我在使用cdc_acm驱动程序在USB端口上发送意外字符时遇到问题.更令人困惑的是,代码在Ubuntu 12.04(3.2内核)上运行良好但在Centos 6(3.6内核)上失败(这个问题的主题)
USB设备是Bluegiga BLED112蓝牙智能加密狗.它的嵌入式微控制器将在USB接口的任何意外输入时复位.
测试代码打开端口,写入4个字节(一个问候消息)并期望读取响应.读取永远不会完成,因为意外字符会导致设备重置,从而导致集线器丢弃设备并重新枚举.
要进行故障排除,这就是我所做的：
>下载cdc_acm驱动程序的源代码.添加了一堆printk调试消息和stack_dump来跟踪正在发生的事情.
>我rmmod’d“stock”cdc_acm并insmod’d我的仪器化模块.所有设备枚举工作,右驱动程序附加等.
>由于代码适用于Ubuntu 12.04 / Linux 3.2,我抓住了3.2 cdc_acm代码并在Centos 6 / Linux 3.6平台上编译了该模块.使用3.2模块而不是3.6模块并没有什么区别.我回到了3.6模块.
>用usbmon打开调试文件系统,观察USB流量.我可以看到USB接口上发送了额外的字符.
>要观察正在发生的事情,在cdc_acm模块中的printk之上,我已经合并了usb mon(cat / sys / kernel / debug / usb / usbmon / 3u | logger)的输出和测试应用程序的输出(scan_example / dev / ttyACM0 | logger -s)所以我有一个时间相关的调试跟踪流.
>在USB端点上发送的虚假字符是x5E x40 x5E x40 x5E x40 x5E x40 x41(在ASCII中它的^ @ ^ @ ^ @ ^ @ A)看起来像某种探测或试图引起调制解调器的注意这些在应用程序的write()导致将4个hello字节发送到结束点后立即发送字符.
>由于cdc_acm设备应该是调制解调器,我试图通过将其添加到cdc_acm.c中的usb_device_id acm_ids []来关闭调制解调器控制.
/* bluegiga BLED112*/
{ USB_DEVICE(0x2458, 0x0001),
.driver_info = NOT_A_MODEM,
},
>重新编译并insmod’d和syslog显示这被识别(怪癖是8),但功能没有变化.
NetowrkManager和调制解调器管理器都没有运行,但我仍然怀疑在某个地方有某种调制解调器控制功能,我只是不知道在哪里.
这是一个带注释的调试日志(MDV前缀那些我添加到cdc_acm的printk)
Feb 13 18:14:32 localhost kernel: MDV:cdc-acm acm_write_bulk
Feb 13 18:14:32 localhost kernel: MDV:cdc-acm acm_write_done
以下是应用程序00 00 00 01发送的4个字节
Feb 13 18:14:32 localhost cpcenter: df046a80 3672670191 C Bi:3:006:4 0 4 = 00000001
Feb 13 18:14:32 localhost cpcenter: 1360797272.669690 write: data2: len=0 contains:
……而这些额外的角色出乎意料地出现了5e 40 5e 40 5e 40 ……
Feb 13 18:14:32 localhost cpcenter: df046a80 3672670232 S Bi:3:006:4 -115 128 <
Feb 13 18:14:32 localhost cpcenter: f3cc5740 3672670297 S Bo:3:006:4 -115 1 = 5e
Feb 13 18:14:32 localhost cpcenter: df2e1300 3672670332 S Bo:3:006:4 -115 1 = 40
Feb 13 18:14:32 localhost cpcenter: f3cc5740 3672670347 C Bo:3:006:4 0 1 >
Feb 13 18:14:32 localhost cpcenter: f3cc5740 3672670392 S Bo:3:006:4 -115 1 = 5e
Feb 13 18:14:32 localhost cpcenter: df2e1180 3672670426 S Bo:3:006:4 -115 1 = 40
Feb 13 18:14:32 localhost cpcenter: df2e1c00 3672670461 S Bo:3:006:4 -115 1 = 5e
Feb 13 18:14:32 localhost cpcenter: df2e1840 3672670496 S Bo:3:006:4 -115 1 = 40
Feb 13 18:14:32 localhost cpcenter: df2e1300 3672670591 C Bo:3:006:4 0 1 >
在这一点上,我们得到了自发的脱节.
