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openSUSE:ARM Tech Symposia 2014/STM32F429

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As demonstration of openSUSE 13.2 development tools for ARM and on ARM, Andreas Färber presented a project from SUSE Hackweek Interstellar: Linux running on the STM32F4 microcontroller.


The STM32F4 Discovery kit for STM32F429 was kindly provided by Rutronik.

  • STM32F429ZIT6 microcontroller
    • ARM Cortex-M4F at 180 MHz
    • 2 MB of internal flash
    • 256 KB of internal SRAM
  • 8 MB of on-board SDRAM

New at ARM Tech Symposium

What was new about the demo at ARM Tech Symposium Europe is the kernel. It was originally based on v3.18-rc5, later rebased onto v3.18-rc6, and used the new Device Tree concept to describe the hardware.

The following minimal set of kernel drivers was implemented:

  • USART3 earlyprintk support
  • SysTick clock source
  • RCC clock controller
  • TIM2 clock events
  • USART3 serial console
  • LTDC framebuffer

Not implemented were, among others:

  • GPIO controller (relying on bootloader)
  • RCC reset controller (using ad-hoc reset code instead)
  • DMA for serial
  • DMA2D framebuffer acceleration
  • LTDC initialization (relying on bootloader)
  • RTC
  • USB

The U-Boot bootloader was taken from here and only modified to load the kernel from a different flash address and to pass the device tree flash address to the kernel.


The genromfs package from home:a_faerber:arm was deleted, as it is available in Base:System already.

The latest kernel work rebased onto v3.19-rc1 is here:

  • reset driver for RCC (WIP)

Initial U-Boot bootloader work is here, not yet fully building. Also see "[U-Boot] [PATCH v2] arm: build arch memset/memcpy in Thumb2 mode" on the U-Boot mailing list.

As alternative, a non-interactive custom bootloader has been made available. It uses less than 2 KB of flash, freeing some more space for kernel and device tree.


Flash layout

Start End Size Used Contents
0x08000000 0x0801FFFF 128 KB 75048 B U-Boot bootloader
0x08020000 0x08020FFF 4096 B 3017 B Flat device tree
0x08021000 0x0811FFFF 1 MB minus 4096 B 1025908 B Linux kernel (XIP)
0x08120000 0x081FFFFF 1 MB minus 128 KB 293888 B ROMFS filesystem with busybox

Note: Due to flash erase size restrictions, the kernel and device tree needed to be flashed together.


openocd -f board/stm32f429discovery.cfg \
        -c "init" \
        -c "reset init" \
        -c "flash probe 0" \
        -c "flash info 0" \
        -c "flash write_image erase dtb+uImage.bin 0x08020000" \
        -c "reset run" \
        -c "shutdown"


Compiler for kernel: gcc 4.8-6.1 / gcc48 4.8.3+r212056-5.1 from openSUSE Factory

$ gcc --version
gcc (SUSE Linux) 4.8.3 20140627 [gcc-4_8-branch revision 212064]
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO

Assembler for kernel: binutils 2.24-5.1 from openSUSE Factory

$ as --version
GNU assembler (GNU Binutils; openSUSE Factory)
Copyright 2013 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or later.
This program has absolutely no warranty.
This assembler was configured for a target of `armv7hl-suse-linux-gnueabi'.

Flasher and on-chip debugger: openocd 0.8.0-4.1 from openSUSE Factory

$ openocd --version
Open On-Chip Debugger 0.8.0 (2014-10-11-17:40)
Licensed under GNU GPL v2
For bug reports, read

Debugger: gdb 7.8-4.1 from openSUSE Factory

$ gdb --version
GNU gdb (GDB; openSUSE Factory) 7.8
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "armv7hl-suse-linux".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
Find the GDB manual and other documentation resources online at:
For help, type "help".
Type "apropos word" to search for commands related to "word".

