Circuits.UART.enumerate returns nothing %{"ttyAMA0" => %{}, "ttyS0" => %{}}

[shahryarjb]

Setup

• Version: (if not latest, please try upgrading) {:circuits_uart, "~> 1.4"}
• OS: OSX
• Platform: Raspberry Pi 4

Expected Behavior

I install circuits_uart on my Nerves project and after burning on it. I connect to my nerves and run this function: Circuits.UART.enumerate

iex(5)> Circuits.UART.enumerate
%{"ttyAMA0" => %{}, "ttyS0" => %{}}
iex(6)> Circuits.UART.enumerate
%{"ttyAMA0" => %{}, "ttyS0" => %{}}
iex(7)> {:ok, pid} = Circuits.UART.start_link
{:ok, #PID<0.1130.0>}
iex(8)> Circuits.UART.enumerate
%{"ttyAMA0" => %{}, "ttyS0" => %{}}

but it can not find anything, although I connected 3 different USB to my Raspberry Pi 4:

for example: flash drive

iex(52)> Circuits.UART.open(uart, "ttyS0", speed: 9600,active: true)
:ok
iex(53)> Circuits.UART.write(uart, "Hello there\r\n")
:ok
iex(54)> Circuits.UART.read(uart, 60000)
{:error, :einval}

Thank you

[fhunleth]

Nerves doesn't ship with the device drivers for the USB serial cables that you're using. It has drivers for cables with these chips in them: https://github.com/nerves-project/nerves_system_rpi4/blob/main/linux-5.10.defconfig#L466-L469.

"ttyS0" goes to the GPIO header's UART pins. "ttyAMA0" goes to the Bluetooth module on the board. It looks like "ttyS0" is working for you. You specified active mode, so everything sent over the serial port will be turned into an Elixir message. Run flush to get those. UART.read/2 returns an error since you specified active mode.

[shahryarjb]

Thank you, @fhunleth, it is hard to understand for me, and I am very sorry I am trying to figure out how it works.

iex(1)> {:ok, uart} = Circuits.UART.start_link
{:ok, #PID<0.1124.0>}
iex(2)> Circuits.UART.open(uart, "ttyS0", speed: 9600,active: true)
:ok
iex(3)> Circuits.UART.write(uart, "Hello there\r\n")
:ok
iex(4)> flush
:ok
iex(5)> Circuits.UART.read(uart, 60000)
{:error, :einval}

I saw many topics and when they run flush they could see the outputs, but I just got a :ok atom. I just need something to test and see result to continue with what I receive. Furthermore, I changed active: true to flase and run Circuits.UART.read(uart, 60000) it took a 2 or 3 min to show {:ok, ""}

iex(6)> Circuits.UART.open(uart, "ttyS0", speed: 9600,active: false)
:ok
iex(7)> Circuits.UART.write(uart, "Hello there\r\n")
:ok
iex(8)> flush
:ok
iex(9)> Circuits.UART.read(uart, 60000)
{:ok, ""}

Again I am very sorry, I just want to create an open-source project for analysing cars Which is based on a thesis. Thank you

[fhunleth]

Nothing was received on the UART. I'm not sure what you're expecting to be received, so maybe it's working just fine?

[fhunleth]

Circuits.UART also works on MacOS, so you could try it out there as well.

[shahryarjb]

@fhunleth would you mind suggesting me a device or something exists in home to test its USB? I do not know how to send a file or something to my Raspberry Pi and get this with your library, it shows me {:ok, ""} because no device is connected to it.

If I find a device and connect with its USB, I think I can find a way to connect to a car. I tried my mobile, but I didn't know how to send a file or receive it.

[fhunleth]

Can you connect a wire from the UART's TX pin to the UART's RX pin? Then you can send strings to yourself.

[shahryarjb]

I think I can't, I do not know event these name ;), but I relay want to say thank you for all your efforts. I should find a device to connect.

I have a question, when we want to write or receive, we should know some specialized String like AT, AC to connect a device, for example every device needs? And every company has the own String or Integer?

For example:

If I run Circuits.UART.write(uart, "AT"), It gives me back the number of passengers, for example?!! If yes, what should I search about it? What is this keyword?

[fhunleth]

I'm going to close this.

Before you ask more questions here, could you spend some time reading up on serial ports and serial communication? I think this will help quite a bit.

[shahryarjb]

@fhunleth, yes sure. May you suggest me a reference?

Before taking your time, I want to prepare a car ECU and OBD cable and test them, because I think I can't test it with my mobile or some devices exist in my home.

Thank you very much