CONFIG_PREEMPT_RT on Raspberry Pi

[twobob]

Aye all good advice.

However having spent many days in the past faffing around with the "wrong" files on other projects it would be nice to know that I am at least starting with the right ones

Thanks for the feedback, I read the entire thread again just in case I missed something.

[clouded]

Hello realtimers,

I build kernels with PREEMPT_RT from time to time and just built the fresh one a couple of days ago - 3.12.36-rt50+.
Links to sources, kernel and SD image are provided below.
Cyclictest results: #Min: 00011uS #Avg: 00023uS #Max: 00066uS

Raspberry Pi linux kernel source patched with rt-patch and config for PREEMPT_RT:
https://github.com/emlid/linux-rt-rpi

Standalone Raspberry Pi linux kernel with modules version 3.12.36-rt50+:
https://mega.co.nz/#!YNRV3RzL!Zvj6-2E8P ... YxYPM5vC5Q

SD card image based on 2014-12-24 Raspbian with 3.12.36-rt50+ kernel and few modifications:
https://mega.co.nz/#!UMZRkJ6Z!4uJF3UTsa ... wIW7Q9WlSc

More information about the image can be found at http://www.emlid.com/new-raspbian-with- ... -jan-2015/.

[clouded]

Hi everyone,

I tried the new 3.18 rt kernels for Raspberry Pi A+\B+ as well as new Raspberry Pi 2.

Kernel for Raspberry Pi A+\B+ seems to work okay.

Kernel for Raspberry Pi 2 has a problem - it freezes without any message (even with debug information enabled) when some process is run on cpu0 with priority <= -51, which is probably caused by the FIQ USB driver. Non-FIQ USB driver does not boot with an error.

If anyone wants to play with rt kernels for old and new RPis here's the patched source code with configs for rt - https://github.com/Clouded/linux-rt-rpi2

[clouded]

I was able to solve the issue that prevented booting with the non-FIQ USB driver. It required the following fix:
https://github.com/Clouded/linux-rt-rpi ... 71a99b283a

Now it is possible to boot with the non-FIQ USB driver by adding these options to the /boot/cmdline.txt :
dwc_otg.fiq_enable=0 dwc_otg.fiq_fsm_enable=0 dwc_otg.nak_holdoff=0

Compiled PREEMPT_RT kernel 3.18 for Raspberry Pi 2 can be downloaded here:
https://mega.co.nz/#!NBhBCSDJ!KSQm9OKU9 ... yexdcg6N1I

Patched source code is available here:
https://github.com/Clouded/linux-rt-rpi2

[mung]

I was able to solve the issue that prevented booting with the non-FIQ USB driver. It required the following fix:
https://github.com/Clouded/linux-rt-rpi ... 71a99b283a

Now it is possible to boot with the non-FIQ USB driver by adding these options to the /boot/cmdline.txt :
dwc_otg.fiq_enable=0 dwc_otg.fiq_fsm_enable=0 dwc_otg.nak_holdoff=0

Compiled PREEMPT_RT kernel 3.18 for Raspberry Pi 2 can be downloaded here:
https://mega.co.nz/#!NBhBCSDJ!KSQm9OKU9 ... yexdcg6N1I

Patched source code is available here:
https://github.com/Clouded/linux-rt-rpi2

Interesting, have you got details of your kernel config?

I compiled for rpi2 with full RT_PREEMPT about a month ago the patch applied totally clean and the kernel booted without problem or error. The cyclictest results (max about 150 min 15us, though my memory is probably a bit poor so could be different) were only marginally better than for a rpi1, but the system never showed any error.

Also what are the cyclictest results with your patched kernel?

[PabloGN]

Hi people.

I didn't found your work before starting the work I describe in http://www.ehu.eus/ehusfera/pablogn/201 ... berry-sbc/

It is a very easy way of kernel building (thanks to Hypriot guys), and it behaves well until stressed with cyclictest and commands like

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ssh user@desktop cat /dev/zero | dd of=/dev/null 

Would you tell me the way to configure? It's maybe the soft irqs, maybe the parameters for cyclictest.

