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usage of Uart1 and Uart2 #437

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eroom1966 opened this Issue Jun 12, 2017 · 15 comments

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@eroom1966

eroom1966 commented Jun 12, 2017

Hi

I have been struggling to get the 2 UART interfaces working reliably, and have now seen a strange issue which seems to be related to my core issue

I have an external GPS receiver running at 9600 baud configured as follows
HardwareSerial SerGPS(1);
...
SerGPS(9600, SERIAL_8N1, 33, 32);

All works well, I stream the data from the GPS device and no issues, I can read and parse the messages

If I reconfigure to use UART2 (everything else remains the same), thus
HardwareSerial SerGPS(2);
...
SerGPS(9600, SERIAL_8N1, 33, 32);

Now using UART2 it becomes very unstable - the checksums on the messages fail and does not work reliably, this is very confusing from a S/W perspective, nothing has changed, only the internal configuration of the IO to UART mapping.

I will try to reduce to a simple testcase and share on this forum, but I am wondering has anybody else experienced a similar issue when trying to use UART2

Kind Regards
E

@claudeheintz

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claudeheintz commented Jun 12, 2017

I think that you need to change the pins to the ones muxed to UART2. I'm not clear if these are physical pin numbers or GPIO numbers. UART2 is mapped to GPIO 16 and 17 which are chip pins 25 and 27 respectively.

@copercini

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copercini commented Jun 12, 2017

Quite strange, For me it works fine:

HardwareSerial SerialGPS(2);
...
SerialGPS.begin(9600,SERIAL_8N1,33,32); //works

@eroom1966

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eroom1966 commented Jun 12, 2017

@claudeheintz
Hi Claude,
That is usefule information,
Can you provide a link to the reference that UART2 is muxed to GPIO 16 & 17 ?
Regards
E

update: OK, I see it here
https://www.espressif.com/sites/default/files/documentation/esp32_datasheet_en.pdf

@eroom1966 eroom1966 closed this Jun 12, 2017

@eroom1966

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eroom1966 commented Jun 12, 2017

@copercini
When you say

it works fine
Can you tell me what you mean ?

I am guessing that individual characters are incorrect due to the fact the calculated and provided checksums are differing.

Regards
E

@eroom1966 eroom1966 reopened this Jun 12, 2017

@copercini

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copercini commented Jun 12, 2017

@eroom1966
I just did some superficial tests with a SIM808, using AT commands

Using Serial2 or Serial1 with pins 33 and 32 the ESP32 send about 50 AT commands and SIM808 receive and respond it without any problems.

Did you tried with .begin in SerialGPS.begin(9600,SERIAL_8N1,33,32); ?

@eroom1966

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eroom1966 commented Jun 12, 2017

@claudeheintz
Follow up
https://www.espressif.com/sites/default/files/documentation/esp_wroom_32_datasheet_en.pdf
This document indicates that UART0 & UART1 can be muxed to any GPIO pins

@eroom1966

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eroom1966 commented Jun 12, 2017

@copercini

Did you tried with .begin in SerialGPS.begin(9600,SERIAL_8N1,33,32); ?

my posting was a typo, this is in fact what I have
sorry for the confusion
E

@claudeheintz

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claudeheintz commented Jun 12, 2017

In the technical reference manual it refers to the ability to connect pins in two ways. I'm not sure I completely understand. But, there is through the GPIO mux and through the I/O mux. With the latter, only specific signals can be assigned to a pin. The technical reference manual (https://espressif.com/en/support/download/documents?keys=&field_type_tid%5B%5D=13) indicates that using the I/O mux has better performance for high frequency signals (whatever that means).

I'm suggesting that if there is a corruption issue, even at 9600 baud, that using the pins specifically designated for U2TX and U2RX (rather than using the GPIO mux to assign any random pins) may make a difference.

@eroom1966

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eroom1966 commented Jun 12, 2017

@claudeheintz

I'm suggesting that if there is a corruption issue, even at 9600 baud, that using the pins specifically designated for U2TX and U2RX (rather than using the GPIO mux to assign any random pins) may make a difference.

This is definitely worth investigating, thanks for the pointer
Regards
E

@eroom1966 eroom1966 closed this Jun 12, 2017

@llewellynnu

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llewellynnu commented Aug 25, 2017

@eroom1966 Did using the Pins designated for UART2 Solve the issue you were facing?
I am asking since I am facing the exact same issue.

Regards

@eroom1966

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eroom1966 commented Aug 29, 2017

@llewellynnu
Yes I used the designated pins
Regards
E

@llewellynnu

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llewellynnu commented Aug 29, 2017

@eroom1966 Thanks a lot.
The only issue with using the designated pins is that ESP32-WROVER module GPIO 16 and 17 are not to be connected as its connected to PSRAM.

@claudeheintz

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claudeheintz commented Aug 30, 2017

Here is a useful article about re-assigning the pins for the serial ports on ESP32 boards:
http://hackaday.com/2017/08/17/secret-serial-port-for-arduinoesp32/

@Vorms

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Vorms commented Jan 5, 2018

I use the UART 2 on pin 16 and 17 and it is working well.
When I setup the UART1 with
HardwareSerial MP3Player
MP3Player.begin(9600, SERIAL_8N1, MP3PLAYER_RX, MP3PLAYER_TX);

The UART2 will be miss fonctioning.

Best regards

Thierry Vorms
vormsty@gmail.com

@Vorms

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Vorms commented Feb 28, 2018

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