DMA HW triggering at fixed frequency

Hi Matteo

The DMA request is triggered as a side effect of certain N2HET instructions, so you actually include the DMA request in the N2HET code that you write as a field in the instruction.

If you are using the LS03x series;  there is no DMA module on the device.  There is however an HTU tied to the N2HET that is a DMA dedicated to N2HET.

The triggering mechanism for HTU v.s. DMA is still the same - part of the instruction field of certain instructions.

There is an appnote SPNA130a that you can start with.  I believe it was written for the LS31x series so it may need a little mod to make it work on LS03x but it will get you going.

-Anthony

EDIT: Correction to link

Hi Antony,

thank you for the answer but your link is broken, can you please control it?

In the mean time can you brefly explain how to setup the HET2 (because the HET1 DOUT is the target of my data transfer) to emit the right trigger frequency? Should I setup a PWM for a square wave and act on some other registers to enable DMA trigger?

Can the procedure be done in HalCoGen or does it requires HET assembler programming?

thank you,

Matteo

Hi Matteo.

I fixed the link above.   You will need to customize the HET assembly program.  HalCoGen does have a way to import a HET program that you write so in this sense yes you can do this with HalCoGen but you will also need to modify the HET assembler program you are using to generate the request as the appnote shows.

There is a code download .zip file that goes with the appnote.  I'm not at a machine at the moment that can download this (traveling) but I expect that you will see additional HTU and HET configuration register writes that are probably not supported in HalCoGen's GUI today.    Like other modules for some of the more advanced configurations you can get most setup in HalCoGen but have sometimes to write to a few additional registers using the register .h file definitions that come with halcogen...

I don't think I understand the quewstion regarding HET2 v.s. HET1 because the LS03x only has a single HET module.   But generally you can chose to make the instruction that toggles the pin also generate a request, or you could use two separate instructions (one for the pin, the other for the request) with some time delay.  It all depends on what you are trying to accomplish.   If you just want to automatically DMA the period for the next PWM when you toggle the pin at the end of the current PWM you can probably use the same instruction.  But you might want to consider that there will be delay from the DMA generation to the HTU write.   So you might want to construct your HET program so that after the pin toggle,  there is a copy from a 'buffer' location in the N2HET RAM to the PWM next period, so that this 'next' period will be in place at the start of the next loop resolution guaranteed.   Then trigger an HTU request using a separate instruction to update this buffer location.   In this way your program will be able to tolerate more latency between the HTU and the memory system  but it also will add latency in the sense that the updates the CPU makes to the RAM buffer will take up to two loop resolution periods to make it to the PWM pin.  

This is something you'll need to decide as a strategy as appropriate for your application.   If you have a very tight loop resolution though, like /8 or /16, I think the double buffer is probably a must.

Anyway this is probably something you can decide after you get started - I'd start w. the example to get an understanding of how this works and then we can discuss more the best strategy for your particular app.

Best Regards,

-Anthony

Hi Antony,

inside HalCogen I can see two different HET1 and HET2 with separate driver enable check, pinmux settings and two separate tabs for functions settings. Doesn't this mean they are two separate devices?

About my problem: what I need is simply to generate a HW trigger for DMA. Ignoring that the target is to write the DOUT register: the only way to trigger DMA at a fixed frequency involves HET assembler (and is undocumented in the Technical reference)? There's no simpler way? I'm surprised.

Matteo