项目上须要用到蓝莓派CM4，驱动XR2121VV14141414芯片，蓝莓派版本是2021-05-07-raspios-buster-armhf-full，XR2121VV14141414是USB转4路并口芯片。
当将XR2121VV14141414联接蓝莓派的USB口后，会手动辨识成ttyACM0、ttyACM1、ttyACM2、ttyACM3，此时打开任意并口linux usb 转串口驱动，并进行读写操作linux usb 转串口驱动，可以成功，但当发送到几十次后才会卡主，再也没法读写。并且经过检测发觉实际数据并没有发出来，TX，RX上均没有电平变化。出现这个问题的缘由是猕猴桃派外置的驱动是cdc-acm，实际未能驱动XR2121VV14141414芯片，须要更新驱动。
从官方网站上找到驱动linux vi ，按照自己板子的内核版本来选择驱动版本，可以用uname-a来查看内核版本号，例如我自己的板子
可以看见我的是5.10版本，须要驱动支持3.6以上版本即可
也就是这一条，下载然后放在板子上，直接解压，并步入板子，用make指令编译，即可得到驱动包xr_usb_serial_common.ko。此时还不能直接加载驱动，由于系统本身还有cdc-acm驱动，须要卸载掉以后才行，因而须要先执行卸载，再加载
sudormmodcdc-acm
sudoinsmod./xr_usb_serial_common.ko
此时，查看dev下设备，即可见到ttyXRUSB0、ttyXRUSB1、ttyXRUSB2、ttyXRUSB3这4个设备，这时就可以进行正常收发操作。
事情到旁边又发生了变化，由于覆盆子派更新了系统，在21年11月以后，发布的2021-10-30-raspios-bullseye-armhf-full版本，内核弄成了5.15，此时再重复以上操作，还会出错，首先是步入驱动文件进行make操作时，会提示找不到build文件
pi@raspberrypi:/mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak $ make
make -C /lib/modules/5.15.32-v8+/build M=/mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak
make[1]: *** /lib/modules/5.15.32-v8+/build: No such file or directory. Stop.
make: *** [Makefile:9: all] Error 2
此时须要加载kernel的build文件，使用以下
sudoaptinstallraspberrypi-kernel-headers
pi@raspberrypi:/mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak $ sudo apt install raspberrypi-kernel-headers
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following NEW packages will be installed:
raspberrypi-kernel-headers
0 upgraded, 1 newly installed, 0 to remove and 14 not upgraded.
Need to get 9675 kB of archives.
After this operation, 60.6 MB of additional disk space will be used.
Get:1 //archive.raspberrypi.org/debian bullseye/main arm64 raspberrypi-kernel-headers arm64 1:1.20220331-1 [9675 kB]
Fetched 9675 kB in 6s (1602 kB/s)
apt-listchanges: Can't set locale; make sure $LC_* and $LANG are correct!
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
LANGUAGE = "en_US.UTF-8",
LC_ALL = "en_US.UTF-8",
LANG = "en_US.UTF-8"
are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
locale: Cannot set LC_CTYPE to default locale: No such file or directory
locale: Cannot set LC_MESSAGES to default locale: No such file or directory
locale: Cannot set LC_ALL to default locale: No such file or directory
Selecting previously unselected package raspberrypi-kernel-headers.
(Reading database ... 99103 files and directories currently installed.)
Preparing to unpack .../raspberrypi-kernel-headers_1%3a1.20220331-1_arm64.deb ...
Unpacking raspberrypi-kernel-headers (1:1.20220331-1) ...
Setting up raspberrypi-kernel-headers (1:1.20220331-1) ...
pi@raspberrypi:/mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak $
执行完成后，/lib/modules/5.15.32-v8+/路径下即可见到build文件夹，此时重新make编译驱动，会发觉编译报错
pi@raspberrypi:/mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak $ sudo make
make -C /lib/modules/5.15.32-v8+/build M=/mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak
make[1]: Entering directory '/usr/src/linux-headers-5.15.32-v8+'
CC [M] /mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak/xr_usb_serial_common.o
/mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak/xr_usb_serial_common.c:2019:17: error: initialization of 'unsigned int (*)(struct tty_struct *)' from incompatible pointer type 'int (*)(struct tty_struct *)' [-Werror=incompatible-pointer-types]
2019 | .write_room = xr_usb_serial_tty_write_room,
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak/xr_usb_serial_common.c:2019:17: note: (near initialization for 'xr_usb_serial_ops.write_room')
/mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak/xr_usb_serial_common.c:2026:21: error: initialization of 'unsigned int (*)(struct tty_struct *)' from incompatible pointer type 'int (*)(struct tty_struct *)' [-Werror=incompatible-pointer-types]
2026 | .chars_in_buffer = xr_usb_serial_tty_chars_in_buffer,
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak/xr_usb_serial_common.c:2026:21: note: (near initialization for 'xr_usb_serial_ops.chars_in_buffer')
/mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak/xr_usb_serial_common.c: In function 'xr_usb_serial_init':
/mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak/xr_usb_serial_common.c:2040:29: error: implicit declaration of function 'alloc_tty_driver' [-Werror=implicit-function-declaration]
2040 | xr_usb_serial_tty_driver = alloc_tty_driver(XR_USB_SERIAL_TTY_MINORS);
| ^~~~~~~~~~~~~~~~
/mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak/xr_usb_serial_common.c:2040:27: warning: assignment to 'struct tty_driver *' from 'int' makes pointer from integer without a cast [-Wint-conversion]
2040 | xr_usb_serial_tty_driver = alloc_tty_driver(XR_USB_SERIAL_TTY_MINORS);
| ^
/mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak/xr_usb_serial_common.c:2057:3: error: implicit declaration of function 'put_tty_driver' [-Werror=implicit-function-declaration]
2057 | put_tty_driver(xr_usb_serial_tty_driver);
| ^~~~~~~~~~~~~~
cc1: some warnings being treated as errors
make[2]: *** [scripts/Makefile.build:277: /mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak/xr_usb_serial_common.o] Error 1
make[1]: *** [Makefile:1868: /mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak] Error 2
make[1]: Leaving directory '/usr/src/linux-headers-5.15.32-v8+'
make: *** [Makefile:9: all] Error 2
pi@raspberrypi:/mnt/Work/driver_64/xr_usb_serial_common_lnx-3.6-and-newer-pak $
这个报错是由于系统内核变化了，5.15版本之后不支持put_tty_driver和alloc_tty_driver，早已更换成tty_driver_kref_put和tty_alloc_driver，所以要步入代码文件进行更改，另外xr_usb_serial_tty_write_room函数和xr_usb_serial_tty_chars_in_buffer函数也须要更改，把定义函数时的int改为unsignedint，更改完成后（xr2121vv14141414驱动，支持3.6-5.15版本）即可正常编译linux开发培训，得到ko文件，前面的操作就跟上面一样了。
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