Enabling 2:nd USART on RS nodes


Revision
--------
0.3 2019-04-25

Background
----------
The AtMega128rfa1 and AtMegarf256r2 series shares uart1 pins with
interrupts pin p0 and p1. So we have to chose function. The default
function has been to use the interrups pins. In same applications the
usart1 would rather be preferred. Experimental and the mod is on your
own risk.

With some HW & SW modifications it is possible to enable usart1.
It needs skill for soldering/desoldering of SMD components.

Hardware modifications
 ----------------------
* Front side mods
Remove R301 (Pull-up for CON_INT5)

See pict:
---------
http://radio-sensors.com/pictures/usart1-mod-front.jpg


* Back side mods
Remove R776, R777, R778, R779 and U777 (This is the comparator unit)
Make a patch between R776 (right pad) to the 2-pin header CON_COMP

See pict:
---------
http://radio-sensors.com/pictures/usart1-mod-back.jpg


You now have usart1 on:
RX1 on P0  (white cable seen on front pict)
TX1 on P1  (grey cable seen on front pict)
           (black is GND seen on front pict)

Desoldering tips
----------------
https://www.google.com/search?client=ubuntu&channel=fs&q=desolering+SM+resistors&ie=utf-8&oe=utf-8#kpvalbx=1


Software modifications
----------------------
This will be a part of the platform code.

Now the support is via the commit below:
https://github.com/posjodin/contiki
in branch coap.

commit 57f3d5dbfe4070b3e9f602fa586329ccbb5b6b90
Author: Robert Olsson <robert@herjulf.se>
Date:   Sun Jan 27 22:13:22 2019 +0100

    Support for USART1 avr-rss2 platform
        modified:   platform/avr-rss2/contiki-conf.h
        modified:   platform/avr-rss2/contiki-main.c
        modified:   platform/avr-rss2/rss2.h

The essential code:
 -  rs232_init(RS232_PORT_0, RS232_BAUDRATE, USART_PARITY_NONE | USART_STOP_BITS_1 | USART_DATA_BITS_8);
-  rs232_redirect_stdout(RS232_PORT_0);
+  rs232_init(RS232_PORT_0, USART0_CONF_BAUD_RATE, USART_PARITY_NONE | USART_STOP_BITS_1 | USART_DATA_BITS_8);
 
+  /* UART1 Disables P0, P1 interrups pin and need HW fix for rss2 */
+#ifdef USART1_CONF_ENABLE
+  rs232_init(RS232_PORT_1, USART1_CONF_BAUD_RATE, USART_PARITY_NONE | USART_STOP_BITS_1 | USART_DATA_BITS_8);
+#endif 
+  
+  rs232_redirect_stdout(SERIAL_LINE_CONF_UART);




Configuration
-------------
User defines:
 USART1_CONF_ENABLE     to enable usart1
 USART1_CONF_BAUD_RATE  speed
 SERIAL_LINE_CONF_UART  control Contiki console output usart0 or usart1


Example from project_conf.h
.
.
#define USART1_CONF_ENABLE 1 
#define USART1_CONF_BAUD_RATE   USART_BAUD_38400
//#define SERIAL_LINE_CONF_UART 1