On Tue, Feb 9, 2021 at 5:55 PM Michael Wong <fraggamuffin@gmail.com> wrote:

Topic: SG14 Low Latency Monthly
This meeting is focused on Embedded. It will be chaired by John MacFarlane.
Hi,
Michael Wong is inviting you to a scheduled Zoom meeting.
Topic: SG14 monthly Dec 2020-Feb 2021
Time: Jan 13, 2020 02:00 PM Eastern Time (US and Canada)
    Every month on the Second Wed, until Feb 10, 2021, 3 occurrence(s)
    Dec 9, 2020 02:00 PM
    Jan 13, 2021 02:00 PM
    Feb 10, 2021 02:00 PM
    Please download and import the following iCalendar (.ics) files to your
calendar system.
    Monthly:
https://iso.zoom.us/meeting/tJcscuigqD8pHNESxi1bJ9ClURVqr_ZAvmv1/ics?icsToken=98tyKuCrrz4rEtKRsx-CRowqBY_4d_zwpilego14rwfsUiJ5OyD6A9B0I6BAKvnG
Join from PC, Mac, Linux, iOS or Android:
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Agenda:
1. Opening and introduction
ISO Code of Conduct
<
https://isotc.iso.org/livelink/livelink?func=ll&objId=20882226&objAction=Open&nexturl=%2Flivelink%2Flivelink%3Ffunc%3Dll%26objId%3D20158641%26objAction%3Dbrowse%26viewType%3D1
>
ISO patent policy.
https://isotc.iso.org/livelink/livelink/fetch/2000/2122/3770791/Common_Policy.htm?nodeid=6344764&vernum=-2
WG21 Code of COnduct:
https://isocpp.org/std/standing-documents/sd-4-wg21-practices-and-procedures
1.1 Roll call of participants
1.2 Adopt agenda
1.3 Approve minutes from previous meeting, and approve publishing
previously approved minutes to ISOCPP.org
1.4 Action items from previous meetings
2. Main issues (125 min)
2.1 General logistics
Future meeting plans
Apr 14, 2020 02:00 PM ET/1800 UTC: Finance focus on low latency
May 12, 2021 02:00 PM ET/1800UTC: Games
June 9, 2021 02:00 PM ET/1800 UTC: Embedded
2.2 Paper reviews
Compound assignment

C++ 20 deprecates compound assignment to volatile

memory map devices is common and uses this and create larger rift between C and C++ world

harder to get c project to just recompile in C++, now you have to replace compound assignment

header files also contain macros like this

its only deprecation but it is an intent to remove

difficult to pinpoint semantics problems, one read, one writeback

code that he does not control, and vendor headers in macros is the problme

the semantics of solution in paeper are the same

can we get C to deprecate this ?

most of volatile is unspecified what it means

we do a read of register and or it with something

reading a device register dont give you any sensible value back

for some HW it might work or not work

if deprecation is not good, and attach proper semantics, then write a paper

main way for a bit set

impedance mismatch of the fundamental unit of byte

hard to read |= in a data race

the scenario can exasperate it during times when no memory order

C/C++ liasion group to deprecate this in C

fix with replacing compound with non-compound, this just impose a style from C++ without benefit, so may not want to deprecate compound ops

this is a well known idiom on some embedded HW

fix in embedded world with a style guide with MISRA

changes a lot of old code prevents moving to C++ in embedded, so recommend style guide to fix this

might not be funneling people down a path at all, but using operation provided to them by HW vendor

here is a piece of code that works in C and now they want me to try C++

; now this make people move back to C

a|=b

a=a|b

volatile atomics that can give slightly better semantics in some use case, but it is implementation specific

so specific semantics=volatile is used when using HW or signal, these need specific instructions

compiler might only honor the size, and not CAS

could this be a compiler warning? could be lots of false positive, what used to be there is fine

looks annoying to have this deprecation, will be no go for C++ in our tools

what are instructions emitted by volatile access, we sue C++ on CPU side and in FPGA, and replace C++ program with equivalent, and is volatile is emitting memory access

need to keep this as it is simpler for end user

support the other which is we see so many time in our code, assume that when you write compound that you are doing RMW , was always a bug

so obviously misleading and hard t keep safeguard

what would be good outcome here, easiest is to undeprecate, but what do you say? you dont say what they do and it is implementiaton specified, valid syntax, but you dont know what it means

std should define semantics of compound operation but that might make it worst

counter argument is it also has no defined semantcis in C either, C does not warn you but C++ does, so we make it appear to have different behavior when there is no difference

define volatile? yes there is another paper that is trying to define meaning of volatile load and store, and atomic volatile

ask C/C++ liasion about deprecatign for C23, if NO then we know we have input

JF to email aaron

hard to get a good feelign about each other's interest; see no consensus from the discussion, mixed on both sides

Freestanding?

P2268R0 is a roadmap

P2013 Language optional on EWG EP

P1642 Easy utilities in LEWG EP

Low cost deterministic exception for next Embedded call

P0829 is Std lib omnibus

beyond are still being discussed and needs implementation experience

Asking for volunteers

This is a future directions paper on embedded which is more then most desktops

PB has a fork of this paper

2.2.1 any other proposal for reviews?
SG14/SG19 features/issues/defects:
https://docs.google.com/spreadsheets/d/1JnUJBO72QVURttkKr7gn0_WjP--P0vAne8JBfzbRiy0/edit#gid=0
2.3 Domain-specific discussions
2.3.1 SIG chairs
   - Embedded Programming chairs: Ben Craig, Wouter van Ooijen and Odin
   Holmes, John McFarlane
   - Financial/Trading chairs: Staffan TjernstrÃƒÂ¶m, Carl Cooke, Neal
Horlock,
   Mateusz Pusz, Clay Trychta,
   - Games chairs: Rene Riviera, Guy Davidson and Paul Hampson
   - Linear Algebra chairs: Bob Steagall, Mark Hoemmen, Guy Davidson
2.4 Other Papers and proposals
2.5 Future F2F meetings:
2.6 future C++ Standard meetings:
https://isocpp.org/std/meetings-and-participation/upcoming-meetings
-
3. Any other business
Reflector
https://lists.isocpp.org/mailman/listinfo.cgi/sg14
As well as look through papers marked "SG14" in recent standards committee
paper mailings:
http://open-std.org/jtc1/sc22/wg21/docs/papers/2015/
http://open-std.org/jtc1/sc22/wg21/docs/papers/2016/
Code and proposal Staging area
https://github.com/WG21-SG14/SG14
4. Review
4.1 Review and approve resolutions and issues [e.g., changes to SG's
working draft]
4.2 Review action items (5 min)
5. Closing process
5.1 Establish next agenda
5.2 Future meeting
April 14, 2021 02:00 PM Eastern Time ( 1800 UTC ): Finance

Kind Rgds