monkbroc · HackerTrans

monkbroc

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Gh-nag: Never forget a PR or issue again

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2 pointsby monkbroc10 tahun yang lalu0 comments

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7 tahun yang laludiscuss

Is there any reason to believe the ride sharing companies won't reorganize their drivers using a similar model to what Amazon uses for their delivery drivers: contract to external firms that employ drivers so the parent entity is absolved of responsibility?

https://www.nytimes.com/2019/09/05/us/amazon-delivery-driver...

8 tahun yang laludiscuss

Clubhouse has been a good balance of structure and simplicity. They have a good API for automation too.

https://clubhouse.io

8 tahun yang laludiscuss

Moving Day is an example of something I thought was normal but only realized was a local custom when I moved to another country.

Frozen thinly-sliced fondue meat (beef, pork, turkey) being available at any grocery store was another one. Fondue in a pot of beef broth is a popular dish for dinner parties in Québec since it scales no matter how many guests you have and each guest can eat however much or little they want. In the US the closest I can find is beef bulgogi from a Korean grocery store.

What are some examples of things you thought were "normal" until you moved elsewhere?

9 tahun yang laludiscuss

I have used ASCET, another model-based design tool. It exports the models as XML and has a separate executable that diffs the XML and renders the diagram with red outlines around the changes so you can click down into the details of the changes.

9 tahun yang laludiscuss

"Located or willing to relocate" is in Preferences, but yeah we should make it clearer in the listing that it's a nice to have.

9 tahun yang laludiscuss

Particle | Site Reliability Engineer (SRE), Front-end Engineer | San Francisco, Minneapolis or worldwide REMOTE | www.particle.io

Particle is the largest developer community in the Internet of Things (IoT) with over 120,000 engineers and hundreds of companies building products on our platform. If you've used our Photon dev kit for one of your projects at home, you know why!

We're looking for people to join our worldwide engineering team to scale our backend systems and to build the tools used by Particle customers. If you have a passion for user experience, have a bias towards shipping and believe that tests are the key to higher velocity and reliability, you'll fit right in.

Our stack is mostly JavaScript, with some Ruby and Go, dockerized and deployed on AWS. The secret sauce is in the distributed systems that allow IoT devices to talk in real-time with customer applications. Come talk to us if you want to know more!

Apply directly to https://particle.io/jobs

10 tahun yang laludiscuss

Also try "what the hat". Heard it from my 5 y.o. son.

10 tahun yang laludiscuss

8/40

I heard the story of the Exeter research on NPR while driving back from the airport at night last year at it floored me! I never realized that other people could actually picture images in their minds. I also thought this was entirely metaphorical. I wrote to the researchers back then to be included in further research.

I'm a computer engineer.

Anyone know if there a community group of people with aphantasia?

10 tahun yang laludiscuss

Google Photos is still missing a lot of functionality of Picasa. For year I've been uploading pictures to an album named with the current year. My parents and in-laws can check the pictures of the kids when they like. The Photos upload activity on Android doesn't have a selector for the album like the Picasa upload did.

There still doesn't seem to be a way to interact with Google Photos through scripts. Search for "google photos api" and the first link is still the Picasa Web Albums Data API...

11 tahun yang laludiscuss

Did you end up changing your routine or did you stick to it? I started stronglifts 5x5 a few months ago and the weights are heavy enough now that I'm failing sets in most exercises each session. It's hard to get the motivation to keep going.

11 tahun yang laludiscuss

The Michigan Department of Environmental Quality instructed Flint residents to flush their tap for 2 minutes before sampling the water which under-represented the amount of lead in the water. The EPA doesn't explicitly forbid flushing but doesn't recommend it.

http://flintwaterstudy.org/

11 tahun yang laludiscuss

The "closed by default" attitude drove me nuts. Teams develop tools to improve their work and refuse to share the source code, even internally, even when there is a business reason (I'll improve the tool for you and me). Forget about cross-company collaboration on open source like you see in web dev.

11 tahun yang laludiscuss

All good points.

The CPU, Flash and RAM share the silicon die with lots of specialized peripherals like CAN controllers and hardware timer units. There's a lot more on the chip than just a CPU.

Also, cost is king in automotive...

11 tahun yang laludiscuss

Without going into specifics, there was a static analysis tool that was part of the toolchain that caught multiple writes in different modules or in tasks of different priorities. It was a build error unless allowed on a case-by-case basis.

11 tahun yang laludiscuss

You're welcome.

There is only one OS task for each rate (10ms, 100ms, etc). The order of the function calls in each task is determined at compile time while respecting constraints (A_10ms must run before B_10ms because B_10ms uses values computed in A_10ms).

In addition each OS task has an overrun monitor that triggers if a task is scheduled to run but the previous run has not finished yet. This type of error typically sets a "control module performance" diagnostic trouble code.

11 tahun yang laludiscuss

Background: I used to be an automotive software engineer. I speak for myself only here.

Whenever the topic of automotive software comes up on HN there are comments alongs the lines of "global variables bad", but not much construtive feedback.

I want to explain some of the tradeoffs that lead to the architecture used in automotive software to get a better discussion going with HN readers about that architecture.

tl;dr Given the hardware restrictions, real-time requirements and measurement capabilities required in automotive software, shared global variables without locks is a fast and safe way to share state between different software components as long as each variable is only written in one place in the program.

The microprocessor has to run for 10+ years in a wide range of temperatures and be dirt cheap, so you end up with specs like 180 MHz, 4 MB of flash and 128 KB of RAM.

The program must run deterministicly with respect to memory. There is no malloc/new in the code. All variables are statically allocated.

