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USBH CDC ACM Virtual Com Port Question

hojin kim

In Keil's Run Time Environment

I will only use USB Port
I use it as virtual com.

When I coding USB Host Virtual com
as usbh cdc acm, usart port included, why??

//////////////////////////
extern ARM_DRIVER_USART Driver_USART9;
#define ptrUART_USB (&Driver_USART9)
////////////////////////

In keil's "manage run time environment" configure
mcu : stm32f207vc
CMSIS : core
RTOS : Keil RTX
CMSIS Driver : USART(API) : CDC, USART
USB Host(API) : Full Speed
Device : CStartup, classic
Device : common,Cortex,DMA,GPIO,RCC
USB : Host :CDC

  • 0 Arm Employee Badge

    Hi Hojin,

    This is just a implementation that provides CMSIS USART driver to communicate with CDC device.
    Index 9 is selected not to clash with any hardware USARTs that a chip has. You can configure the index differently by providing define USART_CDC_DRV0_NUM to the USART_CDC_ACM.c driver.

    You can use USBH CDC without CMSIS USART driver for CDC communicated directly by using USBH functions for example USBH_CDC_ACM_Send/USBH_CDC_ACM_Receive.

  • 0 in reply to Milorad Cvjetkovic

    Hi Milorad Cvjetkovic

    Thanks for your reply

    //////////////////////////////////////////////////////////

    I use sample program "">www.keil.com/.../host_cdc_tutorial.html"

    My problem is "USBH_CDC_ACM_GetDeviceStatus" function is not working,
    May be can't detect usb device connection

    How can I fix
    When I use keil debugger, i can't debug into.

    //////////////////////////////////////////////////////////

    In these sample i don't use MCBSTM32F400 board and STM32F407IGHx mcu
    I use stm32f207vct mcu and my own board equipped with USB

    When I make cdc host and cdc device program using CubeMX,
    connect board each other via USB port using my board

    usb detection,
    send data and receive : USBH_CDC_Transmit,USBH_CDC_Receive, CDC_Transmit_FS function
    working very good

    //////////////////////////////////////////////////////////

  • 0 Arm Employee Badge in reply to hojin kim

    Hi Hojin,

    What is your CDC device that you want to communicate to with USB Host?
    Is it perhaps some USB Mobile Network adapter?

  • 0 in reply to Milorad Cvjetkovic

    Hi Milorad Cvjetkovic

    My ultimate goal is that my device can communicate with USB device that has vendor specific class but protocol of USB device is a serial, text-based protocol

    that USB device only require but vendor specific class.
    8 data bits;
    no parity bits;
    1 stop bit;
    19200 baud rate.

    Does this "USBH CDC ACM Virtual Com Example" not support it ???
    Do I must know if USB has vendor specific class protocol ?

    Thanks.

  • 0 Arm Employee Badge in reply to hojin kim

    Hi Hojin,

    you should take a look at following documentation page: www.keil.com/.../host_cust_tutorial.html

    it explains how USB Host is used with Prolific PL2303 USB-to-UART dongle, that device also uses Vendor Specific class.

    And yes, you can not use CDC for communicating with such a device as Vendor Specific means it is not standardized so you need to know the protocol, CDC device is standardized.