USB host control

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app:
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          USB设备驱动程序      // 知道数据含义
内核 --------------------------------------
          USB总线驱动程序      // 1. 识别, 2. 找到匹配的设备驱动, 3. 提供USB读写函数 (它不知道数据含义)
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           USB主机控制器
           UHCI OHCI EHCI
硬件        -----------
              USB设备

UHCI: intel, 低速(1.5Mbps)/全速(12Mbps)
OHCI: microsoft 低速/全速
EHCI: 高速(480Mbps)

USB总线驱动程序相当于USB主机控制器的驱动程序。
对于Linux USB主机驱动程序可以分析

Freezer
Upon entering a suspended state the system will freeze all tasks. This is done by delivering pseudosignals. This affects kernel threads, too. To successfully freeze a kernel thread the thread has to check for the pseudo signal and enter the refrigerator. Code to do this looks like this:
do { hub_events();
wait_event_interruptible(khubd_wait, !list_empty(&hub_event_list)); try_to_freeze(); } while (!signal_pending(current));
from drivers/usb/core/hub.c::hub_thread()

在内核目录下搜:
grep "USB device using" * -nR
drivers/usb/core/hub.c:2186: "%s %s speed %sUSB device using %s and address %d\n",

hub_irq //最终还是irq 中断得到USB设备来了。
kick_khubd
  hub_thread
   hub_events
    hub_port_connect_change

     udev = usb_alloc_dev(hdev, hdev->bus, port1);
        dev->dev.bus = &usb_bus_type;

     choose_address(udev); // 给新设备分配编号(地址)


     hub_port_init   // usb 1-1: new full speed USB device using s3c2410-ohci and address 3

      hub_set_address // 把编号(地址)告诉USB设备

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