Trying to get a VGA driver to work with FrameBuffer, but everything is shifted to the right

[ghost]

I'm trying to get this VGA driver for the Pi Pico to work with framebuf.FrameBuffer.

The original code uses 3 bits per pixel, stored in an array of 32-bit values. FrameBuffer does not support that format, so I modified the code to only use 1 bit per pixel. That way it should work with MONO_HMSB. And it does, except everything is shifted to the right by 32 pixels:

I only used one wire for color, and soldered it to both the green and red pins.

And here's my code:

from array import array
from gc import collect, mem_free
from framebuf import FrameBuffer, MONO_HMSB
from machine import Pin
from micropython import const
from rp2 import PIO, StateMachine, asm_pio
from uctypes import addressof


COLOR_PIN = Pin(2)
VSYNC_PIN = Pin(5)
HSYNC_PIN = Pin(4)
SCREEN_WIDTH = const(640)
SCREEN_HEIGHT = const(480)
PIXEL_BITMASK = const(0b1)
USABLE_BITS = const(32)
SM0_FREQ = 25175000
SM1_FREQ = 125000000
SM2_FREQ = 100700000


@asm_pio(set_init=PIO.OUT_HIGH, autopull=True, pull_thresh=32)
def _hsync():
	wrap_target()
	# ACTIVE + FRONTPORCH
	mov(x, osr)
	label('activeporch')
	jmp(x_dec, 'activeporch')
	# SYNC PULSE
	set(pins, 0) [31]
	set(pins, 0) [31]
	set(pins, 0) [31]
	# BACKPORCH
	set(pins, 1) [31]
	set(pins, 1) [13]
	irq(0)
	wrap()


@asm_pio(sideset_init=(PIO.OUT_HIGH,) * 1, autopull=True, pull_thresh=32)
def _vsync():
	pull(block)
	wrap_target()
	# ACTIVE
	mov(x, osr)
	label('active')
	wait(1, irq, 0)
	irq(1)
	jmp(x_dec, 'active')
	# FRONTPORCH
	set(y, 9)
	label('frontporch')
	wait(1, irq, 0)
	jmp(y_dec, 'frontporch')
	# SYNC PULSE
	wait(1, irq, 0).side(0)
	wait(1, irq, 0)
	# BACKPORCH
	set(y, 31)
	label('backporch')
	wait(1, irq, 0).side(1)
	jmp(y_dec, 'backporch')
	wait(1, irq, 0)
	wrap()


@asm_pio(
	out_init=PIO.OUT_LOW,
	out_shiftdir=PIO.SHIFT_RIGHT,
	sideset_init=PIO.OUT_LOW,
	autopull=True,
	pull_thresh=USABLE_BITS
)
def _mono_output():
	pull(block)
	mov(y, osr)
	wrap_target()
	mov(x, y).side(0)
	wait(1, irq, 1)
	label('colorout')
	out(pins, 1)
	nop()[1]
	jmp(x_dec, 'colorout')
	wrap()


@micropython.viper
def configure_DMAs(nword: int, screen_buffer_add: ptr32):
	# chan0 as 'configure' DMA and chan1 as 'data transfer' DMA
	# shared parameters
	IRQ_QUIET = 0
	RING_SEL = 0
	RING_SIZE = 0
	HIGH_PRIORITY = 1
	INCR_WRITE = 0

	# DMA channel 1
	TREQ_SEL = 2
	INCR_READ = 1
	DATA_SIZE = 2
	CHAIN_TO = 0
	EN = 1
	DMA_control_word = (
		(IRQ_QUIET << 21) | (TREQ_SEL << 15) | (CHAIN_TO  << 11) | (RING_SEL << 10) |
		(RING_SIZE << 9) | (INCR_WRITE << 5) | (INCR_READ << 4) | (DATA_SIZE << 2) |
		(HIGH_PRIORITY << 1) | (EN << 0)
	)
	ptr32(0x50000040)[0] = 0
	ptr32(0x50000044)[0] = uint(0x50200018)
	ptr32(0x50000048)[0] = nword
	ptr32(0x50000060)[0] = DMA_control_word

	# DMA channel 0
	TREQ_SEL = 0x3f
	INCR_READ = 0
	CHAIN_TO = 0
	EN = 1
	DMA_control_word = (
		(IRQ_QUIET << 21) | (TREQ_SEL << 15) | (CHAIN_TO  << 11) | (RING_SEL << 10) |
		(RING_SIZE << 9) | (INCR_WRITE << 5) | (INCR_READ << 4) | (DATA_SIZE << 2) |
		(HIGH_PRIORITY << 1) | (EN << 0)
	)
	ptr32(0x50000000)[0] = uint(screen_buffer_add)
	ptr32(0x50000004)[0] = uint(0x5000007c)
	ptr32(0x50000008)[0] = 1
	ptr32(0x50000010)[0] = DMA_control_word


@micropython.viper
def startsync():
	v = int(ptr16(SCREEN_HEIGHT))
	h = int(ptr16(SCREEN_WIDTH))
	sm_hsync.put(655)
	sm_vsync.put(int(v - 1))
	sm_mono_output.put(int(h - 1))
	ptr32(0x50000430)[0] |= 0b00001
	ptr32(0x50200000)[0] |= 0b111


sm_hsync = StateMachine(0, _hsync, freq=SM0_FREQ, set_base=HSYNC_PIN)
sm_vsync = StateMachine(1, _vsync, freq=SM1_FREQ, sideset_base=VSYNC_PIN)
sm_mono_output = StateMachine(
	2, _mono_output, freq=SM2_FREQ, out_base=COLOR_PIN, sideset_base=COLOR_PIN
)

screen_buffer = array('L', [0] * int(SCREEN_WIDTH * SCREEN_HEIGHT / USABLE_BITS))
screen_buffer_address = array('L', [addressof(screen_buffer)])
configure_DMAs(len(screen_buffer), screen_buffer_address)
startsync()
collect()

buf = FrameBuffer(screen_buffer, 640, 480, MONO_HMSB)
buf.fill(1)
buf.rect(0, 0, 640, 480, 0)
buf.text(f'{100 - round(mem_free() / 1024 / 264 * 100)}% of RAM in use', 1, 1, 0)

I must be missing something obvious, probably because I don't fully understand the original code. There's a lot of memory manipulation with magic numbers.

Note: Everything works perfectly fine if I modify the pixel array directly (which is what the original code does) instead of using FrameBuffer.

[czarnikjak]

Hi, did you ever resolved this issue?

[ghost]

No.