Re: EPICS ioc with RTEMS on Raspberry Pi
Miroslaw Dach <[email protected]> Fri, 8 May 2026 14:59:52 -0700
| Newsgroups | gmane.os.rtems.user |
|---|---|
| Message-ID | <CAPAFRJf5F5mbAZeHpntPnOYjpXkB5JQfQztjJOmAEmwLxUHphA@mail.gmail.com> |
--===============6230280614874093688== Content-Type: multipart/alternative; boundary="000000000000ede19506515584b9" --000000000000ede19506515584b9 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi John, Many Thanks for your reply and all of the hints. It looks like that at present there is no good solution to use RTEMS on RPi 3 b+ due to the issue with the usb-Network bridge. The most promising approach would be to use the PRi v4 or v5 since the network chip is directly connected to the system but the BSP is not yet complete for RTEMS so maybe in the future. Best Regards Mirek sob., 25 kwi 2026 o 10:37 John Howard <[email protected]> napisa=C5=82= (a): > Hi Mirek, > > I don't know what to tell you about this issue. You know more about the > details than I do. > > (I don't know what EPICS IOC does.) > > I knew RTEMS didn't use FIQ, but I assumed a 32/64-bit FreeBSD for > Raspberry Pi didn't either. Why not a continuing FIQ issue on their maili= ng > list after all this time? I haven't used FreeBSD for RPi (too many securi= ty > holes to me). I use Debian Bullseye for my 3B+ and I am not happy with > Linux. > > I don't expect this to occur on RPi Zero 2 W because it lacks the Etherne= t > subsystem and has a newer revision of the 3B+ subsystem. (I will deal wit= h > it later during my app testing phase.) > > I am not the CODEOWNER at RTEMS.org for that Dynaware/Synopsis driver. > > I do know that Synopsis released it unlicensed AS IS but is willing to > license it under obligation for their customers. > > I recently looked at an alternative kernel memory map document where FIQ > stacks are present for RPi 3B+ when Aarch32, but I can't find them when > Aarch64 which standardized calling conventions. > > Sorry I couldn't be of much help to you on this issue. Dealing with FIQ > handling is as idiosyncratic as it gets on Raspberry Pi and is a > deal-breaker to me. > > -- John > > On Apr 22, 2026, at 10:28=E2=80=AFPM, Miroslaw Dach <miroslaw.dach@gmail.= com> > wrote: > > =EF=BB=BF > Hi John, > > Thanks for your e-mail and your suggestion. > > Follow-up to my earlier report about the DWC OTG USB hang on RPi 3B+ > with RTEMS 6. I've done extensive instrumentation and applied BCM2835- > specific errata workarounds from the Linux dwc2 driver. Here are the > complete findings: > > I added diagnostic counters (#ifdef __rtems__) to the FreeBSD dwc_otg > driver, printed every 1 second from the 10ms timer callback: > > - yld: times dwc_otg_interrupt_poll_locked() hit its 16-iteration cap > - afail: times dwc_otg_host_channel_alloc() failed (no free channels) > - hok: successful halt completions processed > - rxd: RX data discarded (no active endpoint listening) > - stuck: channels with wait_halted=3D1 but allocated=3D0 (leaked channels= ) > - filt: filter ISR entry/exit count (to detect stuck ISR) > - thr: thread handler entry/exit count > - gi: last GINTSTS register value > > Results: channel exhaustion theory DISPROVED > Across all tests, every counter remained perfectly healthy right up to > the instant of the freeze: > > DWC_OTG t=3D17500: yld=3D0 afail=3D0 hok=3D180038 rxd=3D0 ch=3D8/16 > alloc=3D0 wh=3D0 stuck=3D0 filt=3D738178/738178 thr=3D7280/7280 > gi=3D0x04000031 > > - yld=3D0: the 16-iteration poll loop cap was NEVER hit > - afail=3D0: channel allocation NEVER failed > - stuck=3D0: NO channels ever leaked (wait_halted was always cleared) > - filt balanced: filter ISR entered and exited the same number of times > - thr balanced: thread handler entered and exited the same number of tim= es > - gi=3D0x04000031: benign (host mode + TX FIFOs empty + RX FIFO non-empty= ) > > The ~1054 halt completions/second were steady with no degradation. > > Results: total CPU freeze, not software deadlock > > I also tried an independent RTEMS timer (rtems_timer_fire_after) as a > heartbeat, firing outside the USB bus lock. Both the USB timer and the > independent heartbeat stopped simultaneously, confirming the entire ARM > core freezes =E2=80=94 not just the USB subsystem. > > No RTEMS fatal error handler was triggered (I installed one via > CONFIGURE_INITIAL_EXTENSIONS). This means it is NOT a standard ARM > data abort =E2=80=94 the CPU simply stops executing, likely due to an AHB= bus > lockup caused by the DWC OTG controller hardware. > > BCM2835 errata workarounds applied > > Based on the Linux dwc2 driver (params.c, core.c) and the Ultibo > project documentation, I applied three workarounds: > > 1. FIFO size cap: BCM2835 hardware reports 4096 words but only 4080 > exist. Cap sc_fifo_size to 4080*4 bytes to prevent FIFO overrun. > (In practice, the hardware on my board reported <=3D 4080, so this > cap was NOT triggered.) > > 2. GAHBCFG AHB burst configuration: Broadcom redefined bits [4:1] of > GAHBCFG for AXI burst control. Linux dwc2 sets ahbcfg=3D0x10 for > BCM2835. Changed from GAHBCFG_GLBLINTRMSK (0x01) to 0x11. > > 3. AHB idle wait after core reset: Added a loop waiting for > GRSTCTL_AHBIDLE after GRSTCTL_CSFTRST, plus 250ms settling delay > (Linux dwc2 uses 100+ ms). > > Results with workarounds: > - Before: hangs after ~86 seconds (2 kHz tick) > - After: hangs after ~175 seconds (2 kHz tick) > > The workarounds approximately doubled the time-to-hang but did NOT > eliminate it. All software counters remained healthy throughout. > > The hang is caused most probably by a combination of factors: > > 1. The DWC OTG controller on BCM2835/BCM2837 requires sub-125=C2=B5s > interrupt response times for USB split transaction phases (Start > Split =E2=86=92 Complete Split through the USB hub). The RPi 3B+ Ether= net > goes through a USB hub (LAN7515), making every packet a split > transaction. > > 2. The Linux kernel addresses this with a dedicated FIQ (Fast Interrupt > Request) handler (dwc_otg_fiq_fsm.c) that executes complete split > transactions in FIQ context, bypassing the normal interrupt stack. > Without FIQ, "certain USB devices become completely unusable." > > 3 The FreeBSD dwc_otg driver used by RTEMS handles all split > transactions in normal interrupt context. On RTEMS, the interrupt > filter and thread handler run back-to-back in the interrupt server > task (nexus_intr_with_filter in rtems-kernel-nexus.c), with no > preemption point between them. > > 4 When the controller's split transaction timing is violated, it > enters an unrecoverable state that locks the AHB bus, freezing the > entire ARM core including UART and system timers. > > The timing correlation with tick rate confirms this: higher tick rate > =3D more frequent scheduling =3D more interrupt latency jitter =3D faster > timing violation. > > A proper fix requires most probably implementing FIQ-based split > transaction handling > in the RTEMS BSP for BCM2835/BCM2837, similar to what Linux does in > dwc_otg_fiq_fsm.c. This is a significant undertaking but is essential > for reliable USB operation on RPi 3B+ (and RPi Zero 2 W, which uses > the same SoC). > > The GAHBCFG and reset sequence workarounds should also be applied as > they improve stability. > > Please give me your thoughts on that. Maybe it is easier to finalise the > BSP for RPi 4 and 5? > > Best Regards > Mirek > > =C5=9Br., 22 kwi 2026 