[J-core] Checking in.

Rob Landley rob at landley.net
Fri Dec 6 20:09:27 UTC 2019

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


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...


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