Simple script that boots a kernel using tegrarcm by creating an image containing U-boot and the kernel concatenated.

tegrarcmboot.py

#!/bin/python3

# Simple script that boots a kernel using tegrarcm by creating an image
# containing U-boot and the kernel concatenated.
#
# Usage: boot.py board.bct zImage tegraxx-board.dtb
#
# The files listed below must be present in the working directory and
# can be obtained from U-boot.

uboot_img = "u-boot-nodtb-tegra.bin"
uboot_dtb = "u-boot.dtb"

import sys
import os

outfile = "u-boot-linux.img"

loadaddr = 0x80108000

# Adapt these to suit your need, e.g. for mounting a root FS on a SD card
kernel_args = 'cma=384M console=ttyS0,115200n8 console=tty1 rootwait rw'

bootcmd = 'setenv bootargs ' + kernel_args + ';'

bct = sys.argv[1]
zImage = sys.argv[2]
zImage_dtb = sys.argv[3]
if len(sys.argv) > 4:
    ramfs = sys.argv[4]
else:
    ramfs = None

class Padder:
    def __init__(self, out):
        self.out = out
        self.pos = 0

    def cat(self, f):
        fin = open(f, 'rb')
        content =  fin.read()
        self.pos += len(content)
        self.out.write(content)
        fin.close()
        
    def pad(self, to):
        if to < self.pos:
            raise Exception("output file position too high")

        pad = to - self.pos
        self.out.write((' ' * pad).encode('ascii'))
        self.pos = to
    
    def align(self, mask):
        to = (self.pos + (mask - 1)) & ~(mask - 1)
        self.pad(to)

outf = open(outfile, 'wb')

padder = Padder(outf)
padder.cat(uboot_img)
# Compute the future offset of the kernel and its DTB. We reserve 128KB for U-boot's DTB and heap. It may need to be increased further in the future.
#kernoffset = (padder.pos + 0x100000 + (0x10000 - 1)) & ~(0x10000 - 1)
#dtboffset = kernoffset + os.stat(zImage).st_size

# Above doesn't work anymore. Just set large enough addresses so the kernel won't screw itself while uncompressing.
kernoffset = 0x1000000
dtboffset = (kernoffset + os.stat(zImage).st_size + (0x10000 - 1)) & ~(0x10000 - 1)

if ramfs:
    ramfsoffset = (dtboffset + 0x10000 + (0x1000 - 1)) & ~(0x1000 - 1)
    ramfsaddr = hex(loadaddr + ramfsoffset)
else:
    ramfsaddr = '-'

bootcmd += ' bootz ' + hex(loadaddr + kernoffset) + ' ' + ramfsaddr + ' ' + hex(loadaddr + dtboffset)

os.system('fdtput -p -t s ' + uboot_dtb + ' /config bootcmd "' + bootcmd + '"')
print(bootcmd)
padder.cat(uboot_dtb)
padder.pad(kernoffset)
padder.cat(zImage)
padder.pad(dtboffset)
padder.cat(zImage_dtb)
if ramfs:
    padder.pad(ramfsoffset)
    padder.cat(ramfs)

outf.close()

os.system('tegrarcm --bct ' + bct + ' --bootloader=' + outfile + ' --loadaddr=' + hex(loadaddr))