Update README files

configs/sama5d4-ek/README.txt

@@ -855,6 +855,26 @@ Running NuttX from SDRAM
     2014-3-30:  These instructions were adapted from the Linux4SAM website
                 but have not yet been used.
 
+  Using JTAG
+  ----------
+
+  This description assumes that you have a JTAG debugger such as Segger
+  J-Link connected to the SAMA5D3-Xplained.
+
+  1. Start the GDB server
+  2. Start GDB
+  3. Use the 'target remote localhost:xxxx' command to attach to the GDG
+     server
+  4. Do 'mon reset' then 'mon go' to start the internal boot loader (maybe
+     U-Boot).
+  5. Let the boot loader run until it completes SDRAM initialization, then
+     do 'mon halt'.
+  6. Now you have SDRAM initialized and you use 'load nuttx' to load the
+     ELF file into SDRAM.
+  7. Use 'file nuttx' to load symbols
+  8. Set the PC to the NuttX entry point 'mon pc 0x20008040' and start
+     nuttx using 'mon go'.
+
 SAMA4D44-MB RevC PIO Usage
 ==========================