STM32F7 Discovery USB FS CDC Host demo

tau · ‎2016-03-24

Posted on March 24, 2016 at 13:11

Having problems getting this to work. I discovered that optimisation may have been the cause of a couple of errors.

So, if I turn off all optimisation in SW4STM32 (eclipse IDE + gcc toolchain), I can get the F7 disco board to recognise what's plugged in, return VIDs and PIDs ok, and get as far as reporting ''Device not supporting CDC class'' which you can debug on and find that it's failed to init that class ok. I think it's failed to init that class (using USBH_CDC_InterfaceInit) because the USBH_FindInterface is returning 0xFF instead of 0.

If I set USBH_FindInterface to always return 0, then a prolific chipset usb-serial adaptor will get as far as initialising, displaying ''press button to send data'' and then ''sending data ...'' but alas, no data on the scope. An FTDI device plugged in like this will say ''CDC class started'' but not ask to press the button, because the state machine in USBH_Process function is not handling a USBH_NOT_SUPPORTED status in the HOST_REQUEST state.

Anyone got any advice for getting an STM32F7 Discovery USB Host CDC project working?

#cdc #usb #host

tsuneo · ‎2016-03-25

Posted on March 25, 2016 at 13:09

The USB-UART chips of FTDI, Prolific and SiLabs aren't CDC(-ACM) device. These chips expose vendor-specific class, unique for each product. Also, they have their own protocols (Vendor requests). Without knowing their protocols, your effort shouldn't take you anywhere.

To test the CDC host,

Microchip MCP2200 exposes a composite device of CDC-ACM and HID.

Also you may apply an CDC device example on another STM32 board.

To customize the ST's CDC host,

If you would like to implement custom protocol specific to a USB-UART chip,

SiLabs protocol is fair simpler than others. They open their protocol in this appnote.

https://www.silabs.com/Support%20Documents/TechnicalDocs/AN571.pdf

Try it first.

For FTDI,

Unlike SiLabs, FTDI don't open their protocol.

You'll decipher the protocol using USB sniffer log and these source code for Linux.

https://www.intra2net.com/en/developer/libftdi/

http://lxr.free-electrons.com/source/drivers/usb/serial/ftdi_sio.c

or learn from implementation of other MCU

http://processors.wiki.ti.com/index.php/Stellaris_-_USB_Host_FTDI

For Prolific,

1) Descriptors

Prolific descriptors are simplified one of CDC-ACM;

- Single interface with three endpoints (interrupt IN, bulk IN/OUT)

- No extra class-specific descriptor

2) Bulk IN/OUT endpoints

Prolific exchanges just data (without status) over bulk IN/OUT, like CDC-ACM

3) Modem Status

Prolific carries status byte over the interrupt IN pipe, like CDC-ACM

The status byte locates on the ninth byte of ''Notification'' bytes, like CDC-ACM

Its bitmap is same as those of CDC-ACM, just with CTS extension.

http://lxr.free-electrons.com/source/drivers/usb/serial/pl2303.c#L134

134 #define UART_DCD 0x01

135 #define UART_DSR 0x02

136 #define UART_BREAK_ERROR 0x04

137 #define UART_RING 0x08

138 #define UART_FRAME_ERROR 0x10

139 #define UART_PARITY_ERROR 0x20

140 #define UART_OVERRUN_ERROR 0x40

141 #define UART_CTS 0x80

CDC-ACM: UART State Bitmap of SERIAL_STATE notification

D0 bRxCarrier - DCD

D1 bTxCarrier - DSR

D2 bBreak - break

D3 bRingSignal - Ring

D4 bFraming - framing error

D5 bParity - parity error

D6 bOverRun - overrun error

D15..D7 - reserved

4) Vendor specific requests

Prolific requires many vendor read/write at its start up.

Refer to pl2303_startup() on the linux driver.

http://lxr.free-electrons.com/source/drivers/usb/serial/pl2303.c#L220

Tsuneo

tau · ‎2016-03-30

Posted on March 30, 2016 at 14:05

Hello Tsuneo,

thanks for your advice and expertise. I got the CDC Host demo to work on the F7 Disco by using a 429i Disco board as a CDC device. Thanks for the tips on the Prolific driver, might give that a try. Unfortunately I think it's USB sniffer time as I'll be doing it for an FT230X, so I installed WireShark recently. I've been finding this out as I go along, so thanks again for the useful info,

regards,

Turboman