diff --git a/drivers/gc9a01/gc9a01.py b/drivers/gc9a01/gc9a01.py
index 8df05db..95fc7e8 100644
--- a/drivers/gc9a01/gc9a01.py
+++ b/drivers/gc9a01/gc9a01.py
@@ -11,8 +11,7 @@ import asyncio
 from drivers.boolpalette import BoolPalette
 
 # Initialisation ported from Russ Hughes' C driver
-# https://github.com/russhughes/gc9a01_mpy/blob/main/src/gc9a01.h
-# https://github.com/russhughes/gc9a01_mpy/blob/main/src/gc9a01.c
+# https://github.com/russhughes/gc9a01_mpy/
 # Based on a ST7789 C driver: https://github.com/devbis/st7789_mpy
 # Many registers are undocumented. Lines initialising them are commented "?"
 # in cases where initialising them seems to have no effect.
@@ -21,7 +20,7 @@ from drivers.boolpalette import BoolPalette
 # Waveshare touch board https://www.waveshare.com/wiki/1.28inch_Touch_LCD has CST816S touch controller
 # Touch controller uses I2C
 
-# Portrait mode
+# Portrait mode. ~70μs on RP2 at standard clock.
 @micropython.viper
 def _lcopy(dest: ptr16, source: ptr8, lut: ptr16, length: int):
     # rgb565 - 16bit/pixel
@@ -84,7 +83,7 @@ class GC9A01(framebuf.FrameBuffer):
         sleep_ms(50)
         if self._spi_init:  # A callback was passed
             self._spi_init(spi)  # Bus may be shared
-        self._lock = asyncio.Lock()
+        self._lock = asyncio.Lock()  # Prevent concurrent refreshes.
         sleep_ms(100)
         self._wcd(b"\x2a", int.to_bytes(width - 1, 4, "big"))
         # Default page address start == 0 end == 0xEF (239)
diff --git a/drivers/ili93xx/ili9341.py b/drivers/ili93xx/ili9341.py
index def8194..99b3104 100644
--- a/drivers/ili93xx/ili9341.py
+++ b/drivers/ili93xx/ili9341.py
@@ -1,6 +1,6 @@
 # ILI9341 nano-gui driver for ili9341 displays
 
-# Copyright (c) Peter Hinch 2020
+# Copyright (c) Peter Hinch 2020-2024
 # Released under the MIT license see LICENSE
 
 # This work is based on the following sources.
@@ -15,16 +15,20 @@ import asyncio
 from drivers.boolpalette import BoolPalette
 
 
+# ~80μs on RP2 @ 250MHz.
 @micropython.viper
 def _lcopy(dest: ptr16, source: ptr8, lut: ptr16, length: int):
     # rgb565 - 16bit/pixel
-    n = 0
-    for x in range(length):
+    n: int = 0
+    x: int = 0
+    while length:
         c = source[x]
         dest[n] = lut[c >> 4]  # current pixel
         n += 1
         dest[n] = lut[c & 0x0F]  # next pixel
         n += 1
+        x += 1
+        length -= 1
 
 
 class ILI9341(framebuf.FrameBuffer):
diff --git a/drivers/ili94xx/ili9486.py b/drivers/ili94xx/ili9486.py
index 6f537da..d6955e9 100644
--- a/drivers/ili94xx/ili9486.py
+++ b/drivers/ili94xx/ili9486.py
@@ -1,6 +1,6 @@
 # ILI9486 nano-gui driver for ili9486 displays
 
-# Copyright (c) Peter Hinch 2022
+# Copyright (c) Peter Hinch 2022-2024
 # Released under the MIT license see LICENSE
 
 # Much help provided by @brave-ulysses in this thread
@@ -22,13 +22,16 @@ from drivers.boolpalette import BoolPalette
 @micropython.viper
 def _lcopy(dest: ptr16, source: ptr8, lut: ptr16, length: int):
     # rgb565 - 16bit/pixel
-    n = 0
-    for x in range(length):
+    n: int = 0
+    x: int = 0
+    while length:
         c = source[x]
         dest[n] = lut[c >> 4]  # current pixel
         n += 1
         dest[n] = lut[c & 0x0F]  # next pixel
         n += 1
+        x += 1
+        length -= 1
 
 
 # FB is in landscape mode, hence issue a column at a time to portrait mode hardware.
@@ -41,7 +44,7 @@ def _lscopy(dest: ptr16, source: ptr8, lut: ptr16, ch: int):
     n = 0
     clsb = col & 1
     idx = col >> 1  # 2 pixels per byte
-    for _ in range(height):
+    while height:
         if clsb:
             c = source[idx] & 0x0F
         else:
@@ -49,6 +52,7 @@ def _lscopy(dest: ptr16, source: ptr8, lut: ptr16, ch: int):
         dest[n] = lut[c]  # 16 bit transfer of rightmost 4-bit pixel
         n += 1  # 16 bit
         idx += wbytes
+        height -= 1
 
 
 class ILI9486(framebuf.FrameBuffer):