16-bit DMA #20
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16-bit DMA #20
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Using GPIOC 0-11, we move to a 16-bit wide (4 bits currently unused) frame buffer. This allows you to write 12 LED strands simultaneously (instead of only 8). On Teensy's where you have 16 contiguous GPIO ports on a single port (e.g. Port C), you could drive all 16 like this.
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This change moves to using GPIO port C (instead of GPIO port D) and drives up to 16 strands simultaneously (instead of 8). However, GPIOC on most Teensy's only exports 12 of those pins. One could support up to 15 on GPIOD with a Teensy 3.6. I've left it on GPIOC for now as those pins are slightly easier to solder to (through hole vs pad).
I don't suspect this branch is merge-able in its current state (none of the applications have been updated), but given that I've done this for a project that needed to drive 10 strands simultaneously using one Teensy, perhaps others might find it similarly useful to squeeze an extra 4-7 channels out of each Teensy.
For initializing displayMemory in an application/example, use
DMAMEM uint16_t displayMemory[STRAND_LEN*24];