3.5.3.4. PRU-ICSS Serial UART¶

Introduction

As of Processor SDK v7.1, Linux supports the PRU UART peripheral within the PRU-ICSS, which is based on the industry standard TL16C550. The kenrel driver is at drivers/tty/serial/8250/8250_pruss.c.

Support Devices

AM335x devices

Supported Driver Features

Baud rates up to 12Mbps
Hardware flow control

Unsupported Driver Features

DMA support

Kernel Config

The PRUSS UART Linux kernel driver depends on the PRU-ICSS kernel drivers. So the following kernel Kconfig options should be enabled to use the PRUSS UART module.

Device Drivers  --->
      SOC (System On Chip) specific Drivers  --->
              [*] TI SOC drivers support  --->
                      <M>   TI PRU-ICSS Subsystem Platform drivers

Device Drivers  --->
      IRQ chip support  --->
              <M>   TI PRU-ICSS Interrupt Controller

Device Drivers  --->
      Character devices  --->
              Serial drivers  --->
                      <M> TI PRU-ICSS UART support

Example DT configuration

From am335x-evmsk.dts

&pruss_uart {
        prus = <&pru0>;
        ti,pru-interrupt-map = <0 6 2 2>;
        pinctrl-names = "default";
        pinctrl-0 = <&prussuart_pins>;
        status = "okay";
};

Driver Usage

Once the driver is probed, kernel log shows the following message.

[   28.617700] 4a328000.serial: ttyS1 at MMIO 0x4a328000 (irq = 77, base_baud = 12000000) is a 16550A

Therefore the device node /dev/ttyS1 is associated to the PRUSS UART, user space application can read/write this serial port. For detalls please refer to kenrel uart driver usage.

Note

The index in ttyS1 could vary depending on the serial alias configuration in the device tree.