Reminder: Zephyr Project: APIs

When: Tuesday, 24 March 2020, 9:00am to 10:00am, (GMT-07:00) America/Los Angeles

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Hello,

On Tue, 24 Mar 2020 11:25:48 +0200
"Jukka Rissanen" <jukka.rissanen@...> wrote:

Hi Darryl,

I think it is more of a historical relic than a purpose design. There
has not been any reports that this have caused issues. Patches are
welcome of course.

Perhaps it could be rephrased differently: net_buf is more like Zephyr's
internal system object. Where it's used currently, thread
synchronization is expected(*) to happen on different level(s), and
net_buf itself is kept lightweight and optimized. Perhaps that can be
changed, but effects on existing subsystems using net_buf should be
considered.

(*) That doesn't mean there're no bugs, so reproducible bugreports are
welcome.

Cheers,
Jukka


On Sun, 2020-03-22 at 17:39 -0700, Darryl Gamroth wrote:

Hi all,

I was looking at using net_bufs for an application broadcasting
reference counted buffers to multiple threads and I noticed the
reference counting is not atomic. I'm curious, is this by design?

Thanks.

--
Best Regards,
Paul

Linaro.org | Open source software for ARM SoCs
Follow Linaro: http://www.facebook.com/pages/Linaro
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Hi all,

Note: This is the last week where the meeting takes place at 17h CET. Next week we go back to 18h CET.

Today's topics:

- How to document standalone drivers like the enc28j60 (Piotr)

- Upgrade the hwinfo API to stable
- PR: https://github.com/zephyrproject-rtos/zephyr/pull/23661

- RTC API proposal
- PR: https://github.com/zephyrproject-rtos/zephyr/pull/23526/commits/2880ee02b0f2fd91d897d8a11a4cbdefe87a19b0

- Naming in the async_notify module
- PR: https://github.com/zephyrproject-rtos/zephyr/pull/23601

Additional items in the "Triage" column in the GitHub project may be discussed if time permits.
If you want an item included in the meeting, please add it to the GitHub project.

https://github.com/zephyrproject-rtos/zephyr/wiki/Zephyr-Committee-and-Working-Group-Meetings#zephyr-api-discussion
https://github.com/zephyrproject-rtos/zephyr/projects/18
https://docs.google.com/document/d/1lv-8B5QE2m4FjBcvfqAXFIgQfW5oz6306zJ7GIZIWCk/edit

Regards,

Carles

Hi Darryl,

I think it is more of a historical relic than a purpose design. There
has not been any reports that this have caused issues. Patches are
welcome of course.

Cheers,
Jukka

Hi,

Iam using nrf52840 development board, developing software using zephyr.
In software development iam using bluetooth as a peripheral and uart in interrupt mode(to get data from other module), when iam trying to run both interfaces the getting below errors and iam included watchdog timer so after sometime it is restarting.

Hi all,

I was looking at using net_bufs for an application broadcasting reference counted buffers to multiple threads and I noticed the reference counting is not atomic. I'm curious, is this by design?

Thanks.

Dear all,

This email is a request to change the stability of the Hardware Information API from "unstable" to "stable".

Pull-request: #23661
Discussion in the API meeting takes place on Tuesday, March 24th.

If there are any objections, please comment on the PR or attend to the API meeting.

Kind regards,

--
Alexander Wachter

The guy who introduced this API

Reminder: Zephyr Project: Dev Meeting

When: Thursday, 19 March 2020, 8:00am to 9:00am, (GMT-07:00) America/Los Angeles

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Zephyr Toolchain Working Group

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Reminder: Zephyr Toolchain Working Group

When: Thursday, 19 March 2020, 7:00am to 8:00am, (GMT-07:00) America/Los Angeles

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Description: Zephyr Working Group is inviting you to a scheduled Zoom meeting.

 

Topic:  Zephyr Toolchain Working Group

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Hi,

Thanks for clarification.

