Hi, I'm also confused between trigger and request events, especially as they don't share the same sources.
The page 7 of the Application Note doesn't really help me.
But the figure 67 of the Reference Manual (RM0456, #17.4.13, rev5) is very interresting.
What I understand is that Request Events trigger the transfer of a single piece of data (single or burst), while Trigger Events request the initiation of the whole sequence. Right?
But what's happen if there are request events without any trigger? No transfer?
My use case is to sequentially copy a table to a GPIO port (and the section 3.7 of the application note is very short).
- For parallel communication with external devices
- For software PWMs (there isn't enough timer channels available in STOP 2, I need them for other purposes)
For (1), I need to start the frame transfer by software, while for (2), I need a continuously repeated sequence.
For both, I need a clock (typically a timer) to copy each cells of the table at the expected speed.
Unfortunately, software "event" is only available as a Request (through SWREQ), while there is very few timer sources available under Request events, for the LPDMA1 (lptim1_ue_dma and lptim3_ue_dma, but I use these timers for other purpose. I'm looking for LPTIM4, which is only available as a Trigger).
Alternatively, I can try to start the sequence via software by enabling the DMA channel, and trigger the transfer of a block of a single cell with lptim4_out. But I need the source address is automatically incremented and never reseted, untile the end of my table.
Otherwise, the transmission speed for (1) could be very fast (up to 200ns per cell, but above all no less) and without any constant rate contraints, since my table contains its own external clock. So, maybe I can try to tune the AHB clock bus to match that speed?
Thanks.
