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#1
A64 / Realtime scheduling for audio ...
Last post by winfried - October 24, 2026, 01:11:36 PMTrying to setup a streaming station, I found, getting crackled audio with puredata:
"priority 8 scheduling failed" for dsp process and "priority 6 scheduling failed." for GUI...
Test:
Fix the security limits `ulimit -r`-> 0:
- add a group audio, I set the limits in security:
so
But still
With AI help, I found:
Solution: build and installed new kernel from last branch with new config like described in Olimage-guide.pdf:
So the issue is now fixed and working without crackling.
The questions:
Was there a reason for "CONFIG_RT_GROUP_SCHED=y", maybe the stability of the system might be affected or something other does not work ?
Is it this fix save ?
Any hint or discussion about this is welcomed.
Mfg winfried
"priority 8 scheduling failed" for dsp process and "priority 6 scheduling failed." for GUI...
Test:
Code Select
$ ulimit -r
0
$ /usr/bin/chrt -f 8 true
chrt: failed to set pid 0's policy: Operation not permitted
Fix the security limits `ulimit -r`-> 0:
- add a group audio, I set the limits in security:
Code Select
sudo -s
cat > /etc/security/limits.d/99-audio.conf << EOF
@audio - rtprio 20
@audio - memlock unlimited
#@audio - nice -19
EOF
so
Code Select
ulimit -r is now 20, which is correct.But still
Code Select
chrt -f 8 true fails, so I looked in kernel config:Code Select
grep -E 'CONFIG_(CGROUPS|CGROUP_SCHED|RT_GROUP_SCHED|PREEMPT_RT)=|# CONFIG_(CGROUPS|CGROUP_SCHED|RT_GROUP_SCHED|PREEMPT_RT) is not set' "/boot/config-$(uname -r)"
CONFIG_CGROUPS=y
CONFIG_CGROUP_SCHED=y
CONFIG_RT_GROUP_SCHED=y
With AI help, I found:
QuoteCONFIG_RT_GROUP_SCHED=y. With that option, a task in any cgroup other than the root cgroup can only use realtime scheduling if that cgroup has cpu.rt_runtime_us > 0. systemd puts your login session in user.slice/user-1000.slice/session-N.scope, and those cgroups default to 0. The kernel then returns EPERM even though rtprio is 20 in limits.conf
Solution: build and installed new kernel from last branch with new config like described in Olimage-guide.pdf:
Code Select
scripts/config --disable RT_GROUP_SCHED
make olddefconfig
grep RT_GROUP_SCHED .config # should show "is not set"
So the issue is now fixed and working without crackling.
The questions:
Was there a reason for "CONFIG_RT_GROUP_SCHED=y", maybe the stability of the system might be affected or something other does not work ?
Is it this fix save ?
Any hint or discussion about this is welcomed.
Mfg winfried
#2
TERES DIY Laptop / Adrian Black's Turbo VCFMW 202...
Last post by DesSony7 - October 23, 2026, 08:17:19 AM
#3
A64 / Re: Use USB OTG in host mode
Last post by winfried - October 22, 2026, 04:11:20 PMThanks, I understand now. 
#4
A64 / Re: Use USB OTG in host mode
Last post by LubOlimex - October 22, 2026, 02:58:29 PMThe phys property is a software ownership reference, not the physical USB connection.
On A64, PHY0 is shared and dynamically routed:
- Device mode → MUSB
- Host mode → EHCI0/OHCI0
MUSB and the Sun4i PHY driver manage PHY0, VBUS, and role switching. EHCI0/OHCI0 still use PHY0 electrically when it is routed to them, but must not claim it separately because that forces PHY0 permanently into host mode and breaks OTG switching.
This is specific to the A64 chip board which requires different routing (as compared to A20) - PHY0 has to be dual-routed. Fixes are only for the A64 board since the OTG in other Allwinner boards (A20,A13..) works fine. For example A20 uses a different architecture where PHY0 remains attached to MUSB and EHCI/OHCI use separate PHYs.
On A64, PHY0 is shared and dynamically routed:
- Device mode → MUSB
- Host mode → EHCI0/OHCI0
MUSB and the Sun4i PHY driver manage PHY0, VBUS, and role switching. EHCI0/OHCI0 still use PHY0 electrically when it is routed to them, but must not claim it separately because that forces PHY0 permanently into host mode and breaks OTG switching.