Ravi

Hello,

On Wed, 18 Mar 2020 11:34:00 +0200
"Ravi kumar Veeramally" <ravikumar.veeramally@...> wrote:

Hi,

what should be the return value or behavior of socket poll() call in
case of TCP socket is closed from peer side.

If a peer closes TCP connection from its side, it's effectively an
analog of EOF condition. In this case, poll() should return POLLIN.
This will cause a client to issue a recv()/read() call, which will
return 0, and will let a client detect the EOF condition.

This is one of the "most basic" of "not immediately obvious" API
contracts re: sockets and polling. It's definitely something like that,
because quickly looking for normative references in the POSIX standard,
I can't find them, e.g. in
https://pubs.opengroup.org/onlinepubs/9699919799/functions/poll.html
this particular case isn't described (some other "not immediately
obvious" cases are). So, it's a kind of common knowledge, and a lot of
software relies on that behavior (well, it's not possible to write
async socket code without it). If you google for it, you should be able
to find a lot of references.

Note that there's also a POLLHUP flag, behavior of which in regard to
sockets is "less clear" and "somewhat of a gray area".

As per
https://github.com/zephyrproject-rtos/zephyr/blob/master/subsys/net/lib/sockets/sockets.c#L1018,
zsock_poll_prepare_ctx() call returns -EALREADY.

zsock_poll_prepare_ctx() is an internal function, which uses a special
internal API contract, where particular error codes are used to signal
very specific conditions. -EALREADY is one of such codes. It doesn't
reach public API clients (and doesn't have the same meaning as POSIX
EALREADY error).

But
https://github.com/zephyrproject-rtos/zephyr/blob/master/subsys/net/lib/sockets/sockets.c#L1088.
Return value of z_fdtable_call_ioctl() function call handler assumes
"If POLL_PREPARE returned with EALREADY, it means it already detected
that some socket is ready."

Right, to achieve the behavior described above.

I did a simple test with few modifications in echo-client and
echo-server in net tools. echo-server closes the client connection.
poll(fds, nfds, 0) call returns "> 0" and error value set to 0. But
send failed with return value -ve and error value set to ESHUTDOWN.

That sounds *about* right. Except that POSIX requires EPIPE to be
returned trying to write to a socket with underlying connection closed.
Or to be more exact, with the quote
(https://pubs.opengroup.org/onlinepubs/9699919799/functions/send.html):

-------
[EPIPE]
The socket is shut down for writing, or the socket is
connection-mode and is no longer connected. In the latter case, and if
the socket is of type SOCK_STREAM or SOCK_SEQPACKET and the
MSG_NOSIGNAL flag is not set, the SIGPIPE signal is generated to the
calling thread.
-------

So, if we return ESHUTDOWN, we should change that to EPIPE.


If your mail trails to the ultimate question of "how to detect
peer-closed socket if we called poll with POLLOUT?", then to keep it
short:

a) Hmm, I don't have an answer right away, though I bet I used to
consider it (likely outside Zephyr context).
b) I bet that's where POLLHUP return status kicks in.
c) In all cases like that, where we can't "extract" normative behavior
description from POSIX, we should check and follow the behavior of a
well-know implementation, and that's definitely Linux.

Any thoughts @rlubos <https://github.com/rlubos> @pfalcon
<https://github.com/pfalcon>?

Please don't hesitate to cc: me on mails like this, I may sometimes not
check the mailing list for a few days.

Regards,

Ravi.

[]

--
Best Regards,
Paul

Linaro.org | Open source software for ARM SoCs
Follow Linaro: http://www.facebook.com/pages/Linaro
http://twitter.com/#!/linaroorg - http://www.linaro.org/linaro-blog

Hey everyone,

here's another update regarding the ARMv7 port: other than the 'interrupt' test, which I blacklisted, I've now got green lights on all kernel tests running on the QEMU Cortex-A9 (Zynq) target which are not automatically de-selected for whatever reason (61 passed, 23 skipped, 10 discarded). As a solution for the 'interrupt' test assertion failure is already being discussed and as I moved over completely to Stephanos' GIC interrupt handling code (although my code base isn't at the most recent regarding the modification of the interrupt handling, I'll take care of that soon), any solution of this issue should reflect directly in the ARMv7-A branch, eventually making the blacklisting obsolete.