Feb 13 18:14:32 localhost kernel: usb 3-1: USB disconnect, device number 6
Feb 13 18:14:32 localhost kernel: MDV:cdc-acm acm_write_bulk
Feb 13 18:14:32 localhost kernel: MDV:cdc-acm acm_write_done
Feb 13 18:14:32 localhost kernel: MDV:cdc-acm read_bulk_callback
Feb 13 18:14:32 localhost kernel: MDV 1 acm_read_bulk_callback - urb 1, len 0
Feb 13 18:14:32 localhost kernel: MDV 3 acm_read_bulk_callback - non-zero urb status: -71
Feb 13 18:14:32 localhost kernel: MDV:cdc-acm acm_write_bulk
Feb 13 18:14:32 localhost kernel: MDV:cdc-acm acm_write_done
Feb 13 18:14:32 localhost kernel: MDV:cdc-acm read_bulk_callback
Feb 13 18:14:32 localhost kernel: MDV 1 acm_read_bulk_callback - urb 1, len 0
Feb 13 18:14:32 localhost kernel: MDV 3 acm_read_bulk_callback - non-zero urb status: -71
Feb 13 18:14:32 localhost kernel: MDV:cdc-acm acm_write_bulk
Feb 13 18:14:32 localhost kernel: MDV:cdc-acm acm_write_done
Feb 13 18:14:32 localhost kernel: MDV:cdc-acm read_bulk_callback
Feb 13 18:14:32 localhost kernel: MDV 1 acm_read_bulk_callback - urb 2, len 0
Feb 13 18:14:32 localhost cpcenter: df2e1d80 3672670629 S Bo:3:006:4 -115 1 = 5e
Feb 13 18:14:32 localhost kernel: MDV 3 acm_read_bulk_callback - non-zero urb status: -71
Feb 13 18:14:32 localhost cpcenter: df2e1300 3672670677 S Bo:3:006:4 -115 1 = 41
Feb 13 18:14:32 localhost cpcenter: f3cc5740 3672670802 C Bo:3:006:4 0 1 >
Feb 13 18:14:32 localhost cpcenter: df2e1180 3672671019 C Bo:3:006:4 0 1 >
Feb 13 18:14:32 localhost cpcenter: df2e1c00 3672671237 C Bo:3:006:4 0 1 >
Feb 13 18:14:32 localhost cpcenter: dfbf8c00 3672673193 C Ii:3:001:1 0:2048 1 = 02
Feb 13 18:14:32 localhost cpcenter: dfbf8c00 3672673207 S Ii:3:001:1 -115:2048 4 <
Feb 13 18:14:32 localhost cpcenter: f3c26c00 3672673221 S Ci:3:001:0 s a3 00 0000 0001 0004 4 <
Feb 13 18:14:32 localhost kernel: MDV:cdc-acm acm_disconnect
Feb 13 18:14:32 localhost kernel: Pid: 29, comm: khubd Tainted: G O 3.5.3-1.el6.elrepo.i686 #1
断开连接时的堆栈跟踪
Feb 13 18:14:32 localhost kernel: Call Trace:
Feb 13 18:14:32 localhost kernel: [<f82dabc5>] acm_disconnect+0x35/0x1f0 [cdc_acm]
Feb 13 18:14:32 localhost kernel: [<c13835db>] usb_unbind_interface+0x4b/0x180
Feb 13 18:14:32 localhost cpcenter: f3c26c00 3672673239 C Ci:3:001:0 0 4 = 00010100
Feb 13 18:14:32 localhost kernel: [<c1318bfb>] __device_release_driver+0x5b/0xb0
Feb 13 18:14:32 localhost kernel: [<c1318d05>] device_release_driver+0x25/0x40
Feb 13 18:14:32 localhost kernel: [<c1317f0c>] bus_remove_device+0xcc/0x130
Feb 13 18:14:32 localhost kernel: [<c131612f>] ? device_remove_attrs+0x2f/0x90
