How to use UART for Diagnostic - Revision history

Wei.zeng at 09:29, 20 March 2020

2020-03-20T09:29:08Z

Wei.zeng at 09:25, 20 March 2020

2020-03-20T09:25:57Z

Wei.zeng: Created page with "Linux serial port/UART access from userspace is provided through tty-devices under /dev. Depending on the driver used to drive the UART, those devices can have different names..."

2020-03-20T09:24:06Z

Created page with "Linux serial port/UART access from userspace is provided through tty-devices under /dev. Depending on the driver used to drive the UART, those devices can have different names..."

New page

Linux serial port/UART access from userspace is provided through tty-devices under /dev. Depending on the driver used to drive the UART, those devices can have different names.

----

== [https://developer.toradex.cn/knowledge-base/uart-(linux)#Configuration Configuration] ==

From user space, one can use the command line utility stty to configure the serial speed. Then the port can be treated as as a regular file:
<pre style="background: rgb(255, 255, 255); margin: 3px 0px; padding: 10px; border-radius: 4px; border: 1px dotted rgb(204, 204, 204); color: rgb(0, 0, 0); text-transform: none; line-height: 1.4285; text-indent: 0px; letter-spacing: normal; overflow: auto; font-family: monospace !important; font-size: 14px; font-style: normal; font-weight: 400; word-spacing: 0px; display: block; white-space: pre-wrap; word-break: break-all; word-wrap: break-word; box-sizing: border-box; orphans: 2; widows: 2; tab-size: 4; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial; hyphens: none;"># stty -F /dev/ttyS1 115200
# echo Test > /dev/S1</pre>

Using C, use the struct termios to set the initial baud rate:
<pre style="background: rgb(255, 255, 255); margin: 3px 0px; padding: 10px; border-radius: 4px; border: 1px dotted rgb(204, 204, 204); color: rgb(0, 0, 0); text-transform: none; line-height: 1.4285; text-indent: 0px; letter-spacing: normal; overflow: auto; font-family: monospace; font-size: 14px; font-style: normal; font-weight: 400; word-spacing: 0px; display: block; white-space: pre-wrap; word-break: break-all; word-wrap: break-word; box-sizing: border-box; orphans: 2; widows: 2; tab-size: 4; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial; hyphens: none;" class="cpp">#include <termios.h>
...
struct termios tty;
int fd;
int flags = O_RDWR | O_NOCTTY | O_NONBLOCK;
 
fd = open("/dev/ttyS0", flags);
 
tcgetattr(fd, &tty);
 
tty.c_cflag = (tty.c_cflag & ~CSIZE) | CS8;
tty.c_cflag |= B115200;
 
if (tcsetattr (fd, TCSANOW, &tty) != 0)
{
fprintf (stderr, "error %d from tcsetattr", errno);
return -1;
}
</pre>

