7 ms·

Agree completely. Hard real time is possible with Linux, we use it for sub millisecond control of Traffic Lights. The only issue we ever hit is proving that the

Agree completely. Hard real time is possible with Linux, we use it for sub millisecond control of Traffic Lights. The only issue we ever hit is proving that the code running is the stuff we expected to run.

mlaretallack 8y ago
But I have to add we have a real embedded cortex checking everything, just in case ......
arcticfox 8y ago
> Agree completely. Hard real time is possible with Linux, we use it for sub millisecond control of Traffic Lights. Out of curiosity, why do traffic light controls need to be that precise?
- huehehue 8y ago
  Venturing a guess -- there's either some X% accuracy standard required by the government for who-knows-what reason, or it's for red light cameras and ticketing systems. "Ironically, the biggest concern with red-light camera systems is that they are so precise. They measure a driver’s speed and exact location within a fraction of a second — but do not leave any wiggle room for the errors of traffic signals such as inconsistent yellow light times"[0] If there's not an accuracy threshold for safety reasons, there's gotta be one when traffic ticketing revenue is on the line (also I guess determining fault at accidents, vehicular manslaughter cases, etc.) [0] https://www.mercurynews.com/2014/06/06/red-light-cameras-how-accurate-are-they/ https://www.mercurynews.com/2014/06/06/red-light-cameras-how...
- loourr 8y ago
  I don't actually know, but my guess is time drift with respect to other lights.
- jackhack 8y ago
  resume-driven development?
  - lifeisstillgood 8y ago
    everything is revenue driven development
    - jethro_tell 8y ago
      he said resume, i.e. working with tech you want to use at your next gig not the tech you need at this gig.
      - lifeisstillgood 8y ago
        could have sworn i read that right ... ah well still, revenue driven development actually makes sense as a thing too ...
coldtea 8y ago
>we use it for sub millisecond control of Traffic Lights Why would anyone need "sub millisecond control of Traffic Lights"? Traffic lights are mission critical systems, of course, but even millisecond precision should be more than enough, and possibly even 0.5x-1 second precision...
- brbrodude 8y ago
  if it controls a ton of them, then small stuff could get them to be intolerably out of sync maybe? I'm just guessing :p
- encoderer 8y ago
  The sub-millisecond precision ensures they can totally destroy your day with short left turn arrows and yellow lights.
  - xg15 8y ago
    Yes, some green phases definitely feel sub-millisecond.
- dnautics 8y ago
  For legal reasons. Regs say that stop cycles have to meet minimum times in each state, if you're even off by a Tony bit you could potentially challenge it legally in court.
- Cyph0n 8y ago
  The real question is: why do you need an entire OS kernel to control traffic lights?
  - noselasd 8y ago
    To communicate with all the other traffic lights and sensors at the other intersections on the road to optimize traffic flow.
    - 8y ago
samstave 8y ago
On a tangent, but still germane to the thread: Why arent their efforts to create "autonomous only" traffic managment scenarios, where people drive into a given, known area, and the area then takes control of managing the traffic and vehicles. Such that you relinquish control of the vehicle to that area's control system, with your destination stated and then your vehicle is managed accordingly. For example, a parking lot for a really large venue with an autonomous valet system. YOu drive up and get out and then the system takes over your car and drives off iwth it and parks it and you recall it when needed... Or managing traffic in a very heavily trafficed bottle-neck of a grid; such as the baybridge merging egress from SF financial district. If you put in your destination, and join the group, all the cars could then be managed for getting onto the bridge more rapidiously ... Autonomous doesnt need to drive me from SF to LA, but it would be great if an autonomous hive mind could get all the cars to up throughput in given situations, no?
- forapurpose 8y ago
  That seems to match the right tool (AI driving) to the right job (well-defined, well-controlled situations). I seem to recall that similar ideas go back to the early 1990s, at least, for highways: Drive your car to the entrance ramp, plug in your destination, and the autonomous system takes it from there. But for many of these things, such as the Bay Bridge or a highway, it seems like there is a simpler solution: Put the cars on a train and take them across by rail. I suspect I'm not the first person to think of it so I wonder why it's never been done (i.e., what problem I'm overlooking).
  - samstave 8y ago
    Ive been picturing the rail problem for some time as well. Not just for cars, but also for cargo... just have a constant gondola-like conveyer that detaches a platform from the line to slow it enough to allow for cargo to get on, then re-zip-it backinto the line and speed it along, de-rail it once it hits its exit/location... ideally though, in cities, there would be no surface streets and all cars would have their own level below that of bikes pedestrians. What would SF look like if a superstructure was built above all streets and all pedestrian and bike traffic was moved up there? (sure, SF may be a poor example, so just select [city]) Look at Singapore's vast underground connecting malls between facilities. Those are pretty amazing. I grade US urban/city planners rather poorly.
atomicthumbs 8y ago
So what sort of interlocks do you have on top of that to prevent simultaneous greens?
- amanaplanacanal 8y ago
  Traffic signals have hardware interlocks so that can never happen. I don't know if they are using mechanical relays or what, but you can't turn both sides green in software.

