osvein / tinygpu

High-level graphics processing unit for KS0108-based LCDs

TinyGPU

High-level graphics processing unit for KS0108-based LCDs

Instruction set

The 0th byte of an instruction consists of 8 bits. The 7 most significant bits identify the instruction. The least significant bit indicates whether it's a read or write operation (1 = read, 0 = write).

Name	0th byte
Status	0000 000x
Colour logic	0000 001x
Start line	0000 010x
Pixel	0000 100x
Polygon	0000 110x
Polyellipse	0000 111x

The exact behaviour of each instruction, including the difference between read and write operations, is explained below.

Status

1st byte:

	7 MSB	6	5	4	3	2	1	0 LSB
MOSI (w)							on/off	reset
MISO (w)
MOSI (r)
MISO (r)							on/off	idle

reset:

• 1 = soft reset GPU
  • LCD will be hard reset when the GPU is reset
• 0 = don't reset

on/off:

• 1 = connect LCD
  • has no effect if already connected
• 0 = disconnect LCD
  • has no effect if already disconnected
  • does not affect display data (i.e. will be redrawn when reconnected)

idle:

• 1 = idle - currently not processing and no operations are pending
• 0 = processing

Colour logic

1st byte:

	7 MSB	6	5	4	3	2	1	0 LSB
MOSI (w)							f(1)	f(0)
MISO (w)
MOSI (r)
MISO (r)							f(1)	f(0)

f(0): the resulting colour if the old colour is black

f(1): the resulting colour if the old colour is white

Start line

1st byte:

	7 MSB	6	5	4	3	2	1	0 LSB
MOSI (w)			line	line	line	line	line	line
MISO (w)
MOSI (r)
MISO (r)			line	line	line	line	line	line

line: the line at the top of the display

Pixel

1st byte:

	7 MSB	6	5	4	3	2	1	0 LSB
MOSI (w)	count	count	count	count	count	count	count	count
MISO (w)
MOSI (r)	count	count	count	count	count	count	count	count
MISO (r)

2nd byte:

	7 MSB	6	5	4	3	2	1	0 LSB
MOSI (w)		x	x	x	x	x	x	x
MISO (w)
MOSI (r)		x	x	x	x	x	x	x
MISO (r)

3rd byte:

	7 MSB	6	5	4	3	2	1	0 LSB
MOSI (w)			y	y	y	y	y	y
MISO (w)
MOSI (r)			y	y	y	y	y	y
MISO (r)	value

The 2nd and 3rd bytes are repeated count times in unsorted order. (i.e. 2nd-3rd-2nd-3rd-2nd-3rd for count = 3.)

count: the number of pixels

x: the x (horizontal) coordinate of the pixel

y: the y (vertical) coordinate of the pixel

value: the value of the pixel

Polygon

1st byte:

	7 MSB	6	5	4	3	2	1	0 LSB
MOSI (w)	count	count	count	count	count	count	count	count
MISO (w)

2nd byte:

	7 MSB	6	5	4	3	2	1	0 LSB
MOSI (w)		x	x	x	x	x	x	x
MISO (w)

3rd byte:

	7 MSB	6	5	4	3	2	1	0 LSB
MOSI (w)			y	y	y	y	y	y
MISO (w)

The 2nd and 3rd bytes are repeated count times in unsorted order. (i.e. 2nd-3rd-2nd-3rd-2nd-3rd for count = 3.)

The behaviour of reading is undefined.

count: the number of points

x: the x (horizontal) coordinate of the point

y: the y (vertical) coordinate of the point

Polyellipse

1st byte:

	7 MSB	6	5	4	3	2	1	0 LSB
MOSI (w)	radius	radius	radius	radius	radius	radius	radius	radius
MISO (w)

2nd byte:

	7 MSB	6	5	4	3	2	1	0 LSB
MOSI (w)	count	count	count	count	count	count	count	count
MISO (w)

3rd byte:

	7 MSB	6	5	4	3	2	1	0 LSB
MOSI (w)		x	x	x	x	x	x	x
MISO (w)

4th byte:

	7 MSB	6	5	4	3	2	1	0 LSB
MOSI (w)			y	y	y	y	y	y
MISO (w)

5th byte:

	7 MSB	6	5	4	3	2	1	0 LSB
MOSI (w)	arca	arca	arca	arca	arca	arca	arca	arca
MISO (w)

6th byte:

	7 MSB	6	5	4	3	2	1	0 LSB
MOSI (w)	arcb	arcb	arcb	arcb	arcb	arcb	arcb	arcb
MISO (w)

The 3rd, 4th, 5th and 6th bytes are repeated count times in unsorted order. (i.e. 3rd-4th-5th-6th-3rd-4th-5th-6th for count = 2.)

The behaviour of reading is undefined.

The behaviour of count>1 is undefined.

radius: the radius (in pixels)

count: the number of focal points

x: the x (horizontal) coordinate of the focal point

y: the y (vertical) coordinate of the focal point

arca: the start of the visible arc

arcb: the end of the visible arc

• linear, clockwise
  • 0 is above and on the same x coordinate as the focal point
  • 192 is on the left side of and on the same y coordinate as the focal point