+
+Voltage ID and VDD override
+--------------------
+T4240 has a VID feature. U-boot reads the VID efuses and adjust the voltage
+accordingly. The voltage can also be override by command vdd_override. The
+syntax is
+
+vdd_override <voltage in mV>, eg. 1050 is for 1.050v.
+
+Upon success, the actual voltage will be read back. The value is checked
+for safety and any invalid value will not adjust the voltage.
+
+Another way to override VDD is to use environmental variable, in case of using
+command is too late for some debugging. The syntax is
+
+setenv t4240qds_vdd_mv <voltage in mV>
+saveenv
+reset
+
+The override voltage takes effect when booting.
+
+Note: voltage adjustment needs to be done step by step. Changing voltage too
+rapidly may cause current surge. The voltage stepping is done by software.
+Users can set the final voltage directly.
+
+2-stage NAND/SD boot loader
+-------------------------------
+PBL initializes the internal SRAM and copy SPL(160K) in SRAM.
+SPL further initialise DDR using SPD and environment variables
+and copy u-boot(768 KB) from NAND/SD device to DDR.
+Finally SPL transers control to u-boot for futher booting.
+
+SPL has following features:
+ - Executes within 256K
+ - No relocation required
+
+Run time view of SPL framework
+-------------------------------------------------
+|Area | Address |
+-------------------------------------------------
+|SecureBoot header | 0xFFFC0000 (32KB) |
+-------------------------------------------------
+|GD, BD | 0xFFFC8000 (4KB) |
+-------------------------------------------------
+|ENV | 0xFFFC9000 (8KB) |
+-------------------------------------------------
+|HEAP | 0xFFFCB000 (50KB) |
+-------------------------------------------------
+|STACK | 0xFFFD8000 (22KB) |
+-------------------------------------------------
+|U-boot SPL | 0xFFFD8000 (160KB) |
+-------------------------------------------------
+
+NAND Flash memory Map on T4QDS
+--------------------------------------------------------------
+Start End Definition Size
+0x000000 0x0FFFFF u-boot img 1MB
+0x140000 0x15FFFF u-boot env 128KB
+0x160000 0x17FFFF FMAN Ucode 128KB
+
+Micro SD Card memory Map on T4QDS
+----------------------------------------------------
+Block #blocks Definition Size
+0x008 2048 u-boot img 1MB
+0x800 0016 u-boot env 8KB
+0x820 0128 FMAN ucode 64KB
+
+Switch Settings: (ON is 1, OFF is 0)
+===============
+NAND boot SW setting:
+SW1[1:8] = 10000010
+SW2[1.1] = 0
+SW6[1:4] = 1001
+
+SD boot SW setting:
+SW1[1:8] = 00100000
+SW2[1.1] = 0