add description of board specific environment variables

diff --git a/README.KARO-TX53 b/README.KARO-TX53
index 92ad39a462177474cb5b45454c17e0b009b542ae..2150204d917d1e596a507b8dda68979463952fc2 100644 (file)
--- a/README.KARO-TX53
+++ b/README.KARO-TX53
@@ -1,5 +1,5 @@
-                             Building & Flashing U-Boot for TX53
-                             ===================================
+                                        U-Boot for TX53
+                                        ===============
 
 Building U-Boot
 ---------------
@@ -34,3 +34,32 @@ nand erase.part u-boot;nand write ${fileaddr} u-boot ${filesize}
 
 If you want to revive a bricked module, you can use one of the
 flashtools provided with the BSP to reprogram the flash.
+
+
+U-Boot Features
+---------------
+
+Environment variables:
+
+cpu_clk       <CPU freq [MHz]>
+touchpanel    {tsc2007|edt-ft5x06}
+otg_mode      [host|device|none]
+video_mode    <video mode as understood by Linux fb_find_mode() function>
+              e.g.: VGA-1:640x480MR-24@60
+baseboard     {stk5-v3|stk5-v5} selects type of baseboard
+             'stk5-v5' setting enables CAN transceiver switch on GPIO4_21 and
+             disables USB Host mode on USBOTG port.
+             strings not starting in 'stk5' prevent the STK5 specific
+             pad initialization to be done.
+splashimage   memory address of a BMP file to be displayed instead of
+             the built-in logo. Since NAND flash is not accessible in
+             a memory mapped fashion, U-Boot will try to load the
+             contents of the flash partition 'logo' to the address
+             given with 'splashimage'.
+
+Note: Some variables (like 'cpu_clk' or 'splashimage') may render the
+      board unbootable if incorrectly set. Therefore these variables
+      will not be evaluated in case the board has been reset through a
+      watchdog reset or a character is available on the serial console
+      during startup to give the user a chance to recover from this
+      situation.