Linux System Start - WAGO 750 Series Manual

50 •
Linux Fieldbus Coupler 750-860

Linux System Start

3.9 Linux System Start
The initialization follows after switching on the supply voltage, or after a
hardware reset. The Linux fieldbus coupler determines the I/O module
configuration and creates a process image.
First, the firmware loader (FWL) is started via the WAGO bootstrap loader
(BSL) which in turn will start the boot loader (U-Boot) for Linux. The BSL
cannot be deleted. The FWL may only be exchanged by WAGO after prior
consultation.
The boot loader (U-Boot) for Linux is under GPL and is therefore also in the
source code on the WAGO Linux distribution and can be changed or replaced.
This is only necessary if you intend to change the boot behavior of the Linux
kernel. To abort the boot loader boot process and to change to the U-Boot
environment you have to enter the password geheim (on the serial console)
when the following is output:
I2C-EEPROM detected.
I2C-RTC detected.
In: serial
Out: serial
Err: serial
Booting in 3 seconds - enter abort password to prevent this
The boot loader switches to its shell environment. If, after three seconds, no
password has been entered, the boot loader (U-Boot) loads the Linux kernel
from the flash memory, unpacks it into the RAM starting at address
0x0040000 and then starts it with the specified boot parameters. The kernel
startup scripts will then perform the following actions:
• Set timer IRQ
• Initialize RAM memory
• Embed the JFFS2 file system
• Start serial driver
• Embed LED driver
• Create partitions in the flash memory
• Load I2C driver: embed real-time clock chip/embed EEPROM
WAGO-I/O-SYSTEM 750
Linux Fieldbus Coupler