I now have access to a Rock64-4GB (Rock64_V2.0 board); I hope to put FreeBSD on it someday

[Rodney W. Grimes]

> On 2018-Jan-6, at 8:45 AM, Emmanuel Vadot <manu at bidouilliste.com> wrote:
> 
> > On 2018-01-06 17:43, Emmanuel Vadot wrote:
> >> On 2018-01-05 15:45, Mark Linimon wrote:
> >>> On Fri, Jan 05, 2018 at 06:27:41AM -0800, Mark Millard wrote:
> >>>> the early boot baudrate for the console is apparently 1.5Mbit/s
> >>> I've had to use minicom.  That's the only thing that I'm sure supports it.
> >>> mcl
> >> Works fine with tip(1) here using an FDTI usb<->serial, using a
> >> PL2303XA doesn't work (but should based on the datasheet), and my
> >> CP2108 should work but I haven't tested yet.
> > 
> > Also my PL2303XA adapter works on linux using minicom but only for RX, that might be a driver issue.
> 
> I've been using Serial on an old MacOS X laptop.
> I've done more experiments. Here is what I've
> observed. . .
> 
> For a CH340G, Serial did not allow 1500000
> (built-in driver for USB ID 1a86:7523:0254)
> but Serial is being updated to allow it. (I
> have a preliminary release now, so I have
> 1500000 support now.)

I have to seriously laugh at the idea of doing
TTL serial ports at 1.5MHz down unbalanced,
unterminated single end wires.  Just not a
reliable way to communicate.

Hopefully your doing this at 5V, at least
then you have a good noise margin, at 3.3V
you lose another 33% of that.

Also most of these USB/232 adapters have no
way to do flow control, so you better have
a darn big fifo or your host usb stack better
be darn fast at getting data off the chip.

Would be interesting to do a quick Zo calculation
for the setup and put a proper set of termination
resistors on the receive end of the signals to
see how it cleans it up.  Or even look at it with
a good DSO to see how bad and long it rings.

I know that 1.5Mhz is kinda slow, but it is the
edge rate that matters, and TTL drivers have
pretty fast edge rates, 1nS to 3nS is common,
so effectivly your trying to send a 300Mhz 
to 1Ghz signal down a wire, its gona be ugly
at the other end!

> However, there was extensive dropped text from
> sustained output in my limited testing of this
> combination.
> 
> [The CH340G is from the type of serial console
> for the ROCK64 that is sold at pine64.org .]
> 
> I got access to a CP2102 and tried it with Serial
> (again a built-in driver, but for USB ID
> 10c4:ea60:0100). There is far less dropped text,
> although it does happen on occasion for sustained
> serial output.
> 
> I've not tried a FT232R with Serial (AppleUSBFTDI
> driver for USB ID 0403:6001:0600) but could have
> access to do so.
> 
> I've not tried a LP2303X/HX/TA with Serial
> (built-in driver for USB ID 067b:2303:0300) but
> could have access to do so.
> 
> (The device identifications are as reported by
> Serial, both USB ID and "Chip" name.)
> 
> 
> 
> As stands for ubuntu 16.04's top on the ROCK64,
> running via a 70 line window in Serial, I've
> yet to see a screen update that looked completely
> good.
> 
> But most lines for the CP2102 and Serial
> combination look good for each update so far.
> 
> By contrast, the CH340G with Serial had text
> all over the place with few lines ever looking
> good. The bad lines were hard to interpret.
> 
> 
> ===
> Mark Millard
> markmi at dsl-only.net
> 
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-- 
Rod Grimes                                                 rgrimes at freebsd.org