Aria technical documentation

Using the Serial ports on Aria G25 SOM

Using this device three I have enabled up to 3 USARTs and 2 UARTs

• acme-aria-serial.dts

To test it just save this file in the /boot directory of Aria G25 or in the first microSD partition. I have used this image (Kernel Linux 4.19.128 - Debian Buster 10) to try.

• acme-aria.dtb

To check the serial port enabled type this command:

acme@aria:~$ dmesg | grep serial
    [    0.359375] fffff200.serial: ttyS0 at MMIO 0xfffff200 (irq = 16, base_baud = 8333333) is a ATMEL_SERIAL
    [    0.679687] f801c000.serial: ttyS1 at MMIO 0xf801c000 (irq = 23, base_baud = 8333333) is a ATMEL_SERIAL
    [    0.687500] f8020000.serial: ttyS2 at MMIO 0xf8020000 (irq = 24, base_baud = 8333333) is a ATMEL_SERIAL
    [    0.695312] f8024000.serial: ttyS3 at MMIO 0xf8024000 (irq = 25, base_baud = 8333333) is a ATMEL_SERIAL
    [    0.710937] f8040000.serial: ttyS4 at MMIO 0xf8040000 (irq = 26, base_baud = 8333333) is a ATMEL_SERIAL
    [    0.718750] f8044000.serial: ttyS5 at MMIO 0xf8044000 (irq = 27, base_baud = 8333333) is a ATMEL_SERIAL

To see the devices activated type:

acme@aria:~$ ls -al /dev/ttyS*
    crw------- 1 acme tty     4, 64 Mar  4 19:07 /dev/ttyS0
    crw-rw---- 1 root dialout 4, 65 Mar  4 18:56 /dev/ttyS1
    crw-rw---- 1 root dialout 4, 66 Mar  4 18:56 /dev/ttyS2
    crw-rw---- 1 root dialout 4, 67 Mar  4 18:56 /dev/ttyS3
    crw-rw---- 1 root dialout 4, 68 Mar  4 18:56 /dev/ttyS4
    crw-rw---- 1 root dialout 4, 69 Mar  4 18:56 /dev/ttyS5

Pinout and device tree definitions port by port

USART0

usart0: serial@f801c000 {
    status = "okay";
};

USART1

usart1: serial@f8020000 {
    status = "okay";
};

USART2

usart2: serial@f8024000 {
    status = "okay";
}; 

USART3

usart3: serial@f8028000 {
    status = "okay";
};

UART0

uart0: serial@f8040000 {
    status = "okay";
};

UART1

uart1: serial@f8044000 {
    status = "okay";
};

DBGU Debug serial port (/dev/ttyS0)

The debug port is used just for the boot message

dbgu: serial@fffff200 {
    status = "okay";
};

User space programming

Python example

Install Python3 and Python Serial by typing:

sudo apt update
sudo apt install python3 python3-serial

Use this basic example or go to pySerial library web site:

import serial
import time

ser = serial.Serial(
    port='/dev/ttyS1',
    baudrate=460800,
    timeout=1,
    parity=serial.PARITY_NONE,
    stopbits=serial.STOPBITS_ONE,
    bytesize=serial.EIGHTBITS
)

for packet in range(100):
        for value in range(10):
                for i in range(50):
                        ser.write(chr(value+0x30).encode())
                ser.write(b'\r\n')
        ser.write(b'\r\n\n') 
        print(packet)
ser.flush()

time.sleep(1)
ser.close()

Read any bytes received on serial line and print out on stdout in hex format:

import sys
import serial
 
ser = serial.Serial(
    port='/dev/ttyUSB1', 
    baudrate=9600, 
    timeout=1,
    parity=serial.PARITY_NONE,
    stopbits=serial.STOPBITS_ONE,
    bytesize=serial.EIGHTBITS
)  

linecounter=0
bytecounter=0
bytesperline = 8
while True:     
    bytesToRead = ser.inWaiting()
    
    if bytesToRead>0:
        value=ser.read(1)
        if (bytecounter % bytesperline) == 0:
            print "\n[%04X] - " % bytecounter ,
            sys.stdout.flush()
            linecounter=linecounter+1
             
        print "%02X " % ord(value) ,
        sys.stdout.flush()
        bytecounter=bytecounter+1
        if bytecounter==0:
            print
            bytecounter=0

C example

This is a basic example on how to use a serial port in C.

Refer to these links to understand how it works.

• Termios
• GNU Low-level I/O doc

#include "stdio.h"     
#include "string.h"    
#include "unistd.h"    
#include "fcntl.h"     
#include "errno.h"     
#include "sys/types.h"
#include "sys/stat.h"
#include "stdlib.h"
#include "stdarg.h"
#include "termios.h"
 
int main(void) {
    char txBuffer[10];
    char rxBuffer[10];
    int fd;
    struct termios tty_attributes;
 
    if ((fd = open("/dev/ttyS1",O_RDWR|O_NOCTTY|O_NONBLOCK))<0) {
        fprintf (stderr,"Open error on %s\n", strerror(errno));
        exit(EXIT_FAILURE);
    } else {
        tcgetattr(fd,&tty_attributes);
 
        // c_cflag
        // Enable receiver
        tty_attributes.c_cflag |= CREAD;        
 
        // 8 data bit
        tty_attributes.c_cflag |= CS8;          
 
        // c_iflag
        // Ignore framing errors and parity errors. 
        tty_attributes.c_iflag |= IGNPAR;       
 
        // c_lflag
        // DISABLE canonical mode.
        // Disables the special characters EOF, EOL, EOL2, 
        // ERASE, KILL, LNEXT, REPRINT, STATUS, and WERASE, and buffers by lines.
 
        // DISABLE this: Echo input characters.
        tty_attributes.c_lflag &= ~(ICANON);     
 
        tty_attributes.c_lflag &= ~(ECHO);      
 
        // DISABLE this: If ICANON is also set, the ERASE character erases the preceding input  
        // character, and WERASE erases the preceding word.
        tty_attributes.c_lflag &= ~(ECHOE);     
 
        // DISABLE this: When any of the characters INTR, QUIT, SUSP, or DSUSP are received, generate the corresponding signal. 
        tty_attributes.c_lflag &= ~(ISIG);      
 
        // Minimum number of characters for non-canonical read.
        tty_attributes.c_cc[VMIN]=1;            
 
        // Timeout in deciseconds for non-canonical read.
        tty_attributes.c_cc[VTIME]=0;           
 
        // Set the baud rate
        cfsetospeed(&tty_attributes,B9600);     
        cfsetispeed(&tty_attributes,B9600);
 
        tcsetattr(fd, TCSANOW, &tty_attributes);
 
        txBuffer[0]='A';
        write(fd,txBuffer,1);
 
        // Read a char
        if (read(fd,&rxBuffer,1)==1) {
            printf("%c",rxBuffer[0]);
            printf("\n");
        }   
    }   
 
    close(fd);  
    return EXIT_SUCCESS;
}

Related links

• Atmel SAM9G25 Datasheet
• Atmel usart binding
• Aria G25 - Enable DMA on the serial ports to avoid rx overruns
• DMA bindings

Sergio Tanzilli
Systems designer, webmaster of www.acmesystems.it and founder of Acme Systems srl

Personal email: tanzilli@acmesystems.it
Web pages: https://www.acmesystems.it --- https://www.acmestudio.it
Github repositories: https://github.com/tanzilli --- https://github.com/acmesystems
Telegram group dedicated to the Acme Systems boards: https://t.me/acmesystemssrl

Aria technical documentation