o 13:17 John Howard <[email protected]> napisa= =C5=82(a): > >> Fascinating. Thanks for that detailed report. >> >> You indicated USB enumerating continues running in the background. >> >> I am educated-guessing that a counter maximum is reached, and then >> mistakenly breached. I would look for a test of that counter and correct= it >> from allowing greater-than comparing. >> >> Let us know how it turns out. >> >> I am developing an app for Raspberry Pi Zero 2 W (stripped-down 3B+). I >> wasn't expecting any potential problem like this. >> >> -- John >> >> > On Apr 22, 2026, at 1:25=E2=80=AFPM, Miroslaw Dach <miroslaw.dach@gmai= l.com> >> wrote: >> > >> > =EF=BB=BF >> > 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 h= ow >> > 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 =E2= =80=94 >> > including the UART serial console (which is not USB-dependent). No cra= sh >> > message, no stack dump =E2=80=94 a hard hang requiring power cycle. >> > >> > The time-to-hang depends on the system tick rate: >> > - CONFIGURE_MICROSECONDS_PER_TICK=3D500 (2 kHz): hangs after ~2 minut= es >> > - CONFIGURE_MICROSECONDS_PER_TICK=3D10000 (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=3D10000 (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 traffi= c, >> > 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 =E2=80=94 only the hardware BSP devices (DWC OTG, m= uge, >> > 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 =E2=80=94 the DWC OTG hub polling alone trig= gers >> > 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 usbu= s1 >> > 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, interrup= t >> > 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 b= e >> 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 >> > >> > >> > _______________________________________________ >> > users mailing list >> > [email protected] >> > http://lists.rtems.org/mailman/listinfo/users >> > --000000000000ede19506515584b9 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable <div dir=3D"ltr">Hi John,<div><br></div><div>Many Thanks for your reply and= all of the hints. It looks like that at present=C2=A0there is no good solu= tion=C2=A0to use RTEMS on RPi 3 b+ due to the issue with the<br>usb-Network= bridge. The most promising approach=C2=A0would be to use the PRi v4 or v5= =C2=A0 since the network chip is directly connected to the system but the B= SP is not yet complete for RTEMS so maybe in the future.</div><div><br></di= v><div>Best Regards</div><div>Mirek</div></div><br><div class=3D"gmail_quot= e gmail_quote_container"><div dir=3D"ltr" class=3D"gmail_attr">sob., 25 kwi= 2026 o 10:37=C2=A0John Howard <<a href=3D"mailto:[email protected]= ">[email protected]</a>> napisa=C5=82(a):<br></div><blockquote clas= s=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid r= gb(204,204,204);padding-left:1ex"><div dir=3D"auto"><div dir=3D"ltr"></div>= <div dir=3D"ltr">Hi Mirek,</div><div dir=3D"ltr"><br></div><div dir=3D"ltr"= >I don't know what to tell you about this issue. You know more about th= e details than I do.</div><div dir=3D"ltr"><br></div><div dir=3D"ltr">(I do= n't know what EPICS IOC does.)</div><div dir=3D"ltr"><br></div><div dir= =3D"ltr">I knew RTEMS didn't use FIQ, but I assumed a 32/64-bit FreeBSD= for Raspberry Pi didn't either. Why not a continuing FIQ issue on thei= r mailing list after all this time? I haven't used FreeBSD for RPi (too= many security holes to me). I use Debian Bullseye for my 3B+ and I am not = happy with Linux.</div><div dir=3D"ltr"><br></div><div dir=3D"ltr">I don= 9;t expect this to occur on RPi Zero 2 W because it lacks the Ethernet subs= ystem and has a newer revision of the 3B+ subsystem. (I will deal with it l= ater during my app testing phase.)