u/Far_Permission5162

i made a custom bootloader for my rpi zero 2w using u-boot. copied the u-boot.bin with bootcode, start.elf, fixup.dat, a dtb file all from the repo of rpi/firmware.
i also made a short config,txt with the following
arm_64bit=1
enable_uart=1
kernel=u-boot.bin
core_freq=250

but when i insiert the sd card with the above contents with my laptop connected to uart port through usb-ttl i dont see the u-boot logs or console.
the activity led blinks 4 times . that is the pattern observed.