This is specific to the A64 chip board which requires different routing (as compared to A20) - PHY0 has to be dual-routed. Fixes are only for the A64 board since the OTG in other Allwinner boards (A20,A13..) works fine. For example A20 uses a different architecture where PHY0 remains attached to MUSB and EHCI/OHCI use separate PHYs.
#5
A64 / Re: Use USB OTG in host mode (...
Last post by winfried - October 22, 2026, 01:12:15 PMConfirmed !
Did update and reboot and there was the mouse and Codec:
Thanx a lot.
Just for understanding:
Why the ehci0: (usb@1c1a000) and ohci0: ( usb@1c1a400) does not need any phys ?
Did update and reboot and there was the mouse and Codec:
Code Select
Bus 004 Device 002: ID 08bb:2902 Texas Instruments PCM2902 Audio Codec
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 002: ID 04b3:310c IBM Corp. Wheel Mouse
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 005 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Thanx a lot.
Just for understanding:
Why the ehci0: (usb@1c1a000) and ohci0: ( usb@1c1a400) does not need any phys ?
#6
A64 / Re: Use USB OTG in host mode
Last post by LubOlimex - October 22, 2026, 10:51:00 AMPatch is now live, run apt update and apt dist-upgrade and let me know how it goes.
#7
A20 / Re: T2-OLinuXino-LIME2-IND are...
Last post by LubOlimex - October 22, 2026, 08:28:59 AMA1 speed card with any size bigger than 8GB. Notice that getting A2 or faster card is not recommended.
It is also recommended to check the card with software tools like f3 (fight flash fraud) or H2testW.
This is mentioned on page 8 of the manual: https://github.com/OLIMEX/OLINUXINO/blob/master/DOCUMENTS/OLIMAGE/Olimage-guide.pdf
It is also recommended to check the card with software tools like f3 (fight flash fraud) or H2testW.
This is mentioned on page 8 of the manual: https://github.com/OLIMEX/OLINUXINO/blob/master/DOCUMENTS/OLIMAGE/Olimage-guide.pdf
#8
A64 / Re: Use USB OTG in host mode
Last post by winfried - October 21, 2026, 10:32:06 PMJust for information:
Just changed what your script does in the dts tree in linux-olimex kernel and installed the compiled dtb files like described in Olimage-guide.pdf:
and it behaved the same way, but changing dr_mode to "host" instead of "otg" did not brought up the host mode after boot, so I wait for the kernel patch.
Just changed what your script does in the dts tree in linux-olimex kernel and installed the compiled dtb files like described in Olimage-guide.pdf:
Code Select
diff --git a/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi b/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
index 29571559e434..68a2d28226d2 100644
--- a/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
+++ b/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
@@ -593,8 +593,8 @@ ehci0: usb@1c1a000 {
<&ccu CLK_USB_OHCI0>;
resets = <&ccu RST_BUS_OHCI0>,
<&ccu RST_BUS_EHCI0>;
- phys = <&usbphy 0>;
- phy-names = "usb";
+ /* phys = <&usbphy 0>; */
+ /* phy-names = "usb"; */
status = "disabled";
};
@@ -605,8 +605,8 @@ ohci0: usb@1c1a400 {
clocks = <&ccu CLK_BUS_OHCI0>,
<&ccu CLK_USB_OHCI0>;
resets = <&ccu RST_BUS_OHCI0>;
- phys = <&usbphy 0>;
- phy-names = "usb";
+ /* phys = <&usbphy 0>; */
+ /* phy-names = "usb"; */
status = "disabled";
};
and it behaved the same way, but changing dr_mode to "host" instead of "otg" did not brought up the host mode after boot, so I wait for the kernel patch.
#9
A20 / Re: T2-OLinuXino-LIME2-IND are...
Last post by saltdelicious - October 21, 2026, 07:03:44 PMJust curious, is there a recommended microSD card capacity for running Olimage Linux smoothly on this board? Also, can the system boot directly from the card without any additional configuration?
#10
ESP32 / Re: Olimax Esp32-POE-ISO
Last post by Klooid - October 21, 2026, 12:27:18 PMThanks for your last message as this helped me to get the device working. Thanks again.