A fixed list of baud rates are pre-defined:
<div style="width: auto; color: rgb(0, 0, 0); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: arial, helvetica, sans-serif; font-size: 14px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; overflow-x: auto; min-height: 0.01%; box-sizing: border-box; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;" class="table-responsive">
{| style="margin: 4px 0px 6px; width: inherit !important; border-collapse: collapse; max-width: 99.9%; box-sizing: border-box; border-spacing: 0px; background-color: transparent;" class="table"
|- style="border-bottom-color: rgb(221, 221, 221); border-bottom-width: 1px; border-bottom-style: solid; box-sizing: border-box;"
! style="padding: 8px; width: inherit !important; text-align: left; color: rgb(255, 255, 255); line-height: 1.4285; font-weight: bold; vertical-align: middle; border-top-color: currentcolor; border-bottom-color: currentcolor; border-left-color: rgb(221, 221, 221); border-top-width: 0px; border-bottom-width: medium; border-left-width: 1px; border-top-style: none; border-bottom-style: none; border-left-style: solid; box-sizing: border-box; background-color: rgb(177, 177, 177) !important;" | Baud rate
! style="padding: 8px; width: inherit !important; text-align: left; color: rgb(255, 255, 255); line-height: 1.4285; font-weight: bold; vertical-align: middle; border-top-color: currentcolor; border-bottom-color: currentcolor; border-left-color: rgb(221, 221, 221); border-top-width: 0px; border-bottom-width: medium; border-left-width: 1px; border-top-style: none; border-bottom-style: none; border-left-style: solid; box-sizing: border-box; background-color: rgb(177, 177, 177) !important;" | Symbol
|- style="border-bottom-color: rgb(221, 221, 221); border-bottom-width: 1px; border-bottom-style: solid; box-sizing: border-box;"
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | 921600
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | B921600
|- style="box-sizing: border-box;"
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | 460800
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | B460800
|- style="border-bottom-color: rgb(221, 221, 221); border-bottom-width: 1px; border-bottom-style: solid; box-sizing: border-box;"
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | 230400
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | B230400
|- style="box-sizing: border-box;"
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | 115200
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | B115200
|- style="border-bottom-color: rgb(221, 221, 221); border-bottom-width: 1px; border-bottom-style: solid; box-sizing: border-box;"
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | 57600
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | B57600
|- style="box-sizing: border-box;"
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | 38400
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | B38400
|- style="border-bottom-color: rgb(221, 221, 221); border-bottom-width: 1px; border-bottom-style: solid; box-sizing: border-box;"
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | 19200
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | B19200
|- style="box-sizing: border-box;"
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | 9600
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | B9600
|- style="border-bottom-color: rgb(221, 221, 221); border-bottom-width: 1px; border-bottom-style: solid; box-sizing: border-box;"
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | 4800
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | B4800
|- style="box-sizing: border-box;"
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | 2400
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | B2400
|- style="border-bottom-color: rgb(221, 221, 221); border-bottom-width: 1px; border-bottom-style: solid; box-sizing: border-box;"
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | 1200
| style="padding: 8px; border: 1px solid rgb(221, 221, 221); width: inherit !important; line-height: 1.4285; vertical-align: top; box-sizing: border-box;" | B1200
|}
</div>
=== [https://developer.toradex.cn/knowledge-base/uart-(linux)#Nonstandard_baud_rate Non-standard baud rate] ===

==== [https://developer.toradex.cn/knowledge-base/uart-(linux)#vybrid-modules Vybrid modules] ====

With the following userspace C program one can configure UART custom baud rates:

<pre style="background: rgb(255, 255, 255); margin: 3px 0px; padding: 10px; border-radius: 4px; border: 1px dotted rgb(204, 204, 204); color: rgb(0, 0, 0); text-transform: none; line-height: 1.4285; text-indent: 0px; letter-spacing: normal; overflow: auto; font-family: monospace; font-size: 14px; font-style: normal; font-weight: 400; word-spacing: 0px; display: block; white-space: pre-wrap; word-break: break-all; word-wrap: break-word; box-sizing: border-box; orphans: 2; widows: 2; tab-size: 4; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial; hyphens: none;" class="cpp">#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <asm/termios.h>
 
int main(int argc, char* argv[]) {
 
int retval, fd, speed;
struct termios2 ntio;
 
if (argc != 3) {
printf("Usage: %s /dev/ttyXXX 20000\n", argv[0], argv[0]);
return -1;
}
 
speed = atoi(argv[2]);
fd = open(argv[1], O_RDONLY);
if (fd < 0) {
perror("Open");
return -1;
}
 
ioctl(fd, TCGETS2, &ntio);
ntio.c_cflag &= ~CBAUD;
ntio.c_cflag |= BOTHER;
ntio.c_ispeed = speed;
ntio.c_ospeed = speed;
retval = ioctl(fd, TCSETS2, &ntio);
close(fd);
 
if (retval == 0)
printf("New baud configured\n");
else
perror("ioctl");
 
return 0;
}
</pre>

[https://developer.toradex.cn/knowledge-base/uart-(linux)#RS485 RS-485]

The Carrier Board implements RS-485 using a single transceiver in a half-duplex communication mode, which means that one medium is shared for transmitting and receiving data. The transceiver switches to transmit mode when the RTS signal is asserted (low active).

RS-485 defines the electrical characteristics of drivers and receivers for serial communication and supports bus topology. How RS-485 is exactly implemented depends on application and requirements. The RS-485 support has been tested using the configuration as found on Carrier Boards.

