More details on Fedora on a Beagleboard

It seems to be advised to build your own kernel for an ARM board. I have no idea yet if some kind of default kernel would (suboptimal) work, so I built a more fine-tuned kernel for the beagleboard. Luckily there was a default configuration for a beagleboard (make beagleboard_defconfig), sadly that default is not available in current kernels anymore. taking an old config and updating it a little, got me a recent kernel (2.6.38-rc3) that seems to work on the beagleboard.

After some more research through the kernel logs, it seems that the beagleboard_defconfig was renamed several times, currently it is available as omap2plus_defconfig. I probably need to build a new kernel now... Unfortunately it takes quite a while to build a new kernel on an emulated ARM board (I'm not into crosscompiling with a recent gcc version yet). The SD card I have is a little small, putting both the root filesystem and the kernel-sources on it seems difficult, an exercise I'll experiment with later.

The beagleboard uses u-boot as bootlader, and I have not found out how to use a initial RAM disk. This has not been an issue yet, as I did not feel like creating an initial RAM disk by hand. Fedora comes with dracut that can generate one for me, so why bother?

The current kernel has all requirements built-in. There is no need for an initial RAM disk. Well, actually there is... init seems to require the /proc fileystem mounted, if it is not mounted, init decides to reboot the system as there are some process-communication issues. Starting with an emergency shell (pass init=/bin/dash on the commandline) allows me to manually mount /proc (even if it claims to be mounted already).

Compared to an older version of the kernel, this kernel offers options to enable optimized OMAP-serial ports:
With these options enabled, the standard /dev/ttyS2 does not seem to provide any output. Instead it seems to be required to use the OMAP-specific /dev/ttyO2 (that's an 'O' for Oscar, not a '0' as zero).

My final u-boot defaults (saved with saveenv) looks like this:
OMAP3 # printenv
bootargs=console=ttyO2,115200n8 root=/dev/mmcblk0p2 ro rootwait init=/bin/dash
bootcmd=mmcinit ; fatload mmc 0:1 0x80000000 uimage-2.6.38-rc3.beagleboard_201102131201 ; bootm 0x80000000

Environment size: 267/131068 bytes

Booting the system and starting dash as directed by the init parameter can be done as follows:
OMAP3 # boot
## Booting kernel from Legacy Image at 80000000 ...
Image Name: Linux-2.6.38-rc3.beagleboard
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 1751256 Bytes = 1.7 MB
Load Address: 80008000
Entry Point: 80008000
Verifying Checksum ... OK
Loading Kernel Image ... OK

Starting kernel ...

