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5c29dbd Apr 17, 2016
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@olofk @stffrdhrn
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Build OpenRISC linux image

Prerequisites

Software

  • Linux source code with OpenRISC patches
  • or1k-elf toolchain
  • or1ksim (optional)
  • or1k-linux toolchain (optional)

Files

  • Device tree file (*.dts, optional)
  • Default Linux configuration (*_defconfig, optional)

Setting up

OpenRISC is officially supported in the Linux kernel since 2011 and can be downloaded from https://www.kernel.org. We do however recommend that you use the kernel from https://github.com/openrisc/linux/ as it contains some convenient features such as a built-in initramfs and extra board configurations for OpenRISC not found in the upstream kernel.

Get Linux source code

git clone https://github.com/openrisc/linux

Set up Linux source code

cd linux
export ARCH=openrisc
export CROSS_COMPILE=or1k-elf-

The device tree file (.dts) is used to specify hardware configuration settings, such as base addresses and interrupt numbers for peripherals, memory sizes, the numbers of CPUs in the system and other things. If no custom device tree is used, a default one is enabled that contains a UART at address 0x90000000, 32MB RAM and one CPU. These parameters should be available for any OpenRISC system and can therefore be safely used. To enable more options, a separate device tree must be used

To add a new device tree

Copy $NAME.dts to arch/openrisc/boot/dts/

(Later, when you run make menuconfig, you can specify your device tree under Processor type and features->Builtin DTB)

The defconfig files is used to customize the Linux kernel for a certain hardware, e.g. enable extra device drivers, networking, filesystems etc. For basic usage it is enough to use the built-in default configuration. This will be enough to boot the kernel and communicate with it through a UART.

To use the built-in default configuration

make defconfig

To use a customized default configuration

Copy $NAME_defconfig to arch/openrisc/configs/

make $NAME_defconfig

To make further customizations

make menuconfig

To build the kernel

make

To load the kernel and start running it in openOCD run

init
reset
halt; load_image vmlinux; reg r3 0; reg npc 0x100; resume

The kernel image is now available as an elf file called vmlinux. This file can be used as any other bare-metal program for OpenRISC. To test the Linux image, you can: