Hi Bernd, I develop a product for a customer some years ago using the SAMD21 with USB CDC/ACM and it worked fine. It was based on NuttX 7.27
The board was using a 8MHz crystal. BR, Alan On 12/15/20, Bernd Walter <ti...@cicely7.cicely.de> wrote: > On Tue, Dec 15, 2020 at 07:28:38PM +0100, Bernd Walter wrote: >> Ich have some older boards with an at91samd21j18, but without xtal. >> I use them with USB and like to convert the code wo NuttX. >> So far I'd used the Atmel-ASF to setup the clock and for USB stack >> under FreeRTOS. >> However, after reinspecting I hadn't used the correct clock setup, >> which would be using the DFLL with USB SOF as reference clock. >> Instead I used the internal 32kHz RC and rasied it with the DFLL. >> Nonetheless it worked fine. >> >> On another board I already noticed that something is wrong with the >> DFLL under NuttX. >> It was a board with XTAL, on which I initially hadn't used the XTAL >> and instead raised the internal 8MHz with the DFLL. >> On some boards I couldn't use the UART at 115200 bps because the >> clock was off. >> This was unexpected, since the 8MHz is claimed to be precise. >> However, what was more unexpected that I have had exactly the same >> offset by using an external 16MHz xtal. >> In the end I dropped the DFLL and used the DPLL instead, which worked >> fine. >> >> I modified the clock init code to support USB clock recovery and >> in didn't work at first. >> After modifying some other things I got my 48MHz, at least USB >> came up. >> Now I have another problem. >> USB isn't stable. >> I use ACM-TTY and my main routine only loops on printing a counter >> and short sleep. >> After 1-2minutes USB dies off. >> Now I wonder if this is still something clock related or if there >> is something else wrong with USB on the SAMD21. >> >> I will do further tests - I have some boards with a 16MHz xtal and >> USB connector. >> I also never checked if the DFLL has locked or not. >> But at this point I'm also open for other peoples experiences. > > A followup on that. > I'm now running on a similar board, which has a 16MHz xtal. > GCLK0/USB is running of the DPLL and I still have the problem that USB > locks up after a while. > I don't think this is clock related anymore, but I'm also not sure if > this is even USB as such, although my code is faily simple. > > I can do a pull request on my DFLL changes, which I think are the > correct thing to do. > There are some errata related bug workarounds and fixes a wrong > initialisation order. > And also adds support for USB clock recovery. > > -- > B.Walter <be...@bwct.de> http://www.bwct.de > Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm. >