</div><div dir=3D"ltr"><br></div><div dir= =3D"ltr">I am not the CODEOWNER at RTEMS.org for that Dynaware/Synopsis dri= ver.</div><div dir=3D"ltr"><br></div><div dir=3D"ltr">I do know that Synops= is released it unlicensed AS IS but is willing to license it under obligati= on for their customers.</div><div dir=3D"ltr"><br></div><div dir=3D"ltr">I = recently looked at an alternative kernel memory map document where FIQ stac= ks are present for RPi 3B+ when Aarch32, but I can't find them when Aar= ch64 which standardized calling conventions.</div><div dir=3D"ltr"><br></di= v><div dir=3D"ltr">Sorry I couldn't be of much help to you on this issu= e. Dealing with FIQ handling is as idiosyncratic as it gets on Raspberry Pi= and is a deal-breaker to me.</div><div dir=3D"ltr"><br></div><div dir=3D"l= tr">-- John</div><div dir=3D"ltr"><br><blockquote type=3D"cite">On Apr 22, = 2026, at 10:28=E2=80=AFPM, Miroslaw Dach <<a href=3D"mailto:miroslaw.dac= [email protected]" target=3D"_blank">[email protected]</a>> wrote:<br><b= r></blockquote></div><blockquote type=3D"cite"><div dir=3D"ltr">=EF=BB=BF<d= iv dir=3D"ltr">Hi John,<br><br>Thanks for your e-mail and your suggestion.<= div><br>Follow-up to my earlier report about the DWC OTG USB hang on RPi 3B= +<br>with RTEMS 6. I've done extensive instrumentation and applied BCM2= 835-<br>specific errata workarounds from the Linux dwc2 driver. Here are th= e<br>complete findings:<br><br>I added diagnostic counters (#ifdef __rtems_= _) to the FreeBSD dwc_otg<br>driver, printed every 1 second from the 10ms t= imer callback:<br><br>- yld: =C2=A0 times dwc_otg_interrupt_poll_locked() h= it its 16-iteration cap<br>- afail: times dwc_otg_host_channel_alloc() fail= ed (no free channels)<br>- hok: =C2=A0 successful halt completions processe= d<br>- rxd: =C2=A0 RX data discarded (no active endpoint listening)<br>- st= uck: channels with wait_halted=3D1 but allocated=3D0 (leaked channels)<br>-= filt: =C2=A0filter ISR entry/exit count (to detect stuck ISR)<br>- thr: = =C2=A0 thread handler entry/exit count<br>- gi: =C2=A0 =C2=A0last GINTSTS r= egister value<br><br>Results: channel exhaustion theory DISPROVED<br>Across= all tests, every counter remained perfectly healthy right up to<br>the ins= tant of the freeze:<br><br>=C2=A0 DWC_OTG t=3D17500: yld=3D0 afail=3D0 hok= =3D180038 rxd=3D0 ch=3D8/16<br>=C2=A0 =C2=A0 =C2=A0 alloc=3D0 wh=3D0 stuck= =3D0 filt=3D738178/738178 thr=3D7280/7280<br>=C2=A0 =C2=A0 =C2=A0 gi=3D0x04= 000031<br><br>- yld=3D0: =C2=A0 =C2=A0 the 16-iteration poll loop cap was N= EVER hit<br>- afail=3D0: =C2=A0 channel allocation NEVER failed<br>- stuck= =3D0: =C2=A0 NO channels ever leaked (wait_halted was always cleared)<br>- = filt balanced: filter ISR entered and exited the same number of times<br>- = thr balanced: =C2=A0thread handler entered and exited the same number of ti= mes<br>- gi=3D0x04000031: benign (host mode + TX FIFOs empty + RX FIFO non-= empty)<br><br>The ~1054 halt completions/second were steady with no degrada= tion.<br><br>Results: total CPU freeze, not software deadlock<br><br>I also= tried an independent RTEMS timer (rtems_timer_fire_after) as a<br>heartbea= t, firing outside the USB bus lock. Both the USB timer and the<br>independe= nt heartbeat stopped simultaneously, confirming the entire ARM<br>core free= zes =E2=80=94 not just the USB subsystem.<br><br>No RTEMS fatal error handl= er was triggered (I installed one via<br>CONFIGURE_INITIAL_EXTENSIONS). Thi= s means it is NOT a standard ARM<br>data abort =E2=80=94 the CPU simply sto= ps executing, likely due to an AHB bus<br>lockup caused by the DWC OTG cont= roller hardware.