Uncompressing Linux... done, booting the kernel.
Linux version 2.6.38-rc3.beagleboard (root@fedora-arm) (gcc version 4.4.2 20091019 (Red Hat 4.4.2-5) (GCC) ) #2 Sun Feb 13 22:26:07 EST 2011
CPU: ARMv7 Processor [411fc082] revision 2 (ARMv7), cr=10c53c7f
CPU: VIPT nonaliasing data cache, VIPT nonaliasing instruction cache
Machine: OMAP3 Beagle Board
Memory policy: ECC disabled, Data cache writeback
OMAP3430/3530 ES2.1 (l2cache iva sgx neon isp )
SRAM: Mapped pa 0x40200000 to va 0xfe400000 size: 0x10000
Built 1 zonelists in Zone order, mobility grouping on. Total pages: 32512
Kernel command line: console=ttyO2,115200n8 root=/dev/mmcblk0p2 ro rootwait init=/bin/dash
PID hash table entries: 512 (order: -1, 2048 bytes)
Dentry cache hash table entries: 16384 (order: 4, 65536 bytes)
Inode-cache hash table entries: 8192 (order: 3, 32768 bytes)
Memory: 128MB = 128MB total
Memory: 126296k/126296k available, 4776k reserved, 0K highmem
Virtual kernel memory layout:
vector : 0xffff0000 - 0xffff1000 ( 4 kB)
fixmap : 0xfff00000 - 0xfffe0000 ( 896 kB)
DMA : 0xffc00000 - 0xffe00000 ( 2 MB)
vmalloc : 0xc8800000 - 0xf8000000 ( 760 MB)
lowmem : 0xc0000000 - 0xc8000000 ( 128 MB)
modules : 0xbf000000 - 0xc0000000 ( 16 MB)
.init : 0xc0008000 - 0xc002b000 ( 140 kB)
.text : 0xc002b000 - 0xc033d000 (3144 kB)
.data : 0xc033e000 - 0xc0369480 ( 174 kB)
Clocking rate (Crystal/Core/MPU): 26.0/332/500 MHz
Reprogramming SDRC clock to 332000000 Hz
GPMC revision 5.0
IRQ: Found an INTC at 0xfa200000 (revision 4.0) with 96 interrupts
Total of 96 interrupts on 1 active controller
OMAP clockevent source: GPTIMER12 at 32768 Hz
sched_clock: 32 bits at 32kHz, resolution 30517ns, wraps every 131071999ms
Console: colour dummy device 80x30
Calibrating delay loop... 471.61 BogoMIPS (lpj=1843200)
pid_max: default: 32768 minimum: 301
Mount-cache hash table entries: 512
CPU: Testing write buffer coherency: ok
print_constraints: dummy:
NET: Registered protocol family 16
omap_device: omap_gpio.0: new worst case activate latency 0: 30517
OMAP GPIO hardware version 2.5
OMAP GPIO hardware version 2.5
OMAP GPIO hardware version 2.5
OMAP GPIO hardware version 2.5
OMAP GPIO hardware version 2.5
OMAP GPIO hardware version 2.5
omap_mux_init: Add partition: #1: core, flags: 0
OMAP3 Beagle Rev: unknown 3
omap_device: omap_uart.0: new worst case activate latency 0: 30517
omap_device: omap_uart.0: new worst case deactivate latency 0: 30517
Found NAND on CS0
Registering NAND on CS0
Unable to get DVI reset GPIO
OMAP DMA hardware revision 4.0
bio: create slab at 0
SCSI subsystem initialized
omap_device: omap_i2c.1: new worst case activate latency 0: 30517
omap_i2c omap_i2c.1: bus 1 rev3.12 at 2600 kHz
twl4030: PIH (irq 7) chaining IRQs 368..375
twl4030: power (irq 373) chaining IRQs 376..383
twl4030: gpio (irq 368) chaining IRQs 384..401
print_constraints: VUSB1V5: 1500 mV normal standby
print_constraints: VUSB1V8: 1800 mV normal standby
print_constraints: VUSB3V1: 3100 mV normal standby
twl4030_usb twl4030_usb: Initialized TWL4030 USB module
print_constraints: VMMC1: 1850 <--> 3150 mV at 3000 mV normal standby
print_constraints: VDAC: 1800 mV normal standby
print_constraints: VDVI: 1800 mV normal standby
print_constraints: VSIM: 1800 <--> 3000 mV at 1800 mV normal standby
omap_i2c omap_i2c.3: bus 3 rev3.12 at 100 kHz
Switching to clocksource 32k_counter
Switched to NOHz mode on CPU #0
musb-hdrc: version 6.0, tusb-omap-dma, peripheral, debug=0
NET: Registered protocol family 2
IP route cache hash table entries: 1024 (order: 0, 4096 bytes)
TCP established hash table entries: 4096 (order: 3, 32768 bytes)
TCP bind hash table entries: 4096 (order: 2, 16384 bytes)
TCP: Hash tables configured (established 4096 bind 4096)
TCP reno registered
UDP hash table entries: 256 (order: 0, 4096 bytes)
UDP-Lite hash table entries: 256 (order: 0, 4096 bytes)
NET: Registered protocol family 1
RPC: Registered udp transport module.
RPC: Registered tcp transport module.
RPC: Registered tcp NFSv4.1 backchannel transport module.
NetWinder Floating Point Emulator V0.97 (double precision)
JFFS2 version 2.2. (NAND) © 2001-2006 Red Hat, Inc.
msgmni has been set to 246
io scheduler noop registered
io scheduler deadline registered
io scheduler cfq registered (default)
Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
omap_uart.0: ttyO0 at MMIO 0x4806a000 (irq = 72) is a OMAP UART0
omap_uart.1: ttyO1 at MMIO 0x4806c000 (irq = 73) is a OMAP UART1
omap_uart.2: ttyO2 at MMIO 0x49020000 (irq = 74) is a OMAP UART2
console [ttyO2] enabled
brd: module loaded
loop: module loaded
twl_rtc twl_rtc: rtc core: registered twl_rtc as rtc0
omap_device: omap_i2c.1: new worst case deactivate latency 0: 30517
i2c /dev entries driver
sdhci: Secure Digital Host Controller Interface driver
sdhci: Copyright(c) Pierre Ossman
TCP cubic registered
NET: Registered protocol family 17
NET: Registered protocol family 15
VFP support v0.3: implementor 41 architecture 3 part 30 variant c rev 1
omap_voltage_late_init: Unable to create voltage debugfs main dir
vdd_debugfs_init: Unable to create debugfs directory for vdd_mpu
vdd_debugfs_init: Unable to create debugfs directory for vdd_core
Power Management for TI OMAP3.
regulator_init_complete: VDVI: incomplete constraints, leaving on
regulator_init_complete: VDAC: incomplete constraints, leaving on
twl_rtc twl_rtc: setting system clock to 2000-01-01 00:03:14 UTC (946684994)
Waiting for root device /dev/mmcblk0p2...
mmc0: new SD card at address 9ced
mmcblk0: mmc0:9ced SD02G 1.89 GiB
mmcblk0: p1 p2
EXT3-fs: barriers not enabled
kjournald starting. Commit interval 5 seconds
EXT3-fs (mmcblk0p2): mounted filesystem with writeback data mode
VFS: Mounted root (ext3 filesystem) readonly on device 179:2.
Freeing init memory: 140K
/bin/dash: can't access tty; job control turned off

The way to boot into a multi-user system (or change the runlevel so something else) was the following:
# mount /proc
# mount /sys
# exec init
Unfortunately it looks as if upstart or udev from Fedora 12 does not recognise the /dev/ttyO* as serial console. Of course I do not have the possibility (hte beagleboard has, just I do not) to connect a monitor over HDMI or S-video and serial-console is the only working output available. Yet another thing to look into some other day.
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