Getting Started Booting the Kernel Using a compressed kernel

Most people will be familiar with compressed kernels from booting Linux on a PC. It is possible to boot a compressed kernel onto the SH4 in the same way, and typically results in the download time dropping to half the time taken for the uncompressed kernel.

To do this a couple of adjustments are needed to the build procedure:

• Make sure the kernel configuration option CONFIG_ZIMAGE_ROM (Processor type and features -> Compressed kernel image in ROM) is not selected.
• Build the kernel using the command: make Image. Note that st40load can only handle ELF executables, so the file to specify on the command line is actually arch/sh/boot/compressed/vmlinux. Trying to use arch/sh/boot/zImage will not work, because this is the binary data only, extracted from the ELF file.
• Finally boot the compressed kernel. Normally the command language procedure BootLinuxKernel is used, however this uses the kernel symbol table to determine where to place the command parameters. As the symbol table no longer available in the compressed kernel, the addresses must be specified directly. To do this call LoadLinuxKernel to load the kernel and set up the kernel parameters, and ConfigureLinuxOptions to set up the kernel command line parameters.

So the complete command line should look something like:

# st40load -t slioch_stb1eval \
  -p "LoadLinuxKernel 0x88001000 arch/sh/boot/compressed/vmlinux ;
      ConfigureLinuxOptions 0x88001000"  -- \
  console=ttySC0,115200 \
  root=/dev/nfs \
  nfsroot=138.198.35.2:/opt/STM/ST40Linux-1.0/devkit/sh4/target \
  ip=138.198.7.101::138.198.1.1:255.255.0.0:iptest101:eth0:off \
  mem=32m