EPICS ioc with RTEMS on Raspberry Pi

[Miroslaw Dach]

Hi All,

I'm running an EPICS ioc server (EPICS 7.0.10)  with RTEMS 6.2 on a
Raspberry Pi 3B+ with rtems-libbsd  (6-freebsd-14) and
encountering a reproducible system hang after several minutes of operation.
Through systematic elimination testing I've narrowed the root cause to the
DWC OTG USB controller driver. I'd appreciate any recommendations on how
to address this. I can of course use the EPICS ioc server under linux on
RPi but just tried to have the RTEMS - Hard real time system which is much
more deterministic.
The boot time for the RPi with EPICS/RTEMS is around 7 sec which is
extremely fast!

Environment
-----------
- Board: Raspberry Pi 3B+ (BCM2837, boardrev a020d3)
- RTEMS: rtems-6.2 (ARM/ARMv4/raspberrypi2)
- Network stack: rtems-libbsd (RTEMS_BSD_CONFIG_BSP_CONFIG +
RTEMS_BSD_CONFIG_INIT)
- Ethernet: LAN7515 USB Ethernet (muge driver, via DWC OTG)
- Application: EPICS IOC (but hang occurs with minimal/empty IOC as well)
- Console: UART serial (/dev/ttyS0)

Symptom
-------
The system boots and runs normally, then the entire system freezes —
including the UART serial console (which is not USB-dependent). No crash
message, no stack dump — a hard hang requiring power cycle.

The time-to-hang depends on the system tick rate:
- CONFIGURE_MICROSECONDS_PER_TICK=500  (2 kHz): hangs after ~2 minutes
- CONFIGURE_MICROSECONDS_PER_TICK=10000 (100 Hz): hangs after ~5-6 minutes

During the hang, the UART becomes completely unresponsive, suggesting a
kernel-level deadlock or interrupt handler issue rather than an
application-level problem.

Elimination testing performed
-----------------------------
I systematically disabled components to isolate the cause. All tests below
used CONFIGURE_MICROSECONDS_PER_TICK=10000 (100 Hz):

1. Disabled all EPICS database records (no record processing) -> still hangs
2. Disabled periodic NTP sync (no socket operations) -> still hangs
3. Disabled IP configuration (no ifconfig, no route, no network traffic,
   but USB/DWC OTG still initialised via RTEMS_BSD_CONFIG_BSP_CONFIG)
   -> still hangs (~5-6 min), USB hub enumeration continues in background:
      ugen1.2: <vendor 0x0424 product 0x2514> at usbus1
      uhub1 on uhub0
      ...
   Console output is garbled by concurrent USB enumeration messages,
   suggesting interrupt contention.
4. Commented out RTEMS_BSD_CONFIG_BSP_CONFIG and the
   #include <bsp/nexus-devices.h> to prevent DWC OTG initialisation
   -> STABLE, ran for 14+ minutes with no hang (test stopped manually)

The libbsd software stack (loopback, sockets, telnetd) continues to
function in test 4 — only the hardware BSP devices (DWC OTG, muge,
uhub, ukphy) are excluded.

Minimal reproduction
--------------------
Build an RTEMS 6.2 application for raspberrypi2 BSP with:

  #define RTEMS_BSD_CONFIG_BSP_CONFIG
  #define RTEMS_BSD_CONFIG_INIT
  #include <machine/rtems-bsd-config.h>
  #include <bsp/nexus-devices.h>     /* in one translation unit */

  #define CONFIGURE_MICROSECONDS_PER_TICK 10000

The application does not need to configure any network interface or
perform any USB transfers — the DWC OTG hub polling alone triggers
the hang after ~5-6 minutes.

Commenting out RTEMS_BSD_CONFIG_BSP_CONFIG and the nexus-devices.h
include eliminates the hang.

Boot log (abbreviated, from hanging configuration)
--------------------------------------------------
RTEMS RPi 3B+ 1.3 (1GB) [00a020d3]
nexus0: <RTEMS Nexus device>
dwcotg0: <DWC OTG 2.0 integrated USB controller> on nexus0
usbus1 on dwcotg0
usbus1: 480Mbps High Speed USB v2.0
ugen1.1: <DWCOTG OTG Root HUB> at usbus1
uhub0 on usbus1
uhub0: <DWCOTG OTG Root HUB, class 9/0, rev 2.00/1.00, addr 1> on usbus1
uhub0: 1 port with 1 removable, self powered
ugen1.2: <vendor 0x0424 product 0x2514> at usbus1
uhub1 on uhub0
uhub1: <vendor 0x0424 product 0x2514, class 9/0, rev 2.00/b.b3, addr 2> on
usbus1
uhub1: 4 ports with 3 removable, self powered
ugen1.3: <vendor 0x0424 product 0x2514> at usbus1
uhub2 on uhub1
uhub2: <vendor 0x0424 product 0x2514, class 9/0, rev 2.00/b.b3, addr 3> on
usbus1
uhub2: 3 ports with 2 removable, self powered
ugen1.4: <vendor 0x0424 product 0x7800> at usbus1
muge0: <vendor 0x0424 product 0x7800, rev 2.10/3.00, addr 4> on usbus1
muge0: Chip ID 0x7800 rev 0002
miibus0: <MII bus> on muge0
ukphy0: <Generic IEEE 802.3u media interface> PHY 1 on miibus0
info: ue0: <USB Ethernet> on muge0
[system hangs after ~5-6 minutes, UART unresponsive]

Questions
---------
1. Is this a known issue with the DWC OTG driver on RPi 3B+?
2. Are there any configuration options (hub polling interval, interrupt
   coalescing, DMA settings) that might work around the problem?
3. Would a newer version of rtems-libbsd contain fixes for this?
4. Is there an alternative Ethernet driver approach for RPi 3B+ that
   avoids the DWC OTG USB path?
5. Is there any known project which uses RPi with RTEMS?
(it looks like that the option to run RTEMS on RPi4 or RPi 5 can not be
considered since the BSP in RTEMS kernel  is not yet finalised.
The RPi4 or RPi 5 would be much better candidates vs RPi 3 B+ since they
use direct connection to Ethernet instead of the USB-Ethernet)

Thank you for any guidance.

Mirek
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.rtems.org/pipermail/users/attachments/20260422/7a0003b8/attachment.htm>