This is a discussion for the 1MB flash limit issue so that we can consolidate any discussions and concerns about it in one place.
To give some background, all Pixhawk (and compatible) boards use STMicroelectronics's STM32F427 as their main CPU. This CPU is advertised as having 2MB of flash space (flash is where the ardupilot software is held) but we have discovered that early revisions of this CPU (RevA, RevY and Rev1) have a hardware problem and can actually only hold 1MB and if we use more than that they start exhibiting USB communication problems.
Now currently APM:Copter-3.4 is 0.9MB so it's under the limit but as we add new features it grows and if it grows above 1MB users will find they can't reliable connect the ground station to the board using a USB cable (wireless would still work) which could make it very difficult to configure the board, download logs, etc.
We think many boards (perhaps most boards) out there are the early revisions (A, Y or 1) which suffer from this problem. All the boards on my desk have this problem and you can check your board by following the instruction also shown in the video:
- Ensure your Pixhawk (or compatible) is loaded with a recent version of ardupilot (like APM:Copter-3.3.x)
- Connect with the Mission Planner
- Go to the Terminal screen and select "NSH" on the drop-down on the left, then push the little green connect button beside the drop-down
- type "ver all" and press Enter quickly into the terminal (the "Overtime in task 19" causes the MP some troubles)
- look for the "WARNING! Revision Y has a silicon errata".
Some very recent boards do not suffer from this problem. For example all Solo's are fine as are the XRacer (aka PixRacer) boards.
Before panic ensues I'd like to say that although APM:Copter-3.3.2 is already 90% of this limit, remember we've just done a release and we will put effort into keeping the code size under 1MB. So for example, I can guarantee that APM:Copter-3.4 will fit and hopefully Copter-3.5 too.
Still, when you're shopping for your next Pixhawk you may consider asking the manufacturer if they are using the latest Rev3 STM32F427 processor.
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If you're doing it correctly you'll get a bunch of output, it just won't include the warning message.
Sorry, warning msg (not err msg) as Randy shows 1Mb limit. my new pix have short updating life but I'm in favor to new progress.
Cala, I agree with you, I am also in favour of progress, I do not understand people in this hobby complaining to buy a new autopilot once every few years because the old one is getting obsolete due to progress (and we are talking about 200$). How much is the autopilot % of the whole UAV frame?
Cala,
Thanks for checking.
Knowing which manufacturers (if any) are using RevC is important because I think this will lead to more manufacturers switching to use the RevC chip. We've got a lot of boards out there that are RevA so we need to start the process of increasing the percentage using RevC.
At the same time, we shouldn't panic. The other developers and I will do our best to keep the firmware under 1MB and I think there's a good amount of time before this issue really becomes a problem. I think it's at least a year before we start struggling, it could be two.. I'm not sure.
Once we hit the limit we will need to devote more effort to keeping the code small and worst case disabling features that take too much space and are rarely used. We could also create different versions of the firmware for the RevA vs RevC CPUs.
Thanks Randy. I know I'm preaching to the choir here, but I'm hopeful that various techniques that have worked for problems like this in other contexts will be effective in this instance once the limit becomes a significant problem. As I mentioned above, the presence of the older chips in the pipeline could be a problem for years. In analogous situations, I've had older versions of chips show up in devices several years after they not only were superseded by the chip manufacturers, but also several years after the device manufacturers using the chip series had certified they had moved to the new version. Ouch.
L
The bootloader for the FMUv4 systems will not allow the code to go onto a <Rev3 chip, so manufacturers should be able to prevent this. If they care to.
Many thank's Randy, I have the rest of my vehicles with APM yet, it's usefull to know this to replace with Rev C ones when I do it..
It would be great if older boards would be supported in the future. However, new boards will also have new sensors. So switching over to new hard- and firmware from time to time might be a good idea. There also seems to be a chance that updated Pixhawks and clones will become available so it would just be a simple replacement without the need for new cables, connectors etc.
A more general solution would be if certain modules could be switched on and off depending on the board. This would reduce functionality for older boards to some degree but provide up-to-date firmware for these.
I suggest not to get rid of USB. This is the only fast option to download the logs which are becoming bigger and bigger. So the suggested USB at Boot idea should be preferred. How much flash could be saved in this case?
I think that we have an established history of doing our best to support older hardware. But the community should recognize the fact that supporting older hardware, does create a significant extra workload for the developers. So the question becomes, how much of our limited resources should we devote to maintaining older hardware, and how much should we devote to developing new features which can only run on newer hardware? If we had 100 full-time developers, we wouldn't have as much trouble, but that's just not the reality.
Back in the waning days of APM-class hardware, I'd estimate nearly 90% of developer's time was spent trying to squeeze the code onto hardware that was obsolete. Counting bytes, converting floats to ints, etc. It really slowed development.
Personally, I'd rather not get back to that. I think that with 3.3, or 3.4, or 3.5, we should be satisfied to declare the code feature-complete for the Pixhawk-1 class of hardware, and move on. It's not the same situation as it was with APM-class hardware, where the firmware was barely capable of delivering what the hardware vendors promised. The latest Ardupilot firmware is the highest performance, most feature rich, and widely used firmware available, and it runs on hardware that is very affordable compared to the competition. I don't think there should be any shame declaring this generation is finished, and moving on to the next.
When we finally decided to discontinue APM-class development, there was much criticism from some in the community about their perception of loss of their "investment". Meanwhile, Pixhawk had been on the market for over a year, languishing, before any serious development work was done which took advantage of it's capabilities. In this fast-paced industry, that's just not competitive, and I think we fell behind a little bit.
There was talk that somebody should pick up the APM-class firmware development and continue it. We agreed to allow that. But to date, no serious effort has occurred. To me it's an indication that anybody with the skills and resources to do so, recognizes that it's an irrational thing to do.
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