Ok, I have a more localized test that triggers the exception:
https://github.com/PocketNC/cloud9-examples/blob/test-pru-gpio-access/BeagleBone/AI/pru/doNothingToGPIO8.pru1_1.c

Two stack traces can be seen in dmesg after running that on the PRU. If it
has something to do with the device tree, this is the overlay I'm using:
https://github.com/PocketNC/BeagleBoard-DeviceTrees/blob/pocketnc-ai-test/src/arm/am5729-beagleboneai-pocketnc-pro.dts

On Tue, Apr 28, 2020 at 1:20 PM John Allwine <[email protected]> wrote:

> Are there any ramifications of the PRU writing 0 to both the set and clear
> addresses of GPIO8 (0x48053190 and 0x48053194), when the device tree has
> several overlapping pins allocated to being direct outputs on the PRU? The
> issue seems to arise when I write to those two addresses on the PRU, as
> well as the set and clear addresses of GPIO4 (0x48059190 and 0x48059194).
> What could cause that to trigger an exception in the kernel?
>
> On Tue, Apr 28, 2020 at 12:19 PM John Allwine <[email protected]> wrote:
>
>> It seems that even if I hardcode the addresses in there (to eliminate the
>> possibility that my registers were getting overwritten somewhere), that I
>> get the bus error.  Does enabling the OCP Master port work the same way as
>> on the BBB? It's supposedly being set here:
>> https://github.com/PocketNC/machinekit-hal/blob/c8b38386d87abc45baa33593681cbae46d996980/src/hal/drivers/hal_pru_generic/pru_generic.p#L174-L176
>>
>> On Tue, Apr 28, 2020 at 11:47 AM John Allwine <[email protected]> wrote:
>>
>>> It's the hal_pru_generic code. It definitely smells like a bus error. In
>>> fact, if I comment out the lines that write to the GPIO, it stops
>>> happening, so it seems like I have the wrong addresses in there, but I'm
>>> struggling figuring out how that could be.
>>>
>>> These lines are where the GPIO ports are written to in memory:
>>>
>>> https://github.com/PocketNC/machinekit-hal/blob/c8b38386d87abc45baa33593681cbae46d996980/src/hal/drivers/hal_pru_generic/pru_wait.p#L214-L217
>>>
>>> Theoretically, the addresses should be set to the clear addresses of
>>> GPIO3, GPIO5, GPIO6 and GPIO7:
>>>
>>> Addresses defined here:
>>>
>>> https://github.com/PocketNC/machinekit-hal/blob/c8b38386d87abc45baa33593681cbae46d996980/src/hal/support/pru/pru.h#L303-L307
>>>
>>> Loaded into registers here:
>>>
>>> https://github.com/PocketNC/machinekit-hal/blob/c8b38386d87abc45baa33593681cbae46d996980/src/hal/drivers/hal_pru_generic/pru_generic.p#L261-L264
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> On Tue, Apr 28, 2020 at 10:50 AM Jason Kridner <[email protected]>
>>> wrote:
>>>
>>>> What is the code running on PRUSS2 PRU1?
>>>>
>>>> This line kinda spells out an illegal access by that PRU or of that PRU:
>>>> MASTER PRUSS2 PRU1 TARGET L4_PER1_P3 (Idle): Data Access in Supervisor
>>>> mode during Functional access
>>>>
>>>> Looks like the error is from here:
>>>> https://github.com/beagleboard/linux/blob/7a920684860a790099061b67961d0b5ffa033fdf/drivers/bus/omap_l3_noc.c#L135
>>>>
>>>> Looks like a bus exception to me.
>>>>
>>>> On Tue, Apr 28, 2020 at 11:46 AM <[email protected]> wrote:
>>>>
>>>>> I'm getting this stack trace in dmesg, but I'm unsure what it means or
>>>>> how to figure out what it means. As far as I can tell, the code running on
>>>>> the PRU is working. I'm generating a 100Khz signal on a direct output, and
>>>>> am able to successfully measure this signal. The Beaglebone is locking up,
>>>>> though, and I believe this stack trace is being spammed so heavily that 
>>>>> the
>>>>> logging is taking over the CPU and my ssh shell gets locked out.
>>>>>
>>>>> I'm using this device tree overlay:
>>>>> https://github.com/PocketNC/BeagleBoard-DeviceTrees/blob/pocketnc-ai-test/src/arm/am5729-beagleboneai-pocketnc-pro.dts
>>>>>
>>>>> The code I'm running is implemented in PRU Assembly that is assembled
>>>>> with pasm. pasm outputs a .bin file and I need a .elf file for running it
>>>>> with remoteproc, so I'm jumping through some hoops to do that conversion.
