RGB565 SSD1351 driver fixed and tested.

drivers/ssd1351/README.md

@@ -1,12 +1,16 @@
 # Drivers for SSD1351
 
-There are two versions.
+There are three versions.
  * `ssd1351.py` This is optimised for STM (e.g. Pyboard) platforms.
  * `ssd1351_generic.py` Cross-platform version.
+ * `ssd1351_16bit.py` Cross-platform. Uses 16 bit RGB565 color.
 
-The cross-platform version includes the `micropythn.viper` decorator. If your
-platform does not support this, comment it out and remove the type annotations.
-You may be able to use the native decorator.
+To conserve RAM the first two use 8 bit (rrrgggbb) color. This works well with
+the GUI if saturated colors are used to render text and controls.
+
+The `ssd1351_generic.py` version includes the `micropython.viper` decorator. If
+your platform does not support this, comment it out and remove the type
+annotations. You may be able to use the `micropython.native` decorator.
 
 If the platform supports the viper emitter performance should still be good: on
 a Pyboard V1 this driver perorms a refresh of a 128*128 color display in 47ms.
@@ -16,5 +20,10 @@ of these figures is consumed by the data transfer over the SPI interface.
 If the viper and native decorators are unsupported a screen redraw takes 272ms
 (on Pyboard 1.0) which is visibly slow.
 
+The `ssd1351_16bit` version on a 128x128 display requires 32KiB for the frame
+buffer; this means it is only usable on platforms with plenty of RAM. Testing
+was done on a Pyboard D SF2W. With the GUI this version offers little benefit,
+but it delivers major advantages in applications such as rendering images.
+
 This driver was tested on official Adafruit 1.5 and 1.27 inch displays, also a
 Chinese 1.5 inch unit.

drivers/ssd1351/ssd1351_16bit.py

@@ -113,8 +113,10 @@ class SSD1351(framebuf.FrameBuffer):
                 self._write(mvb[start : start + bw], 1)  # Send a line
         else:
             for l in range(128):
-                if l < 96:
+                if l < 64:
                     start = (63 -l) * self.width * 2  # 63 62 .. 1 0
+                elif l < 96:
+                    start = 0
                 else:
                     start = (191 - l) * self.width * 2  # 127 126 .. 95
                 self._write(mvb[start : start + bw], 1)  # Send a line