SSD1307 dma

[AndrewCapon]

This also includes: #624

Added DMA transfers for data transfers to reduce cpu overhead.

display.h has a new pure virtual bool UpdateFinished(), returns true if the update has finished.

oled_display.h implements UpdateFinished() and calls the driver.

SSD130x4WireSpiTransport has been altered to support basic chained DMA via the finished callback, Config now has a useDma flag to enable DMA.

Some times:

Using SPI Prescaler = 2

Blocking
  1492.6 us total update time and Cpu

Dma
  Total update time = 1549.3us
  Cpu = (12.9us*16) + 0.3us = 206.7us

[github-actions]

Test Results

150 tests  ±0   150 ✅ ±0   0s ⏱️ ±0s
  1 suites ±0     0 💤 ±0 
  1 files   ±0     0 ❌ ±0 

Results for commit 432e4de. ± Comparison against base commit c695718.

♻️ This comment has been updated with latest results.

[stephenhensley]

Thanks for the contribution. This is a very welcome addition!

I briefly tested this on some hardware by modifying the included OLED_SSD130x4WireSPI example.

There were a few minor merge conflicts related to the dsy_pin -> Pin migration.
So I went ahead and fixed those up, and then retested before merging.