<br><br>BCM2835 errata workarounds applied<br><br>Based on = the Linux dwc2 driver (params.c, core.c) and the Ultibo<br>project document= ation, I applied three workarounds:<br><br>1. FIFO size cap: BCM2835 hardwa= re reports 4096 words but only 4080<br>=C2=A0 =C2=A0exist. Cap sc_fifo_size= to 4080*4 bytes to prevent FIFO overrun.<br>=C2=A0 =C2=A0(In practice, the= hardware on my board reported <=3D 4080, so this<br>=C2=A0 =C2=A0cap wa= s NOT triggered.)<br><br>2. GAHBCFG AHB burst configuration: Broadcom redef= ined bits [4:1] of<br>=C2=A0 =C2=A0GAHBCFG for AXI burst control. Linux dwc= 2 sets ahbcfg=3D0x10 for<br>=C2=A0 =C2=A0BCM2835. Changed from GAHBCFG_GLBL= INTRMSK (0x01) to 0x11.<br><br>3. AHB idle wait after core reset: Added a l= oop waiting for<br>=C2=A0 =C2=A0GRSTCTL_AHBIDLE after GRSTCTL_CSFTRST, plus= 250ms settling delay<br>=C2=A0 =C2=A0(Linux dwc2 uses 100+ ms).<br><br>Res= ults with workarounds:<br>- Before: hangs after ~86 seconds (2 kHz tick)<br= >- After: =C2=A0hangs after ~175 seconds (2 kHz tick)<br><br>The workaround= s approximately doubled the time-to-hang but did NOT<br>eliminate it. All s= oftware counters remained healthy throughout.<br><br>The hang is caused mos= t probably by a combination of factors:<br><br>1. The DWC OTG controller on= BCM2835/BCM2837 requires sub-125=C2=B5s<br>=C2=A0 =C2=A0interrupt response= times for USB split transaction phases (Start<br>=C2=A0 =C2=A0Split =E2=86= =92 Complete Split through the USB hub). The RPi 3B+ Ethernet<br>=C2=A0 =C2= =A0goes through a USB hub (LAN7515), making every packet a split<br>=C2=A0 = =C2=A0transaction.<br><br>2. The Linux kernel addresses this with a dedicat= ed FIQ (Fast Interrupt<br>=C2=A0 =C2=A0Request) handler (dwc_otg_fiq_fsm.c)= that executes complete split<br>=C2=A0 =C2=A0transactions in FIQ context, = bypassing the normal interrupt stack.<br>=C2=A0 =C2=A0Without FIQ, "ce= rtain USB devices become completely unusable."<br><br>3 The FreeBSD dw= c_otg driver used by RTEMS handles all split<br>=C2=A0 =C2=A0transactions i= n normal interrupt context. On RTEMS, the interrupt<br>=C2=A0 =C2=A0filter = and thread handler run back-to-back in the interrupt server<br>=C2=A0 =C2= =A0task (nexus_intr_with_filter in rtems-kernel-nexus.c), with no<br>=C2=A0= =C2=A0preemption point between them.<br><br>4 When the controller's sp= lit transaction timing is violated, it<br>=C2=A0 =C2=A0enters an unrecovera= ble state that locks the AHB bus, freezing the<br>=C2=A0 =C2=A0entire ARM c= ore including UART and system timers.<br><br>The timing correlation with ti= ck rate confirms this: higher tick rate<br>=3D more frequent scheduling =3D= more interrupt latency jitter =3D faster<br>timing violation.</div><div><b= r>A proper fix requires most probably implementing FIQ-based split transact= ion handling<br>in the RTEMS BSP for BCM2835/BCM2837, similar to what Linux= does in<br>dwc_otg_fiq_fsm.c. This is a significant undertaking but is ess= ential<br>for reliable USB operation on RPi 3B+ (and RPi Zero 2 W, which us= es<br>the same SoC).<br><br>The GAHBCFG and reset sequence workarounds shou= ld also be applied as<br>they improve stability.<br><br>Please give me your= thoughts on that. Maybe it is easier to finalise the BSP for RPi 4 and 5?<= br><br>Best Regards<br>Mirek<br></div></div><br><div class=3D"gmail_quote">= <div dir=3D"ltr" class=3D"gmail_attr">=C5=9Br., 22 kwi 2026 o 13:17=C2=A0Jo= hn Howard <<a href=3D"mailto:[email protected]" target=3D"_blank">e= [email protected]</a>> napisa=C5=82(a):<br></div><blockquote class= =3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rg= b(204,204,204);padding-left:1ex">Fascinating. Thanks for that detailed repo= rt.<br> <br> You indicated USB enumerating continues running in the background.