File system creation: genromfs 0.5.2-95.1.2 from openSUSE 13.2 (on x86_64)

$ genromfs -h
genromfs 0.5.2
Usage: genromfs [OPTIONS] -f IMAGE
Create a romfs filesystem image from a directory

  -f IMAGE               Output the image into this file
  -d DIRECTORY           Use this directory as source
  -v                     (Too) verbose operation
  -V VOLUME              Use the specified volume name
  -a ALIGN               Align regular file data to ALIGN bytes
  -A ALIGN,PATTERN       Align all objects matching pattern to at least ALIGN bytes
  -x PATTERN             Exclude all objects matching pattern
  -h                     Show this help


U-Boot 2010.03-00003-g934021a-dirty (Nov 29 2014 - 02:04:13)

CPU  : STM32F4 (Cortex-M4)
Freqs: SYSCLK=180MHz,HCLK=180MHz,PCLK1=45MHz,PCLK2=90MHz
Board: STM32F429I-DISCOVERY board,Rev 1.0
DRAM:   8 MB
Using default environment

Hit any key to stop autoboot:  0 
## Booting kernel from Legacy Image at 08021000 ...
   Image Name:   Linux-3.18
   Image Type:   ARM Linux Kernel Image (uncompressed)
   Data Size:    1025844 Bytes = 1001.8 kB
   Load Address: 08021040
   Entry Point:  08021041
   Verifying Checksum ... OK
   Loading Kernel Image ... OK

Starting kernel ...

Booting Linux on physical CPU 0x0
Linux version 3.18.0-rc6-00016-g4c00142-dirty (andreas@droide) (gcc version 4.8.3 20140627 [gcc-4_8-branch revision 212064] (SUSE Linux) ) #165 Mon Dec 1 04:27:08 CET 2014
CPU: ARMv7-M [410fc241] revision 1 (ARMv7M), cr=00000000
CPU: unknown data cache, unknown instruction cache
Machine model: ST STM32F4 Discovery kit for STM32F429
bootconsole [earlycon0] enabled
debug: ignoring loglevel setting.
On node 0 totalpages: 2048
free_area_init_node: node 0, pgdat 9001fb60, node_mem_map 906f0000
  Normal zone: 16 pages used for memmap
  Normal zone: 0 pages reserved
  Normal zone: 2048 pages, LIFO batch:0
pcpu-alloc: s0 r0 d32768 u32768 alloc=1*32768
pcpu-alloc: [0] 0 
Built 1 zonelists in Zone order, mobility grouping off.  Total pages: 2032
Kernel command line: console=ttystm3,115200n8 earlyprintk ignore_loglevel debug clk_ignore_unused ihash_entries=64 dhash_entries=64 uclinux.physaddr=0x08120000 root=/dev/mtdblock0 rdinit=/sbin/init
PID hash table entries: 32 (order: -5, 128 bytes)
Dentry cache hash table entries: 64 (order: -4, 256 bytes)
Inode-cache hash table entries: 64 (order: -4, 256 bytes)
Memory: 6904K/8192K available (758K kernel code, 76K rwdata, 104K rodata, 60K init, 55K bss, 1288K reserved)
Virtual kernel memory layout:
    vector  : 0x00000000 - 0x00001000   (   4 kB)
    fixmap  : 0xffc00000 - 0xffe00000   (2048 kB)
    vmalloc : 0x00000000 - 0xffffffff   (4095 MB)
    lowmem  : 0x90000000 - 0x90800000   (   8 MB)
      .text : 0x08021040 - 0x080f8928   ( 863 kB)
      .init : 0x9000a000 - 0x9000f000   (  20 kB)
      .data : 0x90008000 - 0x90020200   (  97 kB)
       .bss : 0x90020200 - 0x9002debc   (  56 kB)
NR_IRQS:16 nr_irqs:16 16
rcc @ 0x40023800
clk HSI @ 16000000
clk HSE @ 8000000
clk PLLSRC @ 8000000
clk PLL @ 360000000
clk PLLCLK @ 180000000
clk PLL48CK @ 51428572
clk SYSCLK @ 180000000
clk AHB @ 180000000
clk APB1 @ 45000000
clk TIM2 @ 45000000
clk TIM3 @ 45000000
clk TIM4 @ 45000000
clk TIM5 @ 45000000
clk USART3 @ 45000000
clk APB2 @ 90000000
timer @ 0x40000000 (90000000)
before TIMx CR1 (40000000)
before TIMx CR1 (40000000)
systick @ 0xe000e010 (22500000)
sched_clock: 32 bits at 100 Hz, resolution 10000000ns, wraps every 21474836480000000ns
Console: colour dummy device 80x30
Calibrating delay loop... 118.68 BogoMIPS (lpj=593408)
pid_max: default: 32768 minimum: 301
Mount-cache hash table entries: 1024 (order: 0, 4096 bytes)
Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes)
devtmpfs: initialized
Switched to clocksource cortex-m3-systick
futex hash table entries: 256 (order: -1, 3072 bytes)
romfs: ROMFS MTD (C) 2007 Red Hat, Inc.
Block layer SCSI generic (bsg) driver version 0.4 loaded (major 254)
io scheduler noop registered
io scheduler deadline registered (default)
Console: switching to colour frame buffer device 30x40
stm32_usart 40004800.uart: ttystm3 at MMIO 0x40004800 (irq = 17, base_baud = 0) is a stm32_usart
console [ttystm3] enabled
bootconsole [earlycon0] disabled
brd: module loaded
uclinux[mtd]: probe address=0x8120000 size=0x48000
Creating 1 MTD partitions on "rom":
0x000000000000-0x000000048000 : "ROMfs"
clk: Not disabling unused clocks
VFS: Mounted root (romfs filesystem) readonly on device 31:0.
devtmpfs: mounted
Freeing unused kernel memory: 20K (9000a000 - 9000f000)
starting pid 23, tty '/dev/ttystm3': '/bin/login -f root'
Welcome to
          ____ _  _
         /  __| ||_|                 
    _   _| |  | | _ ____  _   _  _  _ 
   | | | | |  | || |  _ \| | | |\ \/ /
   | |_| | |__| || | | | | |_| |/    \
   |  ___\____|_||_|_| |_|\____|\_/\_/
   | |