I was able to solve the issue that prevented booting with the non-FIQ USB driver. It required the following fix:
https://github.com/Clouded/linux-rt-rpi ... 71a99b283a

Now it is possible to boot with the non-FIQ USB driver by adding these options to the /boot/cmdline.txt :
dwc_otg.fiq_enable=0 dwc_otg.fiq_fsm_enable=0 dwc_otg.nak_holdoff=0

Compiled PREEMPT_RT kernel 3.18 for Raspberry Pi 2 can be downloaded here:
https://mega.co.nz/#!NBhBCSDJ!KSQm9OKU9 ... yexdcg6N1I

Patched source code is available here:
https://github.com/Clouded/linux-rt-rpi2

Interesting, have you got details of your kernel config?

I compiled for rpi2 with full RT_PREEMPT about a month ago the patch applied totally clean and the kernel booted without problem or error. The cyclictest results (max about 150 min 15us, though my memory is probably a bit poor so could be different) were only marginally better than for a rpi1, but the system never showed any error.

Also what are the cyclictest results with your patched kernel?

[kinsa]

I have patched 4.4 kernels for RPi1/2 available here.

To install for RPi2:

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apt-key adv --keyserver hkp://keys.gnupg.net --recv-key 43DDF224
echo "deb http://deb.machinekit.io/debian raspbian main" > /etc/apt/sources.list.d/machinekit.list
apt-get update
apt-get install -y linux-image-rpi2-rt
cd /boot
echo kernel=$(ls kernel_rt*.img) >> config.txt
echo device_tree=dtbs_rt/bcm2709-rpi-2-b.dtb >> config.txt

For RPi v1, use

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apt-get install -y linux-image-rpi-rt

and adjust device_tree accordingly.

Don't forget to append the following entries to /boot/cmdline.txt:

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dwc_otg.fiq_enable=0 dwc_otg.fiq_fsm_enable=0 dwc_otg.nak_holdoff=0

Sources are located here.

Cheers

Update:
- fixed device_tree entry

[kinsa]

BTW, linux 4.4 needs an updated bootloader, do:

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sudo apt-get update
sudo apt-get install -y raspberrypi-bootloader

[DaveO16]

I've followed these steps with a B+ "Raspberry Pi Model B+ V1.2", ammending dtoverlay in config.txt to
dtoverlay=dtbs_rt/bcm2708-rpi-b-plus.dtb

When I reboot I get a rainbow screen.

if I comment out the "new" kernel in config.txt all is OK.

The image I've installed this on is the most recent.

How do I debug this?

[kinsa]

Can you post your config.txt?

[cjan]

supported 4.4, does it mean 4.4.1~x ?

[DaveO16]

Can you post your config.txt?

Yup, absolutely... thank you for being willing to help...

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$ cat /cygdrive/e/config.txt
# For more options and information see
# http://www.raspberrypi.org/documentation/configuration/config-txt.md
# Some settings may impact device functionality. See link above for details

# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1

# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
#disable_overscan=1

# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
#overscan_left=16
#overscan_right=16
#overscan_top=16
#overscan_bottom=16

# uncomment to force a console size. By default it will be display's size minus
# overscan.
#framebuffer_width=1280
#framebuffer_height=720

# uncomment if hdmi display is not detected and composite is being output
#hdmi_force_hotplug=1

# uncomment to force a specific HDMI mode (this will force VGA)
hdmi_group=2
hdmi_mode=17

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2

# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4

# uncomment for composite PAL
#sdtv_mode=2

#uncomment to overclock the arm. 700 MHz is the default.
arm_freq=900

# Uncomment some or all of these to enable the optional hardware interfaces
#dtparam=i2c_arm=on
#dtparam=i2s=on
#dtparam=spi=on

# Uncomment this to enable the lirc-rpi module
#dtoverlay=lirc-rpi

# Additional overlays and parameters are documented /boot/overlays/README

# Enable audio (loads snd_bcm2835)
dtparam=audio=on
core_freq=250
sdram_freq=450
over_voltage=2
kernel=kernel_rt-4.4.4-rt9+.img
dtoverlay=dtbs_rt/bcm2708-rpi-b-plus.dtb

[PhilE]

This looks wrong:

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dtoverlay=dtbs_rt/bcm2708-rpi-b-plus.dtb

The file is named like a base DTB file (a complete description of the common hardware for a board) but you are loading it like an overlay (a patch to modify a base DTB).

Try this:

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device_tree=dtbs_rt/bcm2708-rpi-b-plus.dtb

[DaveO16]

That worked... time to learn about PREEMPT_RT!

Thank you!