mlaretallack 8y ago

But I have to add we have a real embedded cortex checking everything, just in case ......

arcticfox 8y ago

> Agree completely. Hard real time is possible with Linux, we use it for sub millisecond control of Traffic Lights. Out of curiosity, why do traffic light controls need to be that precise?

huehehue 8y ago
Venturing a guess -- there's either some X% accuracy standard required by the government for who-knows-what reason, or it's for red light cameras and ticketing systems. "Ironically, the biggest concern with red-light camera systems is that they are so precise. They measure a driver’s speed and exact location within a fraction of a second — but do not leave any wiggle room for the errors of traffic signals such as inconsistent yellow light times"[0] If there's not an accuracy threshold for safety reasons, there's gotta be one when traffic ticketing revenue is on the line (also I guess determining fault at accidents, vehicular manslaughter cases, etc.) [0] https://www.mercurynews.com/2014/06/06/red-light-cameras-how-accurate-are-they/ https://www.mercurynews.com/2014/06/06/red-light-cameras-how...
loourr 8y ago
I don't actually know, but my guess is time drift with respect to other lights.
jackhack 8y ago
resume-driven development?
- lifeisstillgood 8y ago
  everything is revenue driven development
  - jethro_tell 8y ago
    he said resume, i.e. working with tech you want to use at your next gig not the tech you need at this gig.
    - lifeisstillgood 8y ago
      could have sworn i read that right ... ah well still, revenue driven development actually makes sense as a thing too ...

coldtea 8y ago

>we use it for sub millisecond control of Traffic Lights Why would anyone need "sub millisecond control of Traffic Lights"? Traffic lights are mission critical systems, of course, but even millisecond precision should be more than enough, and possibly even 0.5x-1 second precision...

brbrodude 8y ago
if it controls a ton of them, then small stuff could get them to be intolerably out of sync maybe? I'm just guessing :p
encoderer 8y ago
The sub-millisecond precision ensures they can totally destroy your day with short left turn arrows and yellow lights.
- xg15 8y ago
  Yes, some green phases definitely feel sub-millisecond.
dnautics 8y ago
For legal reasons. Regs say that stop cycles have to meet minimum times in each state, if you're even off by a Tony bit you could potentially challenge it legally in court.
Cyph0n 8y ago
The real question is: why do you need an entire OS kernel to control traffic lights?
- noselasd 8y ago
  To communicate with all the other traffic lights and sensors at the other intersections on the road to optimize traffic flow.
  - 8y ago

samstave 8y ago

On a tangent, but still germane to the thread: Why arent their efforts to create "autonomous only" traffic managment scenarios, where people drive into a given, known area, and the area then takes control of managing the traffic and vehicles. Such that you relinquish control of the vehicle to that area's control system, with your destination stated and then your vehicle is managed accordingly. For example, a parking lot for a really large venue with an autonomous valet system. YOu drive up and get out and then the system takes over your car and drives off iwth it and parks it and you recall it when needed... Or managing traffic in a very heavily trafficed bottle-neck of a grid; such as the baybridge merging egress from SF financial district. If you put in your destination, and join the group, all the cars could then be managed for getting onto the bridge more rapidiously ... Autonomous doesnt need to drive me from SF to LA, but it would be great if an autonomous hive mind could get all the cars to up throughput in given situations, no?

forapurpose 8y ago
That seems to match the right tool (AI driving) to the right job (well-defined, well-controlled situations). I seem to recall that similar ideas go back to the early 1990s, at least, for highways: Drive your car to the entrance ramp, plug in your destination, and the autonomous system takes it from there. But for many of these things, such as the Bay Bridge or a highway, it seems like there is a simpler solution: Put the cars on a train and take them across by rail. I suspect I'm not the first person to think of it so I wonder why it's never been done (i.e., what problem I'm overlooking).
- samstave 8y ago
  Ive been picturing the rail problem for some time as well. Not just for cars, but also for cargo... just have a constant gondola-like conveyer that detaches a platform from the line to slow it enough to allow for cargo to get on, then re-zip-it backinto the line and speed it along, de-rail it once it hits its exit/location... ideally though, in cities, there would be no surface streets and all cars would have their own level below that of bikes pedestrians. What would SF look like if a superstructure was built above all streets and all pedestrian and bike traffic was moved up there? (sure, SF may be a poor example, so just select [city]) Look at Singapore's vast underground connecting malls between facilities. Those are pretty amazing. I grade US urban/city planners rather poorly.

atomicthumbs 8y ago

So what sort of interlocks do you have on top of that to prevent simultaneous greens?

amanaplanacanal 8y ago
Traffic signals have hardware interlocks so that can never happen. I don't know if they are using mechanical relays or what, but you can't turn both sides green in software.