For further information check:

Jan  1 00:00:00 login[23]: root login on 'ttystm3'
~ #
~ # cat /proc/cpuinfo
processor       : 0
model name      : ARMv7-M rev 1 (v7ml)
Features        : half thumb fastmult idivt 
CPU implementer : 0x41
CPU architecture: 7M
CPU variant     : 0x0
CPU part        : 0xc24
CPU revision    : 1

Hardware        : STM32 (Device Tree Support)
Revision        : 0000
Serial          : 0000000000000000
~ # cat /proc/meminfo 
MemTotal:           6924 kB
MemFree:            3752 kB
MemAvailable:       3664 kB
Buffers:             264 kB
Cached:              296 kB
SwapCached:            0 kB
Active:              508 kB
Inactive:             32 kB
Active(anon):          0 kB
Inactive(anon):        0 kB
Active(file):        508 kB
Inactive(file):       32 kB
Unevictable:           0 kB
Mlocked:               0 kB
MmapCopy:            824 kB
SwapTotal:             0 kB
SwapFree:              0 kB
Dirty:                 0 kB
Writeback:             0 kB
AnonPages:             0 kB
Mapped:                0 kB
Shmem:                 0 kB
Slab:                612 kB
SReclaimable:        100 kB
SUnreclaim:          512 kB
KernelStack:         136 kB
PageTables:            0 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:        3460 kB
Committed_AS:          0 kB
VmallocTotal:          0 kB
VmallocUsed:           0 kB
VmallocChunk:          0 kB
~ # cat /proc/iomem 
90000000-907fffff : System RAM
  90008000-9002debb : Kernel data
~ # busybox
BusyBox v1.22.1 (2014-11-29 03:23:08 CET) multi-call binary.
BusyBox is copyrighted by many authors between 1998-2012.
Licensed under GPLv2. See source distribution for detailed
copyright notices.

Usage: busybox [function [arguments]...]
   or: busybox --list
   or: function [arguments]...

        BusyBox is a multi-call binary that combines many common Unix
        utilities into a single executable.  Most people will create a
        link to busybox for each function they wish to use and BusyBox
        will act like whatever it was invoked as.

Currently defined functions:
        bash, cat, chgrp, chmod, chown, chroot, clear, cp, date, dd, df, dmesg,
        du, fbset, free, freeramdisk, fuser, getty, halt, hd, head, hexdump,
        hush, init, insmod, iostat, kill, killall, killall5, less, ln, login,
        ls, lsmod, md5sum, mkdir, mkdosfs, mke2fs, mkfs.ext2, mkfs.vfat, mknod,
        modinfo, more, mount, mv, passwd, pgrep, pidof, pkill, poweroff, ps,
        pstree, pwd, reboot, renice, reset, rm, rmdir, rmmod, sh, sleep, stat,
        sync, sysctl, tail, time, top, umount, uname, uptime, vi, watch