[J-core] Checking in.

wjones at wdj-consulting.com wjones at wdj-consulting.com
Fri Dec 6 20:26:00 UTC 2019


>In the existing bitstream? One. The USB-A charge connection thingy has a 
>serial
port on it, which the kernel serial console defaults to. (I.E. plug it into 
a
laptop or powered hub and it's both the power source and a serial data 
connection.)
In my setup, it's _probably_ not going to be feasible to use a serial port 
that's shared with the power connection. I plan to plug the TurtleBoard 
directly into an outlet. What is the current draw of the TurtleBoard under 
load if you know? I can _try_ it and see what happens, of course.

>Here's an old post about modifying the bitstream to put serial ports on the 
>GPIO
pins:
http://lists.j-core.org/pipermail/j-core/2016-April/000070.html

This is very good to know, I'm probably going to have to go this route and 
redirect the kernel console to this port.

>We have a TODO item to hook up DMA to the serial port in the kernel, but 
>haven't
done it yet.
Not a big deal, even on my most powerful SBC (Tinker Board), DMA on the 
serial port doesn't work :P. I'll manage without it.

>I could add a getty to toybox that does it, I just didn't know there was 
>demand?
I would appreciate that; I know my use case is niche, but PPP has actually 
saved me a number of times where the a serial line (combined with proxy ARP) 
is the only convenient way to get Internet access. A multiplexing getty, 
_once it's set up_ :), makes debugging issues _a lot_ easier.


-----Original Message----- 
From: Rob Landley
Sent: Friday, December 06, 2019 3:09 PM
To: wjones at wdj-consulting.com
Cc: j-core at lists.j-core.org
Subject: Re: [J-core] Checking in.

On 12/6/19 6:48 AM, wjones at wdj-consulting.com wrote:
> While this is on my mind...
>
> How many UARTs are available on TurtleBoard?

In the existing bitstream? One. The USB-A charge connection thingy has a 
serial
port on it, which the kernel serial console defaults to. (I.E. plug it into 
a
laptop or powered hub and it's both the power source and a serial data 
connection.)

It's got 4 standard USB ports, each of which can have a serial adapter 
plugged
into it, or add a USB hub and I think you can have 127 devices?

Here's an old post about modifying the bitstream to put serial ports on the 
GPIO
pins:

  http://lists.j-core.org/pipermail/j-core/2016-April/000070.html

You might need an i2c to uart converter chip depending on what electrical
signals you want to hook it to at the other end, but Jeff didn't use one 
when he
slapped one of those together on a numato board that had a bad serial 
connector
so he rebuilt the bitstream for a demo an hour beforehand. (He just stuck 
wires
on the pins and it worked for him? You need the stty command to disable
hardaware flow control, but you needed that on numato anyway. Unless you 
wire up
the 4 pin version in the bitstream...)

> I don't actually plan to use the
> Ethernet on my TurtleBoard. Instead, I plan use PPP to connect it to the
> Internet (it'll connect a UART to a wifi-enabled board's secondary UART). 
> If
> there is only room for one UART plus Ethernet, is it possible to 
> accommodate my
> requirement and replace Ethernet with a second UART in the bitstream?

UARTs are tiny and even the _small_ turtle is LX25: that's almost 3 times 
the
size of the LX9 in the numato board. And the LX45 version is 5 times the 
size of
the LX9.

We have a TODO item to hook up DMA to the serial port in the kernel, but 
haven't
done it yet.

> The (Net)BSD getty is smart enough to multiplex pppd and login when only a
> single UART is available, but I don't believe any Linux getty 
> implementations
> have this feature...

I could add a getty to toybox that does it, I just didn't know there was 
demand?

Jeff flew to Japan yesterday and I haven't heard from him since (probably
collapsed as soon as he got there, 10 hour time difference from Ontario and 
he
flew out after noon), but he's the guy to ask about the ship schedule. The
hardware's here, the blocker is us fleshing out the bitstream and doing the
packaging and documentation and such...

Rob

--
William D. Jones
wjones at wdj-consulting.com 



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