topic Re: imx6ull uart receive in i.MX Processors

imx6ull uart receive

Oman — Mon, 04 Jan 2021 11:03:12 GMT

In the imx6ull platform, the serial port encounters abnormal data reception. The description is as follows:

Problem Description:

If the external device is connected to the imx6ull serial port, it will emit a noise that low level when it sleeps,The waveform is a low level, about 40 ~ 50us.The baud rate of communication is 9600bps, 8n1

Read serial port data for a long time in imx6ull application layer, and receive data of 0xff all the time.

Q1. After calculating 9600 baud rate, the start bit time is 104us, while the time of 40 ~ 50us should not be recognized as the beginning of a data by the serial controller. Why can we receive the binary data of 0xff?

Q2. After testing, it is found that if the external device is disconnected, the application program can still read the secondary data of 0xff. Why can the data still be read after the device is disconnected?

this question happend at EVB board,I think it's the linux driver that causes this problem.

All IMX platform should all have it.

You can use GPIO port to simulate TX for testing

Re: imx6ull uart receive

jamesbone — Mon, 04 Jan 2021 20:53:43 GMT

Unfortunately if the external device connected to the i.Mx6ULL UART, it is taking Down the level of the signal for more than 40us that´s more than enough to validate in the UART mechanism that an Start bit it is available there is no option to remove this mechanism, or configure it.

I recommend if the external device can be attach through another component as glue logic, let´s said a buffer or any other device like a transistor to avoid this low level.

Have a happy new year

Re: imx6ull uart receive

Oman — Tue, 05 Jan 2021 02:28:25 GMT

Thinks for your reply.

I agree with you, but the key to the problem is to receive 0 XFF all the time.According to your analysis, the only time to receive 0xff is when 40us is received, but actually the received 0xff is like flood the screen, and it's useless to disconnect the external device.

Re: imx6ull uart receive

michaelyang — Tue, 05 Jan 2021 04:34:43 GMT

HI james， i meet this issue too, the discription as below:

connection type : RTU terminal <--->RS232<--->i.Mx6ULL

1. RTU output about 40us down level signal (the signal acturally is RTU sleep signal)

2. the i.Mx6ULL received this down level signal as the UART start bit, so the RS 232 will keep open status 3. while the next signal is normal data signal, it is normal, but after the normal data transfer end, that thte RTU will repeat send the sleep down level signal, the RS232 keep in open status. if this cycle repeat about 10 times ,that the i.Mx6ULL will keep output 0xff eventhough switch off the connection RS232 and i.Mx6ULL hope get your response earlier~

Re: imx6ull uart receive

BiyongSUN — Tue, 05 Jan 2021 05:42:13 GMT

Double confirm right config the tty, ex: is using stty to disable the echo.

stty -F /dev/ttymxc2 -echo

Re: imx6ull uart receive

Oman — Tue, 05 Jan 2021 06:22:38 GMT

Hi Biyong,

I have done test,and added your said.But the problem is still exist.

Showing settings:

#stty -F /dev/ttymxc3

speed 9600 baud; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>; eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V; flush = ^O; min = 1; time = 5;
ignbrk -brkint -icrnl -imaxbel
-opost -onlcr
-isig -icanon -iexten -echo -echoe -echok -echoctl -echoke

Should it have taken effected?

I added some log in kernel driver code.To print the value of registers.

[ 1341.230883] dma_rx_callback, count=4096 ## urxd:80ff 80:d0d, 84:4027, 88:704, 8c:4042, 90:b10, 94:2010, 98:408d, 9c:2b, a0:0, a4:29, a8:c34, ac:4, b0:2ca4, b4:40, b8:0,

80,84,88 ... is offset of register.And the after number is its value.

So we can not see uart controller have reported errors,but the count is 4096.

I disconnected RX line, it still print.

Re: imx6ull uart receive

BiyongSUN — Tue, 05 Jan 2021 07:13:50 GMT

How is loopback test?

