DShot: updated driver to use NuttX DMA functions #13233
Conversation
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@Igor-Misic - Is DShot like one shot where there is only one pulse train sent per output cycle? |
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@davids5, yes. DShot drivers should be triggered externally (for example from the PID loop), but frequently enough that the ESC does not disarm motors. |
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@Igor-Misic - in that case I would expect to use the timers synchronously to the DMA not in repeat mode. Is that what is being done? |
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@davids5 - timers are used in burst mode (check TIMx_DMAR) and internal mechanisms take care that DMA is in synchronization with timer. We are only preparing data length, content and then we are enabling DMA and timer flag for DMA transaction. DMA then starts loading data to timer registers (CCR1 ... CCR4) over the DMAR register. All PWMs (DShot bits) are triggered at once. If there are 4 channels per timer it means it will be triggered 4x16 PWMs at once. |
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@Igor-Misic If the bust is completed, why is the fix for the missing/extra pulse to use a call back as opposed to just clear the UDE flag prior to the DMA set up/start call? |
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@davids5 DMA is not able to put the data in the timer before UDE is set. Setting UDE will start DMA transfer and timers at the same time. If we clean UDE in callback when transfer is complete we can be sure that next time when we call DShot again, timer and DMA will be in sync. Edit: yeah I got your point now. I think it will work even without a callback, sorry on delay xD |
… callback function
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@davids5 It works. It's a much cleaner solution. |
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Tested, didn't see any telemetry timeouts. Thanks for the simplifications @Igor-Misic
Can you rebase and update the modalai/fc-v1 board as well (#13259)?
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@bkueng do you consider this to be safe to go in to the release as well? |
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It should be, but as it's only a refactoring, there's no benefit and only risk in adding it. |
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Yer, I'm asking because I don't think we have a release branch yet, so we need to check. |
Switch from bare-metal driver to NuttX DMA driver.
The code looks cleaner and it is easier to port to other boards by using NuttX drivers.
DShot will use NuttX DMAMAP naming as other components.
Know issue explained:
The problem was happening because of timer peripheral was running freely. That caused unsynchronised the first DShot bits while DMA started filling the DMAR register. Sometimes there was a bit missing sometime there was an extra bit.
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Solution:
In burst mode, the timer trigger should be enabled after the DMA module. This is done with enabling UDE (Update DMA request enable) flag in timer after DMA is enabled. After DMA transfer is done UDE is disabled with the callback function because it needs to be disabled for the next cycle.