[https://developer.toradex.cn/knowledge-base/uart-(linux)#user-space User Space]

On carrier boards the following flags should be used:
<pre style="background: rgb(255, 255, 255); margin: 3px 0px; padding: 10px; border-radius: 4px; border: 1px dotted rgb(204, 204, 204); color: rgb(0, 0, 0); text-transform: none; line-height: 1.4285; text-indent: 0px; letter-spacing: normal; overflow: auto; font-family: monospace !important; font-size: 14px; font-style: normal; font-weight: 400; word-spacing: 0px; display: block; white-space: pre-wrap; word-break: break-all; word-wrap: break-word; box-sizing: border-box; orphans: 2; widows: 2; tab-size: 4; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial; hyphens: none;"><code style="padding: 0px; border-radius: 0px; color: inherit; font-family: monospace !important; font-size: 14px !important; white-space: pre-wrap !important; box-sizing: border-box; background-color: transparent; overflow-wrap: break-word;">...
/* Enable RS485 mode: */
rs485conf.flags |= SER_RS485_ENABLED;

/* or, set logical level for RTS pin equal to 0 when sending: */
rs485conf.flags &= ~(SER_RS485_RTS_ON_SEND);

/* Set logical level for RTS pin equal to 1 after sending: */
rs485conf.flags |= SER_RS485_RTS_AFTER_SEND;

/* Enable receiver during sending, required for i.MX devices */
rs485conf.flags |= SER_RS485_RX_DURING_TX;
...
</code></pre>

[https://developer.toradex.cn/knowledge-base/uart-(linux)#enablingdisabling-dma Enabling/disabling DMA]

The current driver has a weak DMA implementation, which can lead to lock ups, especially on the RX side. The non-DMA (PIO) mode is much more robust, and thanks to the hardware FIFO also quite efficient. The easiest way to disable the DMA mode is to overwrite the dma-names property:
<pre style="background: rgb(255, 255, 255); margin: 3px 0px; padding: 10px; border-radius: 4px; border: 1px dotted rgb(204, 204, 204); color: rgb(0, 0, 0); text-transform: none; line-height: 1.4285; text-indent: 0px; letter-spacing: normal; overflow: auto; font-family: monospace !important; font-size: 14px; font-style: normal; font-weight: 400; word-spacing: 0px; display: block; white-space: pre-wrap; word-break: break-all; word-wrap: break-word; box-sizing: border-box; orphans: 2; widows: 2; tab-size: 4; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial; hyphens: none;">@@ -254,6 +254,7 @@

&uart0 {
status = "okay";
+ dma-names = "", "";
};

