Re: [gentoo-user] USB device (ATtiny86 w. mcronucleus bootloader) not recognized ?

On 08/07 08:48, R0b0t1 wrote:
> On Mon, Aug 7, 2017 at 4:29 AM, Stefan Mark <mark@××××××××.de> wrote:
> > On Sun, 6 Aug 2017 19:04:09 -0500
> > R0b0t1 <r030t1@×××××.com> wrote:
> >
> >> On Sun, Aug 6, 2017 at 11:50 AM,  <tuxic@××××××.de> wrote:
> >> > When I plug in such a little board into my PC, demesg
> >> > reports:
> >> > [ 1429.834140] usb 7-4: new low-speed USB device number 15 using
> >> > ohci-pci [ 1429.965142] usb 7-4: device descriptor read/64, error
> >> > -62 [ 1430.203151] usb 7-4: device descriptor read/64, error -62
> >> > [ 1430.438161] usb 7-4: new low-speed USB device number 16 using
> >> > ohci-pci [ 1430.569151] usb 7-4: device descriptor read/64, error
> >> > -62 [ 1430.803174] usb 7-4: device descriptor read/64, error -62
> >> > [ 1431.038184] usb 7-4: new low-speed USB device number 17 using
> >> > ohci-pci [ 1431.456157] usb 7-4: device not accepting address 17,
> >> > error -62 [ 1431.582204] usb 7-4: new low-speed USB device number
> >> > 18 using ohci-pci [ 1432.000209] usb 7-4: device not accepting
> >> > address 18, error -62 [ 1432.000244] usb usb7-port4: unable to
> >> > enumerate USB device
> >>
> >> >
> >> > My first thought was: The micronucleus bootloaed is missing or
> >> > is defective...
> >> >
> >> > But plugging in the board into my Android tablet (the tablet runs
> >> > Lollipop and is nothing special at all beside being rooted) via
> >> > an OTG cable and using lsusb after that, it shows
> >> > Bus 001 Device 003 ID 16d0:0753 MCS Digistump DigiSpark
> >> >
> >>
> >> What the dmesg output is saying is that your USB hardware has reported
> >> a communication error to the driver. It is my guess that the ATtiny85
> >> is not meeting the timing requirements for USB.
> >>
> >> Looking at the board there does not seem to be a crystal oscillator
> >> which most people would consider necessary for doing USB
> >> communication. This is an oversight on DigiStump's part and it is very
> >> likely you will not be able to fix the communication issues. You
> >> should contact them and tell them that your computer will not
> >> recognize their device and that you suspect it is because the clock is
> >> too inaccurate.
> >>
> >> >
> >> > What can I do to make this Digispark being correctly recognized?
> >> >
> >> > Thank you VERY much for any help in advance!
> >> >
> >>
> >> Three things:
> >>
> >> 1) Return the one you bought and get a new one. The ATtiny85's
> >> internal oscillator might be at the end of the bell curve but within
> >> manufacturer tolerance, which isn't enough to produce a USB signal
> >> close enough to the specified frequency. Expect the seller to pay for
> >> return shipping.
> >>
> >> 2) You can calibrate the oscillator using instructions in this
> >> application note:
> >> http://www.atmel.com/Images/Atmel-2555-Internal-RC-Oscillator-Calibration-for-tinyAVR-and-megaAVR-Devices_ApplicationNote_AVR053.pdf.
> >> This process still might not get you close enough.
> >>
> >> 3) Add a crystal oscillator to the ATtiny85 and change its fuses to
> >> use the oscillator. You will need to recompile the firmware if the
> >> crystal is a different frequency from the internal oscillator.
> >>
> >> It might work on your phone and not your desktop because of
> >> differences in the USB hardware (your phone's serial decoder in the
> >> USB hardware performs clock recovery but your PC does not) or because
> >> there are multiple things on a USB hub in your PC and the ATtiny85 is
> >> less accurate than those already present devices. Admittedly I'm
> >> surprised it gets most of the way to registering as a device and then
> >> fails, but I don't think the problem is with the drivers or your
> >> kernel.
> > USB uses a variant of non-return-to-zero for clock synchronisation,
> > that should™ take care of timing issues.
> > Actually, using microcontrollers without crystal for soft-usb is fairly
> > common (i have a bunch myself). As far as i understand (but im no
> > expert), trouble usually arises more from the improvised level shifters
> > than timing issues.
> > Anyway, i neither think there is a driver problem, i had a fair bit of
> > the messages myself, usually fixed by fixing the level shifter.
>
> An NRZ signal is part of the reason USB is so finicky. With USB the
> clock has to be within some tolerance of the bus speed (the
> justification being that there are multiple devices on the bus that
> need to read the bus at all times) and this is fairly inflexible. With
> other protocols, like most USART transceivers, the hardware can
> recover the sender's frequency and compensate if it is wrong.
>
> The level shifters might be causing timing problems, seeing as some
> hardware does recognize the ATtiny85 and the levels might be right. It
> seems less likely that a voltage difference would be OK between two
> pieces of hardware to me.
>
> There's a lot of old advice related to microcontrollers that says you
> need to use crystals when you actually don't with modern parts, so I
> think it reasonable that your advice will work. I hope Meino gets back
> to us.
>

I think any modifications on that board is beyond my scope of
abilities regarding soldering a clearly seeing what I doing there...
these SMD thingies are THAT tiny that I fear to inhale that stuff...
than I will be part of the resistance... ;)

I ordered a similiar board yesterday, with a more reasonable setup:
ATmega32u4 and a attached sdcard slot for the flash memory.
The ATmega32u4 has a fully fledged USB 2.0 stack (is it called a "stack"?)
and does not bitbang the whole stuff but "talks USB natively".
I have gathered some hope so far, that this thingy will
a) work with USB < 3.0
b) is more stable and more versatile 

Cheers
Meino