Hello Peter,

Did not understand... I must admit! As of my best interpretation SeaBIOS has 5 functions which makes BIOS legacy:

get and set variables, get and set real time clock, reset.

Or maybe, something changed.

I went back, to inspect CSM code in SeaBIOS, and found the following:

# General Features

# CONFIG_COREBOOT is not set

# CONFIG_QEMU is not set

CONFIG_CSM=y <<==================== set CSM ON

# CONFIG_QEMU_HARDWARE is not set

CONFIG_THREADS=y

CONFIG_RELOCATE_INIT=y

CONFIG_BOOTMENU=y

CONFIG_BOOTSPLASH=y

CONFIG_BOOTORDER=y

CONFIG_ENTRY_EXTRASTACK=y

CONFIG_MALLOC_UPPERMEMORY=y

CONFIG_ROM_SIZE=0

Then make:

Compile checking out/src/hw/pcidevice.o

Compile checking out/src/hw/ahci.o

Compile checking out/src/hw/pvscsi.o

Compile checking out/src/hw/usb-xhci.o

Compile checking out/src/hw/usb-hub.o

Compile checking out/src/hw/sdcard.o

Compile checking out/src/fw/coreboot.o

Compile checking out/src/fw/lzmadecode.o

Compile checking out/src/fw/multiboot.o

Compile checking out/src/fw/csm.o

Compile checking out/src/fw/biostables.o

Compile checking out/src/fw/paravirt.o

Compile checking out/src/fw/shadow.o

Compile checking out/src/fw/pciinit.o

Compile checking out/src/fw/smm.o

Compile checking out/src/fw/smp.o

Compile checking out/src/fw/mtrr.o

Compile checking out/src/fw/xen.o

Compile checking out/src/fw/acpi.o

Compile checking out/src/fw/mptable.o

Compile checking out/src/fw/pirtable.o

Compile checking out/src/fw/smbios.o

Where I see e820 table which is to be passed to OS, in order OS to understand what memory it can use. But I did not find explicitly these 5 functions. So I need a little help here. Where are these functions?

Now... How GRUB2 replaces all of these functionalities? I see what you said here (that GRUB2 is directly implemented into FW, thus skipping MBR), but who/what entity is replacing missing SeaBIOS functionalities?

Thank you,

Zoran