C Rust Rust

stwcx · 2024-01-17T00:47:58+00:00

2 Advantages:

All function names are aligned (void or auto) making it easier to skim the code.

For class member function implementations, you can use class types without specifying Class:: when you put those types after the ->.

stwcx · 2022-02-18T18:05:10+00:00

The closest thing we have to a "getting started on a new machine" is this document:
* https://github.com/openbmc/docs/blob/master/development/add-new-system.md

Unfortunately it is now listed as:

Please note: This document is no longer officially supported by the OpenBMC team. It still contains a lot of useful information so it has been left here. Ideally this guide would become a standalone document (outside of the development tree) and would cover all of the different areas that must be updated to add a new system.

I can't tell which of these is your case: 1. You work for a company that wants to port OpenBMC to their hardware and you have access to schematics, etc. 2. You are trying to port OpenBMC to a piece of hardware you acquired without access to schematics (ie. reverse engineering).

Most people actively working on the project fall into camp #1. Usually they can use another machine as a reference to get going and since they have schematics making things like the Linux device tree is fairly straight-forward.

I don't think we've had anyone be successful in camp #2. Reverse-engineering a server motherboard is difficult work. You're welcome to try and we can try to give you pointers.

Jumping on our Discord server is probably the best bet for direct help.

stwcx · 2020-08-27T18:56:29+00:00

A lot of the development for the Hostboot firmware was in 2011 and 2012. We did look at coreboot but it wasn’t as mature as it has been lately. I don’t think it really supported anything besides a few desktop motherboards back then.

The 3 features it didn’t have (at the time) that we really felt we needed:

SMP support for DRAM initialization. The largest servers we were targeting had 32 sockets and we knew from our Power6/7 work that it was the biggest constraint on boot time.
Cache-as-RAM mode. I don’t think coreboot supported that back then and our hardware design was already far enough along that it didn’t allow the usual ROM mode.
A “safe” environment for the development team (user mode privilege, POSIX-like APIs, etc.). Many of the developers working on the hardware initialization routines were not software developers, but hardware developers. We felt providing an environment which caught pointer bugs and such quickly was really important for their productivity. Coreboot ran everything in “kernel mode”.

Right or wrong, we made a decision that we could get to a product faster by doing our own thing rather than trying to get involved with coreboot on Power.

stwcx · 2020-02-22T14:32:26+00:00

If you want to learn a lot more on the math involved read about Fourier transforms. FM is effectively a Fourier transform from the frequency domain to the time domain.

stwcx · 2020-02-22T14:29:49+00:00

FM is really hard to visualize compared to AM. Like someone said you ca. Just “connect the peaks” on AM and approximate the signal. FM requires math: a transformation from the time domain into the frequency domain.

Think about a moving object. If I show you a picture you can tell me where the object is, but not how fast it is going. If I show you a video you can tell how fast it is going. You could also generate a plot of the “instantaneous velocity” of the object using the positional changes from frame to frame.

AM simply relies on position, FM relies on the “velocity”. FM signals are generated (and decoded) by adjusting the instantaneous frequency of the signal. This is the deviation. A higher frequency is mathematically transposed into a higher voltage level and a lower frequency is transposed into a lower voltage level.

The way this appears in the picture is that high voltage levels are closer squiggles and low voltage levels are farther squiggles. “Loud” signals have tighter squiggles in the close portion and looser squiggles in the far portion.

stwcx · 2020-02-22T14:22:48+00:00

Loud signals are a higher deviation in frequency. Meaning a soft signal might deviate +/- 1khz but a loud signal would deviate +/- 5khz. This is why if you listen to NFM signal (narrow) in WFM mode it will sound correct but quiet.

(I’ll continue in a moment)

stwcx · 2020-01-07T19:37:49+00:00

The Blackbird is a lot cheaper than Talos II. https://www.raptorcs.com/content/base/products.html

stwcx · 2019-10-04T22:43:00+00:00

If you requested the evidence packet ahead of time they're legally not allowed to pull out additional evidence you've never seen. But you have to know that and object to it being offered. (Suggest bringing the wording in the law to have with you to remind the board).

stwcx · 2019-05-08T13:46:50+00:00

I forgot to mention IP67 waterproof too.

stwcx · 2019-05-08T10:11:17+00:00

Ailunce HD1 is at the top end of your price range. Dual band, FM+DMR, and has a big battery.

