Build a FTM+DMA six pulse controler

[GabrielChies]

Good day,

I’m developing the pulse generator for a 3-phase SCR rectifier. To guarantee that each thyristor gate (and its complementary clear) happens at the exact instants, I built an “edge buffer” that holds, for each edge in one mains period, the GPIO address to touch and the timer tick at which that action must occur.

The timebase is FTM3 running in output-compare with MOD = 15624 (one 0…MOD ramp per 60 Hz mains period). I use channel 6 as the event source. Every time CNT == C6V, the channel issues a DMA request; that request drives a scatter/gather (S/G) ring on DMA channel A that performs exactly one 32-bit write to the specific GPIO register (set or clear) for that edge. All S/G descriptors are linked in a circle, so the list advances one step per compare event, forever.

Immediately after each GPIO write, I must also program the next compare instant so the following edge lands at the correct tick. For that I added minor-loop channel linking: channel A is configured to minor-link to DMA channel B. Each time A completes its one-word GPIO write, it triggers B to perform one half/word write to FTM3->CONTROLS[6].CnV with the next value from a 12-element table. Channel B’s TCD is a simple cyclic transfer over that table, so it advances one entry per link and then wraps to the start for the next mains period.

It all sounds good to go, but the problem is that the CH6 events are cyclic at the same rate as the FTM 60 Hz. There are two issues: CnV is not being updated through this method, and if I manage to update it, the counter goes back to 0 when it should keep counting from where it was. Effectively what I want is to trigger 12 DMA requests on a single run of the timer from 0 to timer MOD, which so far I cannot. Using the CH6 interrupt and some code I can fix the issue, but CH6 is disabled by the DMA CH6 request.

I am attaching the code for now. Any experts, that could help on the CNV update issue?

Best regards.

[Habib_MS]

Hello @GabrielChies,

In order to support you better, could you provide me the next information?

-The MCU you are using
-The IDE you are currently working with
-The SDK version used in your implementation

BR
Habib.

[GabrielChies]

Hi @Habib_MS,

Did you perhaps had a chance to look into this case?

BR.

[Habib_MS]

Hello @GabrielChies,

Yes, sorry for the late reply.

From what I can see, the logic you are using looks fine, so this might be more of a software issue. To help pinpoint the problem, could you check a few things?

-Are both DMA transfer callbacks being triggered? And are they doing what you expect?
-One possible issue could be that the time between each CnV change is too short, which might cause invalid data. Can you double check if the timing looks right?
-For debugging, you could try sending a message over UART or toggling a pin every time a callback is entered. That pin should ideally toggle 12 times per iteration.
Also, it might help to check the DMA status flags. Especially the Error Status Register in section 22.3.6 of the RM.

BR
Habib

[GabrielChies]

Hello @Habib_MS ,

Yes, both DMA transfer callbacks being triggered. About doing what are expect, the one that handles the GPIO write (channel A) is working fine, the other one seems unable to update the compare value of the FTM3 as it should (channel B). 

I think the issue might be FTM oriented not on the DMA, what I observed on the osciloscope debuging using pin toggle on each callback is that the sequence of the pins is right but the timming is not.

Instead of all the 12 GPIO's writes happening inside the time frame of the FTM3-MOD value, they are happening at 12 times the FTM3-MOD value. If i am right this means the second DMA channel is only beeing triggered at the overflow of the timer or always at the same point (say first edge value).

Thats what I have so far.

BR
Gabriel

[Habib_MS]

Hello @GabrielChies,

Please make sure that the FTM has DMA request enabled. This can be achieved using the function called FTM_EnableDmaTransfer.
I highly recommend checking the example called "frdmk64f_edma_channel_link", which shows how to configure a minor loop after a major loop request in order to identify any configuration you might be missing.
Please pay attention to the function called EDMA_TcdSetChannelLink, which is the one that links the minor loop with the major loop.

BR
Habib

[GabrielChies]

Hello good sir,

I am using the MK64FN1M0VLL12 microcontroler.
The IDE is the MCU Expresso 24.12.
And the SDK is the v2.11.0.

BR.

[GabrielChies]

Edit..
FTM is configured in the peripherals tools as follow.

static void FTM3_init(void) {
FTM_Init(FTM3_PERIPHERAL, &FTM3_config);
FTM_SetTimerPeriod(FTM3_PERIPHERAL, FTM3_TIMER_MODULO_VALUE);
FTM_SetupOutputCompare(FTM3_PERIPHERAL, kFTM_Chnl_6, kFTM_NoOutputSignal, 7812U);
FTM_EnableInterrupts(FTM3_PERIPHERAL, kFTM_Chnl6InterruptEnable | kFTM_TimeOverflowInterruptEnable);
/* Enable interrupt FTM3_IRQn request in the NVIC. */
EnableIRQ(FTM3_IRQN);
}