Boot sequence (Lizard)

From DAVE Developer's Wiki
Jump to: navigation, search

AM3517/AM3505 processor provides several options for the boot sequence. This section will describe in more detail the default boot sequence. For more details about bootstrap pin configurations please refer to Bootstrap configuration (Lizard). The default LELK configuration has U-Boot and Linux kernel in NOR flash memory and Root File System in NAND flash memory. The following table shows the flash partitions used with the default configuration:

Name MTD partition Device Size
U-Boot 0 NOR Flash 256 KB
U-Boot environment #1 1 NOR Flash 128 KB
U-Boot environment #2 2 NOR Flash 128 KB
Linux Kernel 3 NOR Flash 5120 KB
X-Loader (optional) 6 NAND Flash 512 kB
Root File System 10 NAND Flash 1040896 kB

NOR Boot

NOR flash boot sequence is easier and faster than NAND boot, mainly because X-Loader is not needed. When AM35xx comes out from reset, Boot ROM is executed in this mode to perform some basic initialization. After that, the CPU jumps at the beginning of GPMC CS0, where NOR flash reside, and U-Boot is started.

NAND Boot

X-Loader is the 2nd stage loader loaded by AM35xx Boot ROM to start 3rd stage tool like U-Boot when the NAND memory is configured as the boot flash. The Boot ROM code is always executed when the AM35xx comes out from reset and, after the first initialization step, it loads the X-Loader from storage memories (or from peripherals, like for example the serial port). X-Loader then retrieves U-Boot from flash memory (or from peripherals), which is in charge of launching the operating system.