I2C UART to Linux

Hi,

Our company is evaluating to build a custom Arduino shield for datalogging (All protocols that needs level-converters). We want to use multiple different SoC`s, and communicate with those via UART to Linux application. I have done research on how to communicate with the Yocto Linux via SPI bus to map multiple tty`s to SoC`s on our shield, and I have read that the MRAA library is handling this (UART Class). I have found i.e this chip that supports up to two UARTS per chip via SPI bus:

https://www.nxp.com/docs/en/brochure/75015676.pdf

Does anyone have any experience or an opinion on how this is done? I dont have experience with SPI or MRAA. Does nxp have to deliver some code for me to map SPI-UART to Linux/mraa-UART?  Or is this a hopeless project with bytebuffers and serial handling..

Best Regards

Benjamin Kruger

There are basically two paths:

• use mraa as SPI programming interface to write a simple user-space tty driver (custom API) for the selected chip
• select a UART-SPI chip with a preexisting Linux kernel driver (or write that driver yourself) and wire up the device via ACPI rules (similar to the ACPI fixups we currently ship)

The second option might be more complicated from the configuration point of view, but it would give you native Linux ttys while the first one would require the application to use a custom API.

OK,

Seems like option 2 is the way to do it. I found this MAX3100 chip that seems to be supported:

https://cateee.net/lkddb/web-lkddb/SERIAL_MAX3100.html

I guess I will have to look into this ACPI configuration then. For everyone else that find this interesting; I will post my ACPI config for other to use later If I ever get it working 

/Ben

Hi Benjamin,

I work on a similar shield with SPI and serial communication.

But I use a simple solution for that.

My question to you:

1. How many serial ports do you need and what is the maximum serial communication speed ?

2. On IOT2000 side do you provide a library or a full program to your customer ?

3. How do you select on which serial port do you communicate on your library ?

Ocean

Hi,

Very good questions:

1. My plans is for three chips, and they need one UART each. Transmission speeds AFAIK is 14.4k for now.

2. Full program. I am logging energy data with OpenMUC. (www.openmuc.org)

3. This is a very relevant question. I do not have a solution yet, but from toughts from the top of my head, I have a plan on that the SS (Slave Select) will make the kernel via ACPI or something else (far shot) to link specific tty`s to the different SPI->UART ICs, since we design the shield ourself. This is part of the journy ahead:)

Do you have any answers to your own questions, in particular no 3? Do you have experience or plans on which chip you are looking for, and if there is existing code to implement/start from?

/Ben

Ben1902

I guess I will have to look into this ACPI configuration then. For everyone else that find this interesting; I will post my ACPI config for other to use later If I ever get it working 

This might be helpful, at least as reference: https://github.com/westeri/meta-acpi/. Mika and Andy also answered a couple of questions about it while I was working on the IOT2000 ACPI changes.

Jan,

One more thing. It seems that on galileo gen 2, pin 2 & 3 is also an uart? Is this valid even for IOT2000, or is this in fact the console UART?

https://communities.intel.com/thread/55920

/Ben

Hi Benjamin,

in energy systems are mostly RS485 communication system used.

Its a asynchronous system. You must switch rx and tx for communication.

And that is very time critical to implement. For example Modbus-RTU or DNP3 can you implement with software. But other time critical protocols profibus or canbus for example are not possible to implement with software.

Please look in your MySupport->Personal Message->Inbox for help.

Ocean

jan-k

Yes, the 2020 has 2 on-chip UARTs and the 2040 2 extra ones via the Exar PCI device. Of the 2 on-chip UARTs, one (ttyS1) is preconfigured to act as serial console. But that can be changed in a custom image, of course.

Hi,

In the Galileo Gen2, there is possible to route the second UART between either the onboard pins(X14@IOT2000) or pin D2 & D3. Is this possible to mux on the IOT2000 as well? Say if I ditch the console and want two UARTS to my shield. Ref Galileo Gen 2 block diagram attached (UART 1).

/Ben