Added Mbed 2 to Mbed OS bare metal porting guide #1293
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Waiting for engineering review |
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Looks good - thanks! |
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| - It might be necessary to reduce the stack size allocated for your target if it does not have enough RAM. The stack size is configured by setting a value for the `boot-stack-size` attribute; this value must be a multiple of 8 for alignment purposes. By default all targets are configured to have a boot stack size of 0x1000 (4096 bytes) in bare metal. However, this must be overridden if inadequate for your target. We recommend to reduce the boot stack size to 0x400 (1096 bytes) if your target has 8KB of RAM and to 0x300 (768 bytes) if your target has 4KB of RAM. |
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I'm not convinced, as far as I remember bare metal has only one stack. So the boot stack is the thread stack as well and the ISR stack.
0x400 (1096 bytes) if your target has 8KB of RAM
7K for global data and heap seems excessive. Also we'd like to have the applications pretty much portable if the stacks are different between different boards. The initial idea was that boards won't be allowed to play with stack sizes, only applications will be allowed to change them.
0x300 (768 bytes) if your target has 4KB of RAM.
Is it even possible to run Mbed on 4k board? Considering it's probably 8-16k flash...
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I'm not convinced, as far as I remember bare metal has only one stack. So the boot stack is the thread stack as well and the ISR stack.
0x400 (1096 bytes) if your target has 8KB of RAM
7K for global data and heap seems excessive. Also we'd like to have the applications pretty much portable if the stacks are different between different boards. The initial idea was that boards won't be allowed to play with stack sizes, only applications will be allowed to change them.0x300 (768 bytes) if your target has 4KB of RAM.
Is it even possible to run Mbed on 4k board? Considering it's probably 8-16k flash...
You are right that in bare metal the boot stack is the thread stack as well and the ISR stack. And that stack is defined to be 4K by default in https://github.com/ARMmbed/mbed-os/blob/master/targets/targets.json/#L60. For ultra constrained devices, it needs to be lowered.
LPC1114FN28: Flash 32kB, RAM 4kB was ported to bare metal ARMmbed/mbed-os@90d7e62; the recommendation to set boot-stack-size to 0x300 comes from that port.
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OK, but this is an extreme example with target that small it doesn't make much sense to run Mbed and it makes even less sense for us to spend time on making it work. I'm afraid that this exceptions will lead to a mess when people see "oh you can do that as it's already done for this target". It would be more than reasonable to say that we require at least 32/48K of ROM and at 8K of RAM. How big is bare metal blinky these days?
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| - It might be necessary to reduce the stack size allocated for your target if it does not have enough RAM. The stack size is configured by setting a value for the `boot-stack-size` attribute; this value must be a multiple of 8 for alignment purposes. By default all targets are configured to have a boot stack size of 0x1000 (4096 bytes) in bare metal. However, this must be overridden if inadequate for your target. We recommend to reduce the boot stack size to 0x400 (1096 bytes) if your target has 8KB of RAM and to 0x300 (768 bytes) if your target has 4KB of RAM. |
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I'm not convinced, as far as I remember bare metal has only one stack. So the boot stack is the thread stack as well and the ISR stack.
0x400 (1096 bytes) if your target has 8KB of RAM
7K for global data and heap seems excessive. Also we'd like to have the applications pretty much portable if the stacks are different between different boards. The initial idea was that boards won't be allowed to play with stack sizes, only applications will be allowed to change them.
0x300 (768 bytes) if your target has 4KB of RAM.
Is it even possible to run Mbed on 4k board? Considering it's probably 8-16k flash...
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I have addressed all review comments. Could you please re-review? |
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I will take another look at it on the preview branch to make sure all formatting works
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Waiting on 6-beta release to merge and publish. |
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Code related PRs are all merged to master so you can merge this PR. |
* Added Mbed 2 to Mbed OS bare metal porting guide * Apply suggestions from code review * Tidying up I will take another look at it on the preview branch to make sure all formatting works * Wording fix Co-authored-by: Irit Arkin <[email protected]>
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