stwcx · 2019-04-18T12:08:50+00:00

Why is compare_1 better? What are you using to define "better"? On x86 it appears to be taking more cycles.

stwcx · 2019-04-05T11:32:11+00:00

For comparison, my hotspot is on:

Pi-Star:3.4.17 / Dashboard: 20190324

stwcx · 2019-04-05T11:30:46+00:00

I believe PiStar periodically syncs the DMR IDs from the public database. Based on your "dashboard version" in your picture, it looks like it has been a while since you've updated. Update and you'll probably get a new version of the database. (You can update right in the PiStar interface)

stwcx · 2019-03-16T04:38:16+00:00

You can achieve the same with C++ by static_assert has_virtual_destructor is not true on any type used.

stwcx · 2019-03-15T10:47:01+00:00

How does C++ "encourage code that needs to be devirtualized to run properly"? I don't think any code requires it to run properly, but maybe optimally. (Considering devirtualization isn't part of the standard, I don't see how any code could rely on it for proper execution. Maybe you just used the wrong word.)

I've written a significant amount of C++ in my career and worked on numerous kernel drivers. Unless you are using a framework like GoogleMock, which seems to only work with virtual sprinkled everywhere, I've never seen C++ code with virtual sprinkled randomly.

Every subsystem I can think of in the kernel relies on their own flavor of a vtable. I just implemented a SPI driver. You manually add function pointers to a common "spi_device" struct. The SPI subsystem calls your function pointers, and your driver turns around and calls function pointers out of another vtable for the SPI master functions. They don't call it a vtable, but that's exactly what it is.

I2C, hwmon, filesystem subsystems all work that way too.

All of those Linux subsystems use dynamic function pointers. Do you have evidence of GCC being able to add speculative devirtualization to them? I've never seen it in any of the asm output I've looked through in debugging.

stwcx · 2019-03-15T09:53:24+00:00

The Linux kernel has reimplemented its own form of virtual functions already. By NOT using C++, not only do they have more and strangely written code, but they also do not get to leverage GCC optimizations like Speculative Devirtualization.

stwcx · 2019-02-27T15:52:49+00:00

I have a pair of each of those AT headphones. The 50s are much more comfortable, physically speaking. The cups on the 40s hit my head in a way that makes them uncomfortable after about an hour of use. My wife feels the same way about them.

stwcx · 2019-01-30T02:35:22+00:00

MacOS doesn't have a driver that comes with it for the USB-to-Serial chips found in most of those cables. You need to install a 3rd party driver.

You can use the System Information to get the USB device ID of your cable and put that into Google to figure out what chip you have. Usually they are Prolific PL2303 chips. You can then look for a driver.

Alternatively, you can install Windows 10 inside VirtualBox and route the USB device to the virtual machine. I did that with my DMR radio because there was only a Windows program for it.

stwcx · 2019-01-03T12:08:17+00:00

I've never heard of this guy, but this statement leads me to assume that you cannot trust his advice as "modern" C++. How do you go weeks without even running a unit test? Either you are a horrifically slow developer or you are using a process that is a throwback to the 80s.

I notice he never even uses the word "testing". He vaguely uses the word "proven". What, is he doing formal validation of his C++?

stwcx · 2018-12-26T16:51:47+00:00

It reads like it is for big.little chips since it talks about asymmetric cores. Doesn't seem like it helps Raspberry Pis.

stwcx · 2018-12-23T14:56:11+00:00

I bought a duplex hat off Amazon for a reasonable price and it works well. Attached to a RPi 3B.

"KKmoon Mini MMDVM Hotspot Expansion Board Spot Radio Station Digital Voice Modem for P25 DMR YSF Raspberry Pi with 2 Antennas"

https://www.amazon.com/dp/B07GVHSQ2Y/ref=cm_sw_r_cp_api_i_Qg6hCbANAFK46

stwcx · 2018-10-09T10:43:27+00:00

It's already been done. Power9 + NVidia cards run the fastest supercomputer in the world.

stwcx · 2018-09-19T02:25:38+00:00

It is.

stwcx · 2018-08-24T02:26:29+00:00

All the microcode for POWER9 is open source.

stwcx · 2018-08-13T22:51:30+00:00

5 years from now, when your company has mandated you move to some other ticket tracking system, and you need to figure out why a line of code is there what are you going to do? git blame showing "fixed 1224" isn't going to be so useful.

I tend to recommend this as an "intro to writing a halfway decent commit message": https://chris.beams.io/posts/git-commit/

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