Updated README files and comments

1 files changed, 24 insertions, 0 deletions

diff --git a/nuttx/configs/sama5d3-xplained/README.txt b/nuttx/configs/sama5d3-xplained/README.txt
index 2f6206dd3..eea1ae338 100644
--- a/nuttx/configs/sama5d3-xplained/README.txt
+++ b/nuttx/configs/sama5d3-xplained/README.txt
@@ -2625,6 +2625,30 @@ Configurations
      create a very corrupt configuration that may not be easy to recover
      from.
 
+  4. The SAMA5Dx is running at 396MHz by default in these configurations.
+     This is because the original timing for the PLLs, NOR FLASH, and SDRAM
+     came from the Atmel NoOS sample code which runs at that rate.
+
+     The SAMA5Dx is capable of running at 528MHz, however, and is easily
+     re-configured:
+
+       Board Selection -> CPU Frequency
+         CONFIG_SAMA5D3xEK_396MHZ=n     # Disable 396MHz operation
+         CONFIG_SAMA5D3xEK_528MHZ=y     # Enable 528MHz operation
+
+     If you switch to 528MHz, you should also check the loop calibration
+     value in your .config file.  Of course, it would be best to re-calibrate
+     the timing loop, but these values should get you in the ballpark:
+
+       CONFIG_BOARD_LOOPSPERMSEC=49341  # Calibrated on SAMA5D3-EK at 396MHz
+                                        # running from ISRAM
+       CONFIG_BOARD_LOOPSPERMSEC=65775  # Calibrated on SAMA4D3-Xplained at
+                                        # 528MHz running from SDRAM
+
+     Operation at 528MHz has been verified but is not the default in these
+     configurations because most testing was done at 396MHz.  NAND has not
+     been verified at these rates.
+
   Configuration Sub-directories
   -----------------------------
   Summary:  Some of the descriptions below are long and wordy. Here is the