Re: usb CH9102 serial chip

> On 17 Feb 2022, at 20:04, Daniel Braniss <danny@cs.huji.ac.il> wrote:
>> On 17 Feb 2022, at 11:30, Daniel O'Connor <darius@dons.net.au> wrote:
>> 
>>> On 17 Feb 2022, at 19:50, Daniel Braniss <danny@cs.huji.ac.il> wrote:
>>> 
>>>> If that is the case then the chip/driver are working fine since that requires bidirectional communication etc..
>>>> 
>>> 
>>> but that works only if I power up the board while pressing a button, then it also appears as /dev/ttyU0, and
>>> so then I can flash, after reset, the device is gone and there are errors ( BTW, the flashed image workes):
>>> 
>>> Feb 17 09:46:59 pampero kernel: usbd_setup_device_desc: getting device descriptor at addr 4 failed, USB_ERR_IOERROR
>>> Feb 17 09:47:00 pampero kernel: usbd_req_re_enumerate: addr=4, set address failed! (USB_ERR_IOERROR, ignored)
>> 
>> What sort of dev board is it?
> 	m5 stamp C3U
> https://shop.m5stack.com/products/m5stamp-c3u-mate-with-pin-headers?_pos=2&_sid=3df9b5f0d&_ss=r&variant=42341016633601

According to the docs the 'U' variant doesn't have a serial chip on it. If you look at the schematic the USB +/- pins go straight to the MCU.

I suspect it has a boot loader which emulates the CH9102, when your code is running it is whatever that does with the USB port, so if there is a bug or whatever then it will exhibit weird behaviour.

--
Daniel O'Connor
"The nice thing about standards is that there
are so many of them to choose from."
 -- Andrew Tanenbaum