-For DDR parameter tuning up and debugging, the interactive DDR debugging can
-be activated by saving an environment variable "ddr_interactive". The value
-doesn't matter. Once activated, U-boot prompts "FSL DDR>" before enabling DDR
-controller. The available commands can be seen by typing "help".
+For DDR parameter tuning up and debugging, the interactive DDR debugger can
+be activated by setting the environment variable "ddr_interactive" to any
+value. (The value of ddr_interactive may have a meaning in the future, but,
+for now, the presence of the variable will cause the debugger to run.) Once
+activated, U-boot will show the prompt "FSL DDR>" before enabling the DDR
+controller. The available commands are printed by typing "help".
+
+Another way to enter the interactive DDR debugger without setting the
+environment variable is to send the 'd' character early during the boot
+process. To save booting time, no additional delay is added, so the window
+to send the key press is very short -- basically, it is the time before the
+memory controller code starts to run. For example, when rebooting from
+within u-boot, the user must press 'd' IMMEDIATELY after hitting enter to
+initiate a 'reset' command. In case of power on/reset, the user can hold
+down the 'd' key while applying power or hitting the board's reset button.