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. -- B.Walter <be...@bwct.de> http://www.bwct.de Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.
