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Additional Details about DMAMUX and TRGMUX in KL28?

Question asked by Mark Butcher on Nov 26, 2017
Latest reply on Nov 28, 2017 by Mark Butcher

Hi All


Does anyone know the KL28's DMAMUX/TRGMUX operation well enough to work out its details with respect to periodic DMA triggering based on LPIT channel(s)?


First of all I have tried to represent the operation in a simplified form as follows:

The periodic trigger functionality is available on the first 4 DMA channels (this is the case generally for Kinetis parts) and the single "always-on" slot is slot 63, called DMA MUX.
In other Kinetis parts the always on slots are connected to PIT sources but the KL28 seems to route via the TRGMUX to the LPIT, as is shown in the diagram (note that all other peripheral slots look to be connected directly to their corresponding peripheral trigger source).


The TRGMUX_DMAMUX0 is thus presumably dedicated to the DMA_MUX slot in the KL28. Also, this can connect to 4 trigger sources (SEL0, SEL1, SEL2 and/or SEL3), which can be either channels from the LPIT or various other peripheral triggers.


This all makes sense apart from the fact that I doubt that more than one trigger source would be used at a time (?)


The only reference that I can find to back this up is this extract from the user's guide:


This looks to confirm that the LPIT trigger really passes through the TRGMUX but it is confusing due to the following reasons:

1. It states that LPIT0 channel's 0 and 1 could be used, whereby the TRGMUX allows any of the 4 channels to be routed.
2. It limits to DMA channels 0 and 1 whereby periodic triggering should be possible on channel's 0 to 3.
3. It fixes LPT0 channel 0 with DMA channel 0 and LPT0 channel 1 with DMA channel 1, whereby there is only one (always on) DMA MUX slot, which should be able to connect to any DMA channel.

Therefore I am also wondering whether this extract is really correct or whether the table is a cut and paste from a different Kinetis part that has a fixed slot/channel/PIT source arrangement.

Any one with more details, explanations and/or experience with this?