FTDI通用轉USB芯片簡述

FTDI公司的FT2232系列芯片可實現USB與異步串行口RS232/RS485、同步串行總線IIC/SPI/JTAG相互通信，市場占有率，使用普遍。

FTDI芯片有兩種類型的驅動：virtual COM port driver (VCP)和D2xx。VCP就是常用的U轉串COM驅動，實現USB到虛擬串口功能，應用於異步RS232/RS485與USB間通信，linux設備文件為/dev/ttyUSBx；D2XX應用於同步串行總線IIC/SPI/JTAG與USB間通信，整個驅動框架都有FTDI公司提供。

COM驅動

linux支持FTDI公司的VCP驅動需配置內核：

Device Drivers --->

       [*] USB support --->

       <M> USB Serial Converter support --->

                            <M> USB Prolific 2303 Single Port Serial Driver

                            <M> USB FTDI Single Port Serial Driver

Prolific和FTDI是常用的USB轉串口芯片廠商。通用模塊usbserial.ko，prolific公司的模塊pl2303.ko，ftdi公司的模塊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 1-1: new full-speed USB device number 2 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 1-1: pl2303 converter now attached to ttyUSB0

[  289.400405] usb 1-1: USB disconnect, device number 2

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 1-1: new high-speed USB device number 2 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 1-1: Detected FT2232H

[    7.100439] usb 1-1: FTDI USB Serial Device converter now attached to ttyUSB0

[    7.100539] usb 1-1: Detected FT2232H

[    7.100667] usb 1-1: FTDI USB Serial Device converter now attached to ttyUSB1

[   86.423288] usb 1-1: USB disconnect, device number 2

插入USB設備會在/dev/ttyUSBx文件出現，可像操作普通的串口文件/dev/ttySx一樣操作，采用通用termios編程。

D2XX驅動

在linux中VCP和D2XX驅動是不兼容的，當D2XX驅動應用前應卸載VCP驅動模塊：

sudo rmmod ftdi_sio

sudo rmmod usbserial

實際測試中采用D2XX驅動時系統會自動卸載VCP驅動。

D2XX驅動協議棧如下圖，D2XX驅動libftd2xx.tar.gz可在如下頁面下載：https://www.ftdichip.com/Drivers/D2XX.htm，或者直接在系統下apt安裝（可能需要libusb-dev）：

apt install libftdi-dev

在D2XX驅動之上是libmpsse，即MPSSE庫。Multi Protocol Synchronous Serial Engine(MPSSE)是一個通用的同步總線如I2C、SPI或JTAG通信庫，用於FT2232D、FT2232H、FT4232H和FT232H芯片通過USB與PC或ARM通信。MPSSE基於D2XX設計。

 

D2XX應用

lora gateway就應用了D2XX驅動，將SPI接口轉化為U口與主服務器（X86或ARM）通信，開源庫：https://github.com/yuxi-o/RAK833-LoRaGateway-RPi或https://github.com/Lora-net/lora_gateway.git。

 

參考：

1． https://www.ftdichip.com/Support/Documents/AppNotes.htm

2． FTDI FT2232H在嵌入式教學中的應用

3． linux內核支持U-disk和U轉串

4． FTDI Drivers Installation Guide for Linux

5． User Guide For LibMPSSE-SPI