&uart1 {
</pre>

@@ Line 25: / Line 25: @@
 <span style="color: rgb(0, 0, 255); box-sizing: border-box;">if</span> <span style="color: rgb(0, 128, 0); box-sizing: border-box;">(</span>tcsetattr <span style="color: rgb(0, 128, 0); box-sizing: border-box;">(</span>fd, TCSANOW, <span style="color: rgb(0, 0, 64); box-sizing: border-box;">&</span>tty<span style="color: rgb(0, 128, 0); box-sizing: border-box;">)</span> <span style="color: rgb(0, 0, 64); box-sizing: border-box;">!</span><span style="color: rgb(0, 0, 128); box-sizing: border-box;">=</span> <span style="color: rgb(0, 0, 221); box-sizing: border-box;">0</span><span style="color: rgb(0, 128, 0); box-sizing: border-box;">)</span>
 <span style="color: rgb(0, 128, 0); box-sizing: border-box;">{</span>
-     <span style="color: rgb(0, 0, 221); box-sizing: border-box;">fprintf</span> <span style="color: rgb(0, 128, 0); box-sizing: border-box;">(</span><span style="color: rgb(0, 0, 255); box-sizing: border-box;">stderr</span>, <span style="color: rgb(255, 0, 0); box-sizing: border-box;">"error&nbsp;%d from tcsetattr"</span>, <span style="color: rgb(0, 0, 255); box-sizing: border-box;">errno</span><span style="color: rgb(0, 128, 0); box-sizing: border-box;">)</span><span style="color: rgb(0, 128, 128); box-sizing: border-box;">;</span>
+     <span style="color: rgb(0, 0, 221); box-sizing: border-box;">fprintf</span> <span style="color: rgb(0, 128, 0); box-sizing: border-box;">(</span><span style="color: rgb(0, 0, 255); box-sizing: border-box;">stderr</span>, <span style="color: rgb(255, 0, 0); box-sizing: border-box;">"error %d from tcsetattr"</span>, <span style="color: rgb(0, 0, 255); box-sizing: border-box;">errno</span><span style="color: rgb(0, 128, 0); box-sizing: border-box;">)</span><span style="color: rgb(0, 128, 128); box-sizing: border-box;">;</span>
      <span style="color: rgb(0, 0, 255); box-sizing: border-box;">return</span> <span style="color: rgb(0, 0, 64); box-sizing: border-box;">-</span><span style="color: rgb(0, 0, 221); box-sizing: border-box;">1</span><span style="color: rgb(0, 128, 128); box-sizing: border-box;">;</span>
-<span style="color: rgb(0, 128, 0); box-sizing: border-box;">}</span>
+<span style="color: rgb(0, 128, 0); box-sizing: border-box;">}</span></pre>
@@ Line 91: / Line 90: @@
 &nbsp;
 	<span style="color: rgb(0, 0, 255); box-sizing: border-box;">if</span> <span style="color: rgb(0, 128, 0); box-sizing: border-box;">(</span>argc <span style="color: rgb(0, 0, 64); box-sizing: border-box;">!</span><span style="color: rgb(0, 0, 128); box-sizing: border-box;">=</span> <span style="color: rgb(0, 0, 221); box-sizing: border-box;">3</span><span style="color: rgb(0, 128, 0); box-sizing: border-box;">)</span> <span style="color: rgb(0, 128, 0); box-sizing: border-box;">{</span>
-		<span style="color: rgb(0, 0, 221); box-sizing: border-box;">printf</span><span style="color: rgb(0, 128, 0); box-sizing: border-box;">(</span><span style="color: rgb(255, 0, 0); box-sizing: border-box;">"Usage:&nbsp;%s /dev/ttyXXX 20000<span style="color: rgb(0, 0, 153); font-weight: bold; box-sizing: border-box;">\n</span>"</span>, argv<span style="color: rgb(0, 128, 0); box-sizing: border-box;">[</span><span style="color: rgb(0, 0, 221); box-sizing: border-box;">0</span><span style="color: rgb(0, 128, 0); box-sizing: border-box;">]</span>, argv<span style="color: rgb(0, 128, 0); box-sizing: border-box;">[</span><span style="color: rgb(0, 0, 221); box-sizing: border-box;">0</span><span style="color: rgb(0, 128, 0); box-sizing: border-box;">]</span><span style="color: rgb(0, 128, 0); box-sizing: border-box;">)</span><span style="color: rgb(0, 128, 128); box-sizing: border-box;">;</span>
+		<span style="color: rgb(0, 0, 221); box-sizing: border-box;">printf</span><span style="color: rgb(0, 128, 0); box-sizing: border-box;">(</span><span style="color: rgb(255, 0, 0); box-sizing: border-box;">"Usage: %s /dev/ttyXXX 20000<span style="color: rgb(0, 0, 153); font-weight: bold; box-sizing: border-box;">\n</span>"</span>, argv<span style="color: rgb(0, 128, 0); box-sizing: border-box;">[</span><span style="color: rgb(0, 0, 221); box-sizing: border-box;">0</span><span style="color: rgb(0, 128, 0); box-sizing: border-box;">]</span>, argv<span style="color: rgb(0, 128, 0); box-sizing: border-box;">[</span><span style="color: rgb(0, 0, 221); box-sizing: border-box;">0</span><span style="color: rgb(0, 128, 0); box-sizing: border-box;">]</span><span style="color: rgb(0, 128, 0); box-sizing: border-box;">)</span><span style="color: rgb(0, 128, 128); box-sizing: border-box;">;</span>
 		<span style="color: rgb(0, 0, 255); box-sizing: border-box;">return</span> <span style="color: rgb(0, 0, 64); box-sizing: border-box;">-</span><span style="color: rgb(0, 0, 221); box-sizing: border-box;">1</span><span style="color: rgb(0, 128, 128); box-sizing: border-box;">;</span>
 	<span style="color: rgb(0, 128, 0); box-sizing: border-box;">}</span>
@@ Line 116: / Line 115: @@
 &nbsp;
 	<span style="color: rgb(0, 0, 255); box-sizing: border-box;">return</span> <span style="color: rgb(0, 0, 221); box-sizing: border-box;">0</span><span style="color: rgb(0, 128, 128); box-sizing: border-box;">;</span>
-<span style="color: rgb(0, 128, 0); box-sizing: border-box;">}</span>
+<span style="color: rgb(0, 128, 0); box-sizing: border-box;">}</span></pre>
 [https://developer.toradex.cn/knowledge-base/uart-(linux)#RS485 RS-485]
@@ Line 140: / Line 138: @@
      /* Enable receiver during sending, required for i.MX devices */
      rs485conf.flags |= SER_RS485_RX_DURING_TX;
-...
+...</code></pre>
 [https://developer.toradex.cn/knowledge-base/uart-(linux)#enablingdisabling-dma Enabling/disabling DMA]