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 Can the second uart of carambola be used in openwrt 
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Joined: 24 Aug 2013, 20:35
Posts: 1
Hi,

I have a requirement where i need the carambola to connect and talk to another MCU using UART.

The carambola 2 (using ar9331 soc) seems to have only one UART which is used for serial console access and by the bootloader. The problem is i cannot send anything unwanted to the serial lines even during the bootup process and also once the openwrt starts. In short the UART has to be completely silent unless used by the application. Also seems like the software UART implementation using GPIO cannot achive higher baudrates (i am looking for baudrate > 115200). Is there a possible way to achieve this in AR9331 (completely disable the Serial UART) and for bootloader use the modified webgui enabled uboot. If this is possible how easy is it to acheive it.

Also I hope that i could use the second UART of carambola (using RT3050) in the openwrt. does the stock openwrt for carambola has the second UART enabled by default.


24 Aug 2013, 20:50
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Joined: 21 Aug 2013, 21:21
Posts: 81
sp923 wrote:
... has to be completely silent unless used by the application ...

Hi! My idea for carambola2 is to choose an additional 3rd pin that bootstraps in low mode, then connect it parallel with TX pin to a logical AND gate like 74HC08 > output of AND gate will be fully silent until You set the 3rd pin to high by software (and dont forget to remove serial console from port too) !


24 Aug 2013, 21:07
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Joined: 18 Nov 2013, 18:44
Posts: 39
Can you explain in a bit more detail how you succeded completely silencing serial console? This is awesome!


19 Apr 2014, 17:44
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Joined: 18 Nov 2013, 18:44
Posts: 39
sp923 wrote:
Also seems like the software UART implementation using GPIO cannot achive higher baudrates


Can you explain how to get anykind of uart via other gpio pins, I need anything, even a slow connection would work for me... thanks!


19 Apr 2014, 17:46
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Joined: 06 Dec 2012, 09:09
Posts: 24
Why not use a SPI or I2C UART chip like the one from Maxim?

http://www.maximintegrated.com/datasheet/index.mvp/id/6463


20 May 2014, 06:43
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Joined: 11 Mar 2012, 18:42
Posts: 18
valent wrote:
Can you explain in a bit more detail how you succeded completely silencing serial console? This is awesome!

1. You need to disable serial console in U-Boot (my modification has this option: https://github.com/pepe2k/u-boot_mod/bl ... kefile#L10).
2. Disable serial console in kernel (command line).


20 May 2014, 11:10
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Joined: 18 Nov 2013, 18:44
Posts: 39
I saw some sporadic mentions that some people got uart0 to work on Carambola 2, while leaving default uart1 for console.
Does anybody have more info how to enable uart0 on Carambola 2? Having two uarts on Carambola 2 would be awesome!


18 Aug 2014, 13:45
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Joined: 18 Nov 2013, 18:44
Posts: 39
Update: I see my mistake, people that are talking about using uart0 (second uart) are using Carambola 1 and I thought that they also have Carambola 2 as I do. Ufff, I really would like to have two uarts on Carambola 2.


18 Aug 2014, 14:11
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Joined: 11 Jun 2014, 14:45
Posts: 50
Not a true solution, but if you badly need a second UART on Carambola2, you can use USB to COM adapter.


18 Aug 2014, 14:30
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