FTDI公司的FT2232系列芯片可实现USB与异步串行口RS232/RS485、同步串行总线IIC/SPI/JTAG相互通信，市场占有率，使用普遍。
FTDI芯片有两种类型的驱动：virtual COM port driver (VCP)和D2xx。VCP就是常用的U转串COM驱动，实现USB到虚拟串口功能，应用于异步RS232/RS485与USB间通信，linux设备文件为/dev/ttyUSBx；D2XX应用于同步串行总线IIC/SPI/JTAG与USB间通信，整个驱动框架都有FTDI公司提供。
COM驱动
linux支持FTDI公司的VCP驱动需配置内核：
Device Drivers --->
[*] USB support --->
<M> USB Serial Converter support --->
<M> USB Prolific Single Port Serial Driver
<M> USB FTDI Single Port Serial DriverProlific和FTDI是常用的USB转串口芯片厂商。通用模块usbserial.ko，prolific公司的模块pl2303.ko，ftdi公司的模块ftdi_sio.ko
[ 1.771996] usbcore: registered new interface driver usbfs [ 1.777600] usbcore: registered new interface driver hub [ 1.782975] usbcore: registered new device driver usb [ 3.227325] usbcore: registered new interface driver usb-storage [ 3.331190] usbcore: registered new interface driver bcm203x [ 3.336872] usbcore: registered new interface driver bfusb [ 3.342381] usbcore: registered new interface driver btusb [ 3.347893] usbcore: registered new interface driver ath3k [ 3.496381] usbcore: registered new interface driver usbhid [ 3.501958] usbhid: USB HID core driver [ 58.132670] usb -: new full-speed USB device number using xhci-hcd [ 58.314580] usbcore: registered new interface driver usbserial [ 58.316675] usbcore: registered new interface driver pl2303 [ 58.316707] usbserial: USB Serial support registered for pl2303 [ 58.317386] usb -: pl2303 converter now attached to ttyUSB0 [ 289.400405] usb -: USB disconnect, device number
或
[ 1.774779] usbcore: registered new interface driver usbfs [ 1.780377] usbcore: registered new interface driver hub [ 1.785752] usbcore: registered new device driver usb [ 3.230535] usbcore: registered new interface driver usb-storage [ 3.334244] usbcore: registered new interface driver bcm203x [ 3.339930] usbcore: registered new interface driver bfusb [ 3.345439] usbcore: registered new interface driver btusb [ 3.350951] usbcore: registered new interface driver ath3k [ 3.495753] usbcore: registered new interface driver usbhid [ 3.501362] usbhid: USB HID core driver [ 3.643788] usb -: new high-speed USB device number using xhci-hcd [ 7.070296] usbcore: registered new interface driver usbserial [ 7.099899] usbcore: registered new interface driver ftdi_sio [ 7.099925] usbserial: USB Serial support registered for FTDI USB Serial Device [ 7.100046] usb -: Detected FT2232H [ 7.100439] usb -: FTDI USB Serial Device converter now attached to ttyUSB0 [ 7.100539] usb -: Detected FT2232H [ 7.100667] usb -: FTDI USB Serial Device converter now attached to ttyUSB1 [ 86.423288] usb -: USB disconnect, device number
插入USB设备会在/dev/ttyUSBx文件出现，可像操作普通的串口文件/dev/ttySx一样操作，采用通用termios编程。
D2XX驱动
在linux中VCP和D2XX驱动是不兼容的，当D2XX驱动应用前应卸载VCP驱动模块：
sudo rmmod ftdi_sio
sudo rmmod usbserial
实际测试中采用D2XX驱动时系统会自动卸载VCP驱动。
D2XX驱动协议栈如下图，D2XX驱动libftd2xx.tar.gz可在如下页面下载：https://www.ftdichip.com/Drivers/D2XX.htm，或者直接在系统下apt安装（可能需要libusb-dev）：
apt install libftdi-dev
在D2XX驱动之上是libmpsse，即MPSSE库。Multi Protocol Synchronous Serial Engine(MPSSE)是一个通用的同步总线如I2C、SPI或JTAG通信库，用于FT2232D、FT2232H、FT4232H和FT232H芯片通过USB与PC或ARM通信。MPSSE基于D2XX设计。
D2XX应用
lora gateway就应用了D2XX驱动，将SPI接口转化为U口与主服务器（X86或ARM）通信，开源库：https://github.com/yuxi-o/RAK833-LoRaGateway-RPi或https://github.com/Lora-net/lora_gateway.git。
参考：
1． https://www.ftdichip.com/Support/Documents/AppNotes.htm