<br> <br> I am educated-guessing that a counter maximum is reached, and then mistaken= ly breached. I would look for a test of that counter and correct it from al= lowing greater-than comparing.<br> <br> Let us know how it turns out.<br> <br> I am developing an app for Raspberry Pi Zero 2 W (stripped-down 3B+). I was= n't expecting any potential problem like this.<br> <br> -- John<br> <br> > On Apr 22, 2026, at 1:25=E2=80=AFPM, Miroslaw Dach <<a href=3D"mail= to:[email protected]" target=3D"_blank">[email protected]</a>&g= t; wrote:<br> > <br> > =EF=BB=BF<br> > Hi All,<br> > <br> > I'm running an EPICS ioc server (EPICS 7.0.10)=C2=A0 with RTEMS 6.= 2 on a Raspberry Pi 3B+ with rtems-libbsd=C2=A0 (6-freebsd-14) and<br> > encountering a reproducible system hang after several minutes of opera= tion.<br> > Through systematic elimination testing I've narrowed the root caus= e to the<br> > DWC OTG USB controller driver. I'd appreciate any recommendations = on how<br> > 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 mu= ch more deterministic.<br> > The boot time for the RPi with EPICS/RTEMS is around 7 sec which is ex= tremely fast!<br> > <br> > Environment<br> > -----------<br> > - Board: Raspberry Pi 3B+ (BCM2837, boardrev a020d3)<br> > - RTEMS: rtems-6.2 (ARM/ARMv4/raspberrypi2)<br> > - Network stack: rtems-libbsd (RTEMS_BSD_CONFIG_BSP_CONFIG + RTEMS_BSD= _CONFIG_INIT)<br> > - Ethernet: LAN7515 USB Ethernet (muge driver, via DWC OTG)<br> > - Application: EPICS IOC (but hang occurs with minimal/empty IOC as we= ll)<br> > - Console: UART serial (/dev/ttyS0)<br> > <br> > Symptom<br> > -------<br> > The system boots and runs normally, then the entire system freezes =E2= =80=94<br> > including the UART serial console (which is not USB-dependent). No cra= sh<br> > message, no stack dump =E2=80=94 a hard hang requiring power cycle.<br= > > <br> > The time-to-hang depends on the system tick rate:<br> > - CONFIGURE_MICROSECONDS_PER_TICK=3D500=C2=A0 (2 kHz): hangs after ~2 = minutes<br> > - CONFIGURE_MICROSECONDS_PER_TICK=3D10000 (100 Hz): hangs after ~5-6 m= inutes<br> > <br> > During the hang, the UART becomes completely unresponsive, suggesting = a<br> > kernel-level deadlock or interrupt handler issue rather than an<br> > application-level problem.<br> > <br> > Elimination testing performed<br> > -----------------------------<br> > I systematically disabled components to isolate the cause. All tests b= elow<br> > used CONFIGURE_MICROSECONDS_PER_TICK=3D10000 (100 Hz):<br> > <br> > 1. Disabled all EPICS database records (no record processing) -> st= ill hangs<br> > 2. Disabled periodic NTP sync (no socket operations) -> still hangs= <br> > 3. Disabled IP configuration (no ifconfig, no route, no network traffi= c,<br> >=C2=A0 =C2=A0 but USB/DWC OTG still initialised via RTEMS_BSD_CONFIG_BS= P_CONFIG)<br> >=C2=A0 =C2=A0 -> still hangs (~5-6 min), USB hub enumeration continu= es in background:<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0ugen1.2: <vendor 0x0424 product 0x2514>= ; at usbus1<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0uhub1 on uhub0<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0...<br> >=C2=A0 =C2=A0 Console output is garbled by concurrent USB enumeration m= essages,<br> >=C2=A0 =C2=A0 suggesting interrupt contention.<br> > 4. Commented out RTEMS_BSD_CONFIG_BSP_CONFIG and the<br> >=C2=A0 =C2=A0 #include <bsp/nexus-devices.h> to prevent DWC OTG i= nitialisation<br> >=C2=A0 =C2=A0 -> STABLE, ran for 14+ minutes with no hang (test stop= ped manually)<br> > <br> > The libbsd software stack (loopback, sockets, telnetd) continues to<br= > > function in test 4 =E2=80=94 only the hardware BSP devices (DWC OTG, m= uge,<br> > uhub, ukphy) are excluded.