USB CDC on STM32F746 with ChibiOS 16.1

[Korken]

Okey, if I changed to OTG1 instead of OTG2 it started working while having the external 1.5k resistor.
But when I removed the external 1.5k resistor it stopped enumerating again.

What is it that I have to change to enable the internal 1.5k Pull-up for OTG1?

[Giovanni]

OTG2 can have an external PHY or not have it, the board configuration differs.

The STM32F7-Discovery has the external PHY for example.

Giovanni

[Korken]

Yes, but the USB FS that I am using should have an internal 1.5k pull-up resistor?

I checked the RM for the bit:

Code: Select all

/**
 * @brief   Connects the USB device.
 *
 * @api
 */
#if !defined(usb_lld_connect_bus)
#define usb_lld_connect_bus(usbp) (STM32_USB->BCDR |= USB_BCDR_DPPU)
#endif

But it does not exist, do you know which it is? I cannot seem to find it.

[Giovanni]

The pull-up is internal and the driver works on the Discovery board. If the enumeration starts then the resistor is working or plugging the device would not even be detected by host.

Giovanni

[Korken]

The thing is that the USB resistor is not working.
If I add an external resistor it works.

I checked the stm32f746x.h for the USB resistor pull-up bit for USB FS (OTG1) but it does not exist.
I am starting to believe that it is not there. I am though not familiar with the USB part of the RM, so I cannot find anything about the internal 1.5k when using USB FS.

Are you sure it is there?

[Korken]

Okey, I now found what gave the intermitent nature of the error, one of the 22 ohm resistors where broken and soldiering the big resistor made a connection.
When it was removed to try again, the resistor was broken. Now replaced it seems to work as it should.

[Korken]

Final question on the USB.

When opening the USB serial port from the PC the board Halts with the error:

chSysHalt (reason=0x8008c84 <__func__.9659> "obqReleaseEmptyBufferI") at ./ChibiOS/os/rt/src/chsys.c:184

and I get the error on the PC side:

cdc_acm 1-2:1.0: failed to set dtr/rts

It seems that something is not implemented that has to do with the DTR/RTS signals that I am missing, does anyone know what it is?
I am unable to find it in any example code for the CDC.

Thanks!

[Giovanni]

Probably an unimplemented CDC message, the CDC driver only implement a minium of them, you need to provide handlers for the others.

I cannot explain that error however, post a stack trace.

Giovanni

[Korken]

I see, is there a way to see which one is missing?
Sorry, but USB is not my strong side - I only want a "simple" USB serial port

[Giovanni]

The default handler is sduRequestsHook(), place a breakpoint there and you will know why it fails (return false).

Giovanni