Feb 13 18:14:32 localhost kernel: [<c1316275>] device_del+0xe5/0x180
Feb 13 18:14:32 localhost kernel: [<c1380326>] usb_disable_device+0x96/0x240 Feb 13 18:14:32 localhost kernel: [<c1379f91>] usb_disconnect+0x91/0x130
Feb 13 18:14:32 localhost kernel: MDV:cdc-acm acm_write_bulk
Feb 13 18:14:32 localhost kernel: [<c137a2c0>] hub_port_connect_change+0xb0/0xa60
Feb 13 18:14:32 localhost kernel: [<c1380f4e>] ? usb_control_msg+0xce/0xe0
Feb 13 18:14:32 localhost kernel: MDV:cdc-acm acm_write_done
Feb 13 18:14:32 localhost kernel: [<c137b296>] hub_events+0x536/0x810
Feb 13 18:14:32 localhost cpcenter: f3c26c00 3672673243 S Co:3:001:0 s 23 01 0010 0001 0000 0
Feb 13 18:14:32 localhost cpcenter: f3c26c00 3672673250 C Co:3:001:0 0 0
Feb 13 18:14:32 localhost kernel: [<c1065bdf>] ? finish_wait+0x4f/0x70
Feb 13 18:14:32 localhost kernel: [<c137b5aa>] hub_thread+0x3a/0x1d0
Feb 13 18:14:32 localhost cpcenter: df2e1840 3672673260 C Bo:3:006:4 -71 0
Feb 13 18:14:32 localhost kernel: [<c1065a70>] ? wake_up_bit+0x30/0x30
Feb 13 18:14:32 localhost kernel: [<c137b570>] ? hub_events+0x810/0x810
Feb 13 18:14:32 localhost kernel: [<c106564c>] kthread+0x7c/0x90
Feb 13 18:14:32 localhost cpcenter: f3c16c80 3672673292 C Bi:3:006:4 -71 0
Feb 13 18:14:32 localhost cpcenter: df2e1d80 3672673453 C Bo:3:006:4 -71 0
Feb 13 18:14:32 localhost cpcenter: f3c16d40 3672673553 C Bi:3:006:4 -71 0
Feb 13 18:14:32 localhost kernel: [<c10655d0>] ? kthread_freezable_should_stop+0x60/0x60
Feb 13 18:14:32 localhost kernel: MDV:cdc-acm read_bulk_callback
Feb 13 18:14:32 localhost kernel: [<c14dedbe>] kernel_thread_helper+0x6/0x10
Feb 13 18:14:32 localhost kernel: MDV 1 acm_read_bulk_callback - urb 3, len 0
Feb 13 18:14:32 localhost kernel: MDV:cdc-acm stop_data_traffic
Feb 13 18:14:32 localhost cpcenter: f3d19500 3672674474 C Ii:3:006:2 -108:64 0
Feb 13 18:14:32 localhost kernel: MDV 2 acm_read_bulk_callback - disconnected
Feb 13 18:14:32 localhost cpcenter: df2e1300 3672674636 C Bo:3:006:4 -71 0
Feb 13 18:14:32 localhost cpcenter: f3c16140 3672674753 C Bi:3:006:4 -71 0
解决方法:
^ @ ^ @ ^ @ ^发送到设备的字符串是内核中终端子系统响应来自设备的传入字节而执行的echo的结果.
日志中的这一行：
Feb 13 18:14:32 localhost cpcenter: df046a80 3672670191 C Bi:3:006:4 0 4 = 00000001
实际上意味着您的设备向计算机发送了4个字节(Bi表示“批量端点,输入”).默认情况下,所有终端设备都启用了echo,因此内核会将这些字节回送给设备,但由于这些字节位于控制字符范围内,因此它们以转义形式回显：^ @ ^ @ ^ @ ^ A.这些回送的字节也在单独的1字节写调用中发送,这对应于后续日志中的1字节批量输出URB.
您需要修复测试程序,以便在尝试与设备通信之前关闭echo和其他tty处理.如果您的测试程序是C/C++,则可以使用cfmakeraw()函数.
该程序可能在Ubuntu中工作只是因为某些其他程序碰巧在测试程序之前触摸端口并更改端口设置以关闭回声.