Booting the TS-7300 boards VHDL and C

Overview After looking at the general approach to booting machines (generally PCs) we will now look at the TS-7300 board Firstly some general observations on booting embedded boards –They quite often don’t have hard drives –They are frequently low power Need to drop into background – low power mode –They use un-attended boot mode. –They will use specialised/stripped down kernels.

TS board gotchas The TS-7300 differs from more commonly found boards in a number of ways –It doesn’t have on-board flash, so there is no real BIOS/BSP to speak of –It boots of an SD (Secure Digital) disc, so it use proprietory code

TS-7300 boot sequence On power on the ARM EP9302 CPU search for an on board boot device It can find them in a number of places –FLASH memory –UART (ay 9600 baud!)‏ –SPI interface It looks for a boot image to run either the OS or a BIOS/BSP

TS-7300 boot sequence On the TS-7300 board the SPI interface is used to talk with a 2k serial EEPROM The EEPROM has the string “CRUS” meaning that this is a bit of boot code The TS board downloads the 2k of code in the EEPROM into on-chip SRAM and executes it.

TS-7300 boot sequence The EEPROM code does some self testing, sets up SDRAM, bus timing, and Ethernet MAC addresses There is an (unused on our system) 36 byte security block at the end of the EEPROM that allows many security options. –Passwording –Locking to a specific sdcard

TS-7300 boot sequence The TS board now loads the boot sector from the SDCard into SDRAM 0x1000 This code, Thumb mode, is executed and allows access to further SDCard sectors and it loads in the compressed kernel and initrd into memory (the 1 st 2 disc partitions)‏

TS-7300 boot sequence ARM CPU EEPROM CODE In SRAM EEPROM SPI 0x1000 SDcard Boot sector 0x Compressed kernel 0x Initrd image SDCard Boot Sector Partition 1 Partition 2 Partition 3 (rootfs)‏ SDRAM Memory

TS-7300 boot sequence The Compressed kernel code is executed – it decompresses itself and then loads the initrd The initrd loads in the FPGA image and the kernel drivers for the SDCard The kernel then mounts the 3 rd partition on the SDCard and ‘pivots’ root to it. /sbin/init is started. The system is now up!