Espruino on P8 smartwatch - ST7789 display driver in Inline C

The performance when I rebuilt with DMA enabled was:

P8: fillRect 81ms, drawImage 154ms.

which is much more reasonable. However, I have now implemented double buffering which with two 60 pixel (120 byte ) buffers gives:

P8: fillRect 85ms, drawImage 111ms.

There is a tradeoff in that smaller buffers allow more overlap but increase the time to draw the rectangle - important for fast g.clear().

I would now like to get the driver to work with SPI Flash which I guess requires some care with the chip select pins?