Re: imx6ull uart receive

BiyongSUN — Tue, 05 Jan 2021 07:15:06 GMT

/unit_tests/UART/mxc_uart_stress_test.out

Usage:

./mxc_uart_stress_test.out <PORT> <BAUDRATE> <F> <R/W/L/D> <X> <Y> <O>

<PORT>: like /dev/ttymxc4

<BAUDRATE>: the baud rate number value (0~4000000)

<F>: enable flow control; other chars: disable flow control

<R/W/L/D>: R: read test; W: write test; L:loopback test; full duplex test

<X> : the group number: >= 1

<Y> : the group size: 1 - 1000

<O> : print log; other chars: disable log

Re: imx6ull uart receive

Oman — Tue, 05 Jan 2021 07:17:01 GMT

Execute command line at the other terminal:

minicom -w -H -D /dev/ttymxc3 -b 9600

Re: imx6ull uart receive

Oman — Tue, 05 Jan 2021 07:29:12 GMT

I try to test, follow result:

root@imx6ull14x14evk:~# /unit_tests/mxc_uart_test.out /dev/ttymxc3 9600 A L 10 10 O
Test: MXC UART!
Usage: mxc_uart_test <UART device name, opens UART2 if no dev name is specified>
/dev/ttymxc3 opened
Attributes set
Test: IOCTL Set
Data Written= Test
Data Read back= Test

I don't seem to know how to use it. I'll try.

Re: imx6ull uart receive

Oman — Thu, 07 Jan 2021 01:42:47 GMT

There are still problems in reading from the real Rx line.

I think the problem is linux drivers for uart or hardware of chip,not the app settings or other.

Re: imx6ull uart receive

Oman — Wed, 06 Jan 2021 09:35:22 GMT

Hi BiyongSun,

Because I don't know much about the working principle of thatprogram for mxc_uart_stress_test.out , can my above tests see where my main question is?

Re: imx6ull uart receive

BiyongSUN — Wed, 06 Jan 2021 10:38:38 GMT

The mxc_uart_stress_test.out is standard program coding follow the Linux standard. not a special program.

./mxc_uart_stress_test.out /dev/ttymxc2 115200

---- Running < ./mxc_uart_stress_test.out > test ----

Serial port /dev/ttymxc2 opened
NOT Using flow control
Speed set to 115200

write done : total : 200
write : 10 calls issued, 20 bytes per call
:)[ 1 ] READ is good., count : 20
:)[ 2 ] READ is good., count : 20
:)[ 3 ] READ is good., count : 20
:)[ 4 ] READ is good., count : 20
:)[ 5 ] READ is good., count : 20
:)[ 6 ] READ is good., count : 20
:)[ 7 ] READ is good., count : 20
:)[ 8 ] READ is good., count : 20
:)[ 9 ] READ is good., count : 20
:)[ 10 ] READ is good., count : 20

read done : total : 200
read : 10 calls issued, 20 bytes per call

---- Test < ./mxc_uart_stress_test.out > ended ----

Re: imx6ull uart receive

BiyongSUN — Wed, 06 Jan 2021 10:42:50 GMT

if you read the code of mxc_uart_stress_test.out(mxc_uart_stress_test.c), all the APIs, including header are only Linux layer. that is why I told you. It is not a special program. If you know about the Linux program, you can read the code. and understand the usage.

Re: imx6ull uart receive

BiyongSUN — Thu, 07 Jan 2021 01:21:56 GMT

sorry. forgot to give you the command line

/unit_tests/UART/mxc_uart_stress_test.out /dev/ttymxc2 115200 D L 10 20 O

Re: imx6ull uart receive

Oman — Thu, 07 Jan 2021 05:58:15 GMT

Dear @BiyongSUN :

Well,I tested. And the execute results are attached.

According to the results, the loopback test is good. but there are still problems in reading from the real Rx line.

Re: imx6ull uart receive

Oman — Fri, 08 Jan 2021 02:36:16 GMT

@BiyongSUN ,

How to verify next?

Do you have any suggestions?

Re: imx6ull uart receive

BiyongSUN — Fri, 08 Jan 2021 15:35:35 GMT

The internal loop already shows i.MX has no problem.

It probably has hardware connections issue.

you can ask your hardware engineer to help you rework and test the external loop back to double confirm the issue.

Re: imx6ull uart receive

Oman — Mon, 11 Jan 2021 01:35:11 GMT

Yes, the external terminal device sends a noise signal to 6ull, but it is recognized as valid data by 6ull, and always reports 0xff. My question is, can 6ull not be recognized as valid data?

Re: imx6ull uart receive

BiyongSUN — Mon, 11 Jan 2021 04:24:49 GMT

have you even set the Parity like stty parenb, parodd does, which will pass to the i.MX6ULL?