<br> > <br> > Minimal reproduction<br> > --------------------<br> > Build an RTEMS 6.2 application for raspberrypi2 BSP with:<br> > <br> >=C2=A0 =C2=A0#define RTEMS_BSD_CONFIG_BSP_CONFIG<br> >=C2=A0 =C2=A0#define RTEMS_BSD_CONFIG_INIT<br> >=C2=A0 =C2=A0#include <machine/rtems-bsd-config.h><br> >=C2=A0 =C2=A0#include <bsp/nexus-devices.h>=C2=A0 =C2=A0 =C2=A0/*= in one translation unit */<br> > <br> >=C2=A0 =C2=A0#define CONFIGURE_MICROSECONDS_PER_TICK 10000<br> > <br> > The application does not need to configure any network interface or<br= > > perform any USB transfers =E2=80=94 the DWC OTG hub polling alone trig= gers<br> > the hang after ~5-6 minutes.<br> > <br> > Commenting out RTEMS_BSD_CONFIG_BSP_CONFIG and the nexus-devices.h<br> > include eliminates the hang.<br> > <br> > Boot log (abbreviated, from hanging configuration)<br> > --------------------------------------------------<br> > RTEMS RPi 3B+ 1.3 (1GB) [00a020d3]<br> > nexus0: <RTEMS Nexus device><br> > dwcotg0: <DWC OTG 2.0 integrated USB controller> on nexus0<br> > usbus1 on dwcotg0<br> > usbus1: 480Mbps High Speed USB v2.0<br> > ugen1.1: <DWCOTG OTG Root HUB> at usbus1<br> > uhub0 on usbus1<br> > uhub0: <DWCOTG OTG Root HUB, class 9/0, rev 2.00/1.00, addr 1> o= n usbus1<br> > uhub0: 1 port with 1 removable, self powered<br> > ugen1.2: <vendor 0x0424 product 0x2514> at usbus1<br> > uhub1 on uhub0<br> > uhub1: <vendor 0x0424 product 0x2514, class 9/0, rev 2.00/b.b3, add= r 2> on usbus1<br> > uhub1: 4 ports with 3 removable, self powered<br> > ugen1.3: <vendor 0x0424 product 0x2514> at usbus1<br> > uhub2 on uhub1<br> > uhub2: <vendor 0x0424 product 0x2514, class 9/0, rev 2.00/b.b3, add= r 3> on usbus1<br> > uhub2: 3 ports with 2 removable, self powered<br> > ugen1.4: <vendor 0x0424 product 0x7800> at usbus1<br> > muge0: <vendor 0x0424 product 0x7800, rev 2.10/3.00, addr 4> on = usbus1<br> > muge0: Chip ID 0x7800 rev 0002<br> > miibus0: <MII bus> on muge0<br> > ukphy0: <Generic IEEE 802.3u media interface> PHY 1 on miibus0<b= r> > info: ue0: <USB Ethernet> on muge0<br> > [system hangs after ~5-6 minutes, UART unresponsive]<br> > <br> > Questions<br> > ---------<br> > 1. Is this a known issue with the DWC OTG driver on RPi 3B+?<br> > 2. Are there any configuration options (hub polling interval, interrup= t<br> >=C2=A0 =C2=A0 coalescing, DMA settings) that might work around the prob= lem?<br> > 3. Would a newer version of rtems-libbsd contain fixes for this?<br> > 4. Is there an alternative Ethernet driver approach for RPi 3B+ that<b= r> >=C2=A0 =C2=A0 avoids the DWC OTG USB path?<br> > 5. Is there any known project which uses RPi with RTEMS?<br> > (it looks like that the option to run RTEMS on RPi4 or RPi 5 can not b= e considered since the BSP in RTEMS kernel=C2=A0 is not yet finalised.<br> > The RPi4 or RPi 5 would be much better candidates vs RPi 3 B+ since th= ey use direct connection to Ethernet instead of the USB-Ethernet) <br> > <br> > Thank you for any guidance.<br> > <br> > Mirek<br> > <br> > <br> > _______________________________________________<br> > users mailing list<br> > <a href=3D"mailto:[email protected]" target=3D"_blank">[email protected]</= a><br> > <a href=3D"http://lists.rtems.org/mailman/listinfo/users" rel=3D"noref= errer" target=3D"_blank">http://lists.rtems.org/mailman/listinfo/users</a><= br> </blockquote></div> </div></blockquote></div></blockquote></div> --000000000000ede19506515584b9-- --===============6230280614874093688== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ users mailing list [email protected] http://lists.rtems.org/mailman/listinfo/users --===============6230280614874093688==--