Raspberry UART

[luiHS]

 
Hi.

I need to make a program for serial port communications with the Raspberry. I've been reading that the Raspberry has two UARTs; the Mini UART and the PL011.

1.- The mini UART (/dev/ttyS0) is dependent on the frequency of the core VPU, which can vary according to the processor load, and therefore could be unstable and fail.
2.- On the other hand, using the PL011 (/dev/ttyAMA0) implies having to disable Bluetooth.

What UART do you usually use with the Raspberry that is not a problem ?, is to communicate at 115200 baud with a Kinetis MK66 microcontroller, I have doubts if it is reliable to use the mini UART.

Regards
 

[ebclr]

You can attach a USB 232 cable on the USB port, Will be the 3rd option

[Siwastaja]

On Raspi3, I have used /dev/serial0 reliably, I think the key was to set force_turbo in /boot/config.txt, which removes CPU frequency throttling, of course increasing power dissipation, but on Raspi3, this won't cause thermal issues unless you have a tight, closed box with very poor cooling.

Don't know how it's on Raspi4, though.

[GeorgeOfTheJungle]

1.- The mini UART (/dev/ttyS0) is dependent on the frequency of the core VPU, which can vary according to the processor load, and therefore could be unstable and fail.
2.- On the other hand, using the PL011 (/dev/ttyAMA0) implies having to disable Bluetooth.

Really? Wow, the list of RPi hardware issues is a never ending story. Use a good SBC, an Orange Pi PC is not only better but also cheaper.

https://www.aliexpress.com/item/32448079125.html

[johnkenyon]

You could attach a UART to the I2C or SPI pins.

Do a search for a "i2c UART" and/or "SPI UART".
This yields things like the MAX3107 (single serial port with 128byte FIFO).
I'm sure I've seen single chip 4 and 8 port devices.

Another place to look is in the Linux kernel source.
Looking at /usr/src/linux/drivers/tty/serial/Kconfig revealed support (from at least 4.4.x onwards) for the following:

SERIAL_MAX310X
Supported ICs are MAX3107, MAX3108, MAX3109, MAX14830.
Each IC contains 128 words each of receive and transmit FIFO
that can be controlled through I2C or high-speed SPI."

SERIAL_SC16IS7XX
Supported ICs are SC16IS740, SC16IS741, SC16IS750, SC16IS752, SC16IS760 and SC16IS762.

[SiliconWizard]

You can refer to that: https://www.raspberrypi.org/documentation/configuration/uart.md
I think the RPi4 has the same limitation.

As said in the link, you can either disable BT if you don't use it, or switch BT to the mini-uart instead.

[luiHS]

 

Thanks to everyone for your replies.
I've tried both options, Mini UART and PL011, and both seem to work fine. I will probably use the PL011, because at this moment I don't need Bluetooth, I can use WIFI for wireless applications.