>>>>> The elf file does seem to work, but I'm not sure if I need to do more to
>>>>> ensure I'm specifying what resources I need access to or something like
>>>>> that. I can go into more detail if need be.
>>>>>
>>>>> The stack trace is below. Any ideas about what is going on are
>>>>> appreciated!
>>>>>
>>>>> [  168.153783] ------------[ cut here ]------------
>>>>> [  168.153829] WARNING: CPU: 0 PID: 0 at drivers/bus/omap_l3_noc.c:147
>>>>> l3_interrupt_handler+0x27c/0x39c
>>>>> [  168.153851] 44000000.ocp:L3 Custom Error: MASTER PRUSS2 PRU1 TARGET
>>>>> L4_PER1_P3 (Idle): Data Access in Supervisor mode during Functional access
>>>>> [  168.153865] Modules linked in: xt_conntrack ipt_MASQUERADE
>>>>> nf_nat_masquerade_ipv4 rpmsg_rpc rpmsg_proto bnep btsdio bluetooth
>>>>> ecdh_generic brcmfmac pvrsrvkm(O) brcmutil cfg80211 uio_pruss_shmem evdev
>>>>> joydev stmpe_adc omap_remoteproc virtio_rpmsg_bus rpmsg_core 8021q garp 
>>>>> mrp
>>>>> stp llc iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat
>>>>> usb_f_acm nf_conntrack u_serial usb_f_ecm usb_f_mass_storage 
>>>>> iptable_mangle
>>>>> iptable_filter usb_f_rndis u_ether libcomposite cmemk(O) uio_pdrv_genirq
>>>>> uio spidev pruss_soc_bus pru_rproc pruss pruss_intc ip_tables x_tables
>>>>> [  168.154474] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W  O
>>>>> 4.14.108-ti-r119 #1
>>>>> [  168.154490] Hardware name: Generic DRA74X (Flattened Device Tree)
>>>>> [  168.154538] [<c0113180>] (unwind_backtrace) from [<c010d690>]
>>>>> (show_stack+0x20/0x24)
>>>>> [  168.154575] [<c010d690>] (show_stack) from [<c0ce54f4>]
>>>>> (dump_stack+0x80/0x94)
>>>>> [  168.154609] [<c0ce54f4>] (dump_stack) from [<c013f5b8>]
>>>>> (__warn+0xf8/0x110)
>>>>> [  168.154636] [<c013f5b8>] (__warn) from [<c013f628>]
>>>>> (warn_slowpath_fmt+0x58/0x74)
>>>>> [  168.154667] [<c013f628>] (warn_slowpath_fmt) from [<c0741e10>]
>>>>> (l3_interrupt_handler+0x27c/0x39c)
>>>>> [  168.154703] [<c0741e10>] (l3_interrupt_handler) from [<c01abcbc>]
>>>>> (__handle_irq_event_percpu+0xbc/0x280)
>>>>> [  168.154734] [<c01abcbc>] (__handle_irq_event_percpu) from
>>>>> [<c01abebc>] (handle_irq_event_percpu+0x3c/0x8c)
>>>>> [  168.154761] [<c01abebc>] (handle_irq_event_percpu) from
>>>>> [<c01abf54>] (handle_irq_event+0x48/0x6c)
>>>>> [  168.154792] [<c01abf54>] (handle_irq_event) from [<c01aff78>]
>>>>> (handle_fasteoi_irq+0xc8/0x17c)
>>>>> [  168.154822] [<c01aff78>] (handle_fasteoi_irq) from [<c01aad7c>]
>>>>> (generic_handle_irq+0x34/0x44)
>>>>> [  168.154850] [<c01aad7c>] (generic_handle_irq) from [<c01ab390>]
>>>>> (__handle_domain_irq+0x8c/0xfc)
>>>>> [  168.154879] [<c01ab390>] (__handle_domain_irq) from [<c01015e0>]
>>>>> (gic_handle_irq+0x4c/0x88)
>>>>> [  168.154908] [<c01015e0>] (gic_handle_irq) from [<c0d02bcc>]
>>>>> (__irq_svc+0x6c/0xa8)
>>>>> [  168.154925] Exception stack(0xc1501ed8 to 0xc1501f20)
>>>>> [  168.154946] 1ec0:
>>>>>      00000001 00000000
>>>>> [  168.154973] 1ee0: fe600000 00000000 c1500000 c1504e60 c1504dfc
>>>>> c14cbb78 c1501f48 00000000
>>>>> [  168.154997] 1f00: 00000000 c1501f34 c1501f14 c1501f28 c012fcb8
>>>>> c0109768 600f0013 ffffffff
>>>>> [  168.155031] [<c0d02bcc>] (__irq_svc) from [<c0109768>]
>>>>> (arch_cpu_idle+0x30/0x4c)
>>>>> [  168.155061] [<c0109768>] (arch_cpu_idle) from [<c0d02044>]
>>>>> (default_idle_call+0x30/0x3c)
>>>>> [  168.155092] [<c0d02044>] (default_idle_call) from [<c018cc6c>]
>>>>> (do_idle+0x180/0x214)
>>>>> [  168.155124] [<c018cc6c>] (do_idle) from [<c018d00c>]
>>>>> (cpu_startup_entry+0x28/0x2c)
>>>>> [  168.155156] [<c018d00c>] (cpu_startup_entry) from [<c0cfb4b0>]
>>>>> (rest_init+0xdc/0xe0)
>>>>> [  168.155194] [<c0cfb4b0>] (rest_init) from [<c1400eb8>]
>>>>> (start_kernel+0x434/0x45c)
>>>>> [  168.155217] ---[ end trace d9047b952a20ba7f ]---
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> For more options, visit http://beagleboard.org/discuss
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>>>>> .
>>>>>
>>>>
>>>>
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