelqh[skelnum]);<BR>}<BR>这个函数虽然很短小,但是算法却很复杂.<BR>首先来看一下这个函数要做什么事情:<BR>我们在前面说过,int128,int64,int32……int4,int2,int1这样8个QH.我们在后面看到.会将uhci->frame的物理地址存放到UHCI控制器的Frame
List Base Address Register中.所以现在要做的事情就是将这些QH与uhci->frame[
]关联起来.必须要按照相应的时间间隔将QH插入到uhci->frame[]中.例如,例如如果frame[]的n存放int128的QH,那么下一个int128的QH就必须要放到n+128的位置.很明显,对于int1是可以随便放的,也可放可不放.因为int1链接在所有的间隔的QH后面.同时int1又可以单独存放到frame[]中.<BR>另外,从skelqh[2]~skelqh[9]分别表示int128~int1.对于skelqh[0]和skelqh[1]是不需要用到的,而且8-
(int) __ffs(frame | UHCI_NUMFRAMES)不可能大于9.所以,</P>
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