Because the physical world doesn't pause, no code is allowed to block while waiting for resources, especially synchronization primitives like mutexes.

The software architecture is in 2 main parts: basic software containing the real-time OS and hardware drivers, and the application layer which has the domain-specific code for controlling the engine, brakes, etc.

The basic software is implemented using usual C programming techniques. It has an API provided by function calls and structs to hide implementation details of each microcontroller.

The application software is where the programming model is different.

To understand why, you need to know where automotive software comes from and what it is trying to acheive.

Originally all controllers were mechanical: a valve opens proportionally to the vacuum in a part of the system. Then some controllers were implemented in analog electronics: take multiple voltages, feed them through an op-amp and use the output to control a valve.

So automotive software reproduces this: get some inputs, compute the same physical equations at a regular rate and generate outputs.

This is dataflow programming. Blocks of code have inputs and outputs. They are executed at a fixed rate that depends on the physical phenomena (air flow changes fast, temperature changes slowly). Different blocks are conneceted together in a hierachical way to form subsystems. Encapsulation is acheived by viewing these blocks as black boxes: you don't need to care how the block works if you are only interested in knowing which inputs it uses and outputs it produces.

Here's an example component to control a gizmo.

It might be implemented in a visual environment like Simulink by MathWorks, or it implemented by hand from a spec.

  #include "GizmoController_data.h"
  
  void GizmoController_100ms() {
    Gizmo_Gain = interpolate2d(Gizmo_Gain_MAP, EngineSpeed, CoolantTemp);
  }
  
  void GizmoController_10ms() {
    Gizmo_Error = Gizmo_PositionDesired - Gizmo_Position;
    Gizmo_DutyCycle = limit(Gizmo_Gain * Gizmo_Error + Gizmo_Offset_VAL, 0, 100);
  }

It takes some inputs (EngineSpeed, CoolantTemp, Gizmo_PositionDesired, Gizmo_Position), has some intermediate values (Gizmo_Error), and outputs (Gizmo_DutyCycle). Those are implemented as global variables. It also uses some constants (Gizmo_Gain_MAP, Gizmo_Offset_VAL). It has 2 processes, running every 100ms and 10ms. All this information would be specified in an XML file.

The header GizmoController_data.h is auto-generated at compile time by a tool from the XML file mentioned above. It will contain global variable definitions for the inputs, intermediates and outputs with the appropriate volatile, const, static and extern storage classes/type qualifiers. This ensures that the compiler will enforce that inputs can't be written to, intermediate values are private to the component and outputs can be read by other modules.

Note that no explicit synchronization is needed to access inter-process variables like Gizmo_Gain or inter-component variables like Gizmo_Position. It's shared memory between 2 processes scheduled in OS tasks that can potentially interrupt each other, but since the write is atomic and happens only in one place, there is no data race. This is huge! Concurrent programming, without locks, with the best efficiency possible, using a simple technique anybody can understand: only one place in the program is allowed to write to any global memory location.

Calibration is another aspect of automotive software. In most software the constants either never change or can be set in some kind of configuration file. For an automotive controller, the value of constants (gains, offsets, limits, etc) depend on the vehicle so they must be configurable at run time during development. This is implemented in the C code by putting all constants in a memory area that is ROM in production units, but RAM in development units. The compiler enforces that application software cannot change constants, but the basic software includes code so that constants can be changed from the outside in development. This process is called calibration and is done by calibration engineers who are usually not the ones who wrote the software. Note that calibration can drastically affect the behavior of the software. What would happen if Gizmo_Gain_MAP is set to all zeros?

Measurement of variables is essential to understanding what's going on inside the embedded controller. Having all that state available in global variables makes it possible for the calibration tool request the value of any variable in the software at a fixed rate and display it in a virtual oscilloscope.

The measurement and calibration tool needs to know how to access the variables and constants. It uses a file that maps from names to addresses for a particular version of software. That file can easily be generated a compile time since all allocations are static.

Going back to the architecture of the application software, let's look at where our gizmo controller fits. It is not the only component needed to make the gizmo work. You also need components to calculate the gizmo position from some external signal (let's say an analog voltage), to route the output signal to the powerstage driver on the PCB, to determine which position the gizmo should currently occupy. These would form the gizmo subsystem package.

When the supplier releases gizmo 2.0 (TM) they upgrade the input signal to be a PWM input instead of an analog input. Modularity in the software allows the software team to simply replace the gizmo position component with one that reads a PWM instead of an analog voltage and keep the rest of the gizmo subsystem the same. In the future, projects that use gizmo 1.0 use one version of the gizmo subsystem and projects that use 2.0 use another.

This is true at any level in the hierarchy: as long as the inputs and outputs are the same, a component or subystem package can be replaced by another.

Version control in automotive software reflects this. Instead of having one tree of versions and releases like a typical software project, each component, subsystem package and software project has its own tree of versions. Each software project will reference the subsystem packages required for their engine type, vehicle platform, sensors and actuators, etc. This is how code reuse is acheived.

Testing is a mix of simulation (the sensor/actuator is simulated in Simulink and connected to Simulink block diagram of the software component), hardware-in-the-loop (a computer simulates the vehicle, but the real electronic control unit is used) and vehicle testing.

Thanks for reading. I hope this improves your understanding of how automotive software is structured.

I'm hoping the discussion will bring examples from other fields like robotics, drones and aeronautics that have similar real-time requirements on how they architect their software.

11 tahun yang laludiscuss

VW does not own most of the software running in their cars. Most software is IP of their many suppliers. Those suppliers sell the same software to many car manufacturers so to say they would oppose giving their source code to VW so it could release it to the public is an understatement.