There's been one major change along the way: I've exchanged the timer being used to drive the system. As some of the tests that failed were related to the tickless mode, and as the readily available Xilinx TTC driver isn't suitable for this mode (it's a self-reloading 16-bit counter, where dynamically calculated comparator values would require on-the-fly re-calculation of a prescaler, which would lead to varying imprecision in timing, and where, for example, you might miss out on an entire interval if interrupts are globally locked for more than one period), I've switched over to the ARM global timer, for which Carlo has already provided a high-level interface plus an access implementation in aarch64. The ARM global timer is similar to the timers that drive the system clock on the other architectures, continuously counting up while comparing against an absolute value. While on ARMv8 access is possible via special instructions, on ARMv7 the timer's identical register layout is memory-mapped. So I've added a register-based implementation in aarch32, for which the timer's device tree entry must be supplied with an additional base address. Using this timer, the tickless mode tests passed as well. The fact that the tests failed with the TTC driver might eventually be a test suite issue - the TTC driver doesn't set the tickless capability config flag when it is chosen in the build configuration, yet the test cases didn't get filtered out?

There's just one catch: I had to extend the ARM global timer's interface a little in the aarch32 implementation. While Carlo's implementation provides the basic functions for reading the current value and writing to the comparator which I re-implemented for aarch32, I had to add functions that read and write the state of the interrupt status ("event") bit. Initially I observed that the timer's ISR always ran twice in a row (the IAR register returns the timer's vector twice in a row before returning 0x3FF) when not using the auto-reload feature in tick-based mode (when configured this way, the interrupt works just as expected), erroneously incrementing the comparator value and leading to some really wonky timing behaviour.  I spent the best part of a day experimenting with various things such as extra barriers, puzzled why these double interrupts kept occurring. Eventually, I came across both ARM's and Xilinx's errata documentation - lo and behold, this behaviour is an actual bug in the MPcore silicon (which QEMU even emulates!). The suggested workaround is to clear the event bit *after* updating the comparator (to UINT64_MAX in tickless mode, some value must always be written from within the ISR) and checking its value whenever the ISR is entered. During the second, erroneous execution of the ISR, polling the event bit's value returns 0 as the comparator hasn't matched yet and the ISR exits upon detecting that no event is pending. This is also how the Linux folks implemented the workaround in their driver. It doesn't prevent the extra ISR execution, but at least it doesn't screw up the system's timing. Carlo, would you mind if I added a menuconfig option below the ARM global timer in order to enable the (ARMv7-specific) workaround and included the special handling #ifdef'd in arm_arch_timer.c -> arm_arch_timer_compare_isr()? Also, do you see any use in adding an option enabling the auto-update of the comparator in tick-based mode? It doesn't improve the interrupt latency in any way, it would just save two register writes in my case. I guess it's not that relevant, what do you think?

The one thing that works but isn't yet as clean as I would like it to be (and which should also have a matching test case for aarch32) is the FPU register saving thing. So far, I've completely skipped the CONFIG_FP_SHARING setting whereever I've added a branch for ARMv7 - if it's an ARMv7-A and if it has a FPU, pull the register saving off. Yet, while there is no marker which single thread gets to use the non-shared FPU registers as there is on Cortex-M, and the register saving basically isn't optional once the FPU is in play, I should probably auto-incorporate the FP_SHARING flag just to keep the semantics clean. I also still have to add the setting of the initial FPSCR and FPEXC values to the arch-specific thread creation code. More on that in the next update, I guess...

I'll have a look into how pull requests work and start off small with the minor bugfixes in the existing UART/TTC drivers, while with regards to the rest of my work I still have to work out with the big wigs at work if I personally get to take the credit in the copyright notices of any new sources, or if they'll mention the company - after all, they provided the resources.

Best regards,
Immo

Thanks, It's fixed