The Raspberry Pi Pico and micropython are new to me. I was curious to see how it would perform with graphics on an ST7735. From what I can see, the SPI output is just as fast as any other language however the preparation of SPI data is slower. I tried two approaches for writing filled rectangles to the display. The first prepared a bytearray filled with the desired colour values. This bytearray is then sent to the SPI bus with a single write command. From what I could see, the write is at full SPI speed with no gaps between bytes. The filling of the bytearray was a little slow.
The second approach involved sending the colour to the display in 2 byte blocks SPI. This eliminated the in-memory bytearray however it added a lot of CPU overhead. In the end I stayed with the first approach for now. I expect that I will be coming back to this in the future.
My initial demo was developed using the Thonny editor which is quite nice and looks like it may be suitable for STEM workshops.
The main function looks like this:
from machine import Pin, Timer,SPI
import urandom
import time
import st7735
display=st7735.st7735()
while(1):
x1=urandom.randint(0,120)
y1=urandom.randint(0,150)
x2=urandom.randint(0,120)
y2=urandom.randint(0,150)
w=urandom.randint(1,127-x1)
h=urandom.randint(1,159-y1)
colour=urandom.randint(0,65535)
display.drawLine(x1,y1,x2,y2,colour)
And the ST7735 library (for now) is this:
from machine import Pin, Timer,SPI
import time
class st7735:
def __init__(self):
# configure pins for output
self.reset=Pin(21,Pin.OUT)
self.cs=Pin(22,Pin.OUT)
self.a0=Pin(20,Pin.OUT)
self.spi=SPI(0,baudrate=20000000,polarity=1,phase=1,bits=8,firstbit=SPI.MSB,sck=Pin(18),mosi=Pin(19))
self.cs.value(1)
self.reset.value(1)
time.sleep_ms(10)
self.reset.value(0)
time.sleep_ms(200)
self.reset.value(1)
time.sleep_ms(200)
self.cs.value(200)
time.sleep_ms(200)
self.cs.value(0)
time.sleep_ms(20)
self.command(1) # software reset
time.sleep_ms(100)
self.cs.value(1)
time.sleep_ms(1)
self.cs.value(0)
time.sleep_ms(1)
self.command(0x11)
time.sleep_ms(120)
self.cs.value(1)
time.sleep_ms(1)
self.cs.value(0)
time.sleep_ms(1)
self.command(0xb1)
self.data(0x05)
self.data(0x3c)
self.data(0x3c);
self.cs.value(1)
time.sleep_ms(1)
self.cs.value(0)
time.sleep_ms(1)
self.command(0xb2)
self.data(0x05)
self.data(0x3c)
self.data(0x3c);
self.cs.value(1)
time.sleep_ms(1)
self.cs.value(0)
time.sleep_ms(1)
self.command(0xb3)
self.data(0x05)
self.data(0x3c)
self.data(0x3c)
self.data(0x05)
self.data(0x3c)
self.data(0x3c)
self.cs.value(1)
time.sleep_ms(1)
self.cs.value(0)
time.sleep_ms(1)
self.command(0xb4)
self.data(0x03)
self.cs.value(1)
time.sleep_ms(1)
self.cs.value(0)
time.sleep_ms(1)
self.command(0x36)
self.data(0xc8)
self.cs.value(1)
time.sleep_ms(1)
self.cs.value(0)
time.sleep_ms(1)
self.command(0x3a)
self.data(0x05)
self.cs.value(1)
time.sleep_ms(1)
self.cs.value(0)
time.sleep_ms(1)
self.command(0x29)
time.sleep_ms(100)
self.cs.value(1)
time.sleep_ms(1)
self.cs.value(0)
time.sleep_ms(1)
self.command(0x2c)
self.fillRectangle(0,0,128,160,0)
def command(self,cmd):
self.a0.value(0)
msg=bytearray()
msg.append(cmd)
self.spi.write(msg)
def data(self,cmd):
self.a0.value(1)
msg=bytearray()
msg.append(cmd)
self.spi.write(msg)
def openAperture(self,x1,y1,x2,y2):
self.command(0x2a)
self.data(x1 >> 8)
self.data(x1 & 0xff)
self.data(x2 >> 8)
self.data(x2 & 0xff)
self.command(0x2b)
self.data(y1 >> 8)
self.data(y1 & 0xff)
self.data(y2 >> 8)
self.data(y2 & 0xff)
self.command(0x2c)
def fillRectangle(self,x1,y1,w,h,colour):
self.openAperture(x1,y1,x1+w-1,y1+h-1)
pixelcount=h*w
self.command(0x2c)
self.a0.value(1)
msg=bytearray()
while(pixelcount >0):
pixelcount = pixelcount-1
msg.append(colour >> 8)
msg.append(colour & 0xff)
self.spi.write(msg)
def putPixel(self,x,y,colour):
self.openAperture(x,y,x+1,y+1)
self.a0.value(1)
msg=bytearray()
msg.append(colour >> 8)
msg.append(colour & 0xff)
self.spi.write(msg)
def drawLine(self,x0,y0,x1,y1,colour):
if ( (abs(y1-y0) < abs(x1-x0))):
if (x0 > x1):
self.drawLineLowSlope(x1,y1,x0,y0,colour)
else:
self.drawLineLowSlope(x0,y0,x1,y1,colour)
else:
if (y0 > y1):
self.drawLineHighSlope(x1,y1,x0,y0,colour)
else:
self.drawLineHighSlope(x0,y0,x1,y1,colour)
def drawLineLowSlope(self,x0,y0,x1,y1,colour):
# Reference : https://en.wikipedia.org/wiki/Bresenham%27s_line_algorithm
dx = x1 - x0
dy = y1 - y0
yi = 1
if (dy < 0):
yi = -1
dy = -dy
D = 2*dy - dx
y = y0
for x in range(x0,x1+1):
self.putPixel(x,y,colour)
if (D > 0):
y = y + yi
D = D - 2*dx
D=D + 2*dy
def drawLineHighSlope(self,x0,y0,x1,y1,colour):
# Reference : https://en.wikipedia.org/wiki/Bresenham%27s_line_algorithm
dx = x1 - x0
dy = y1 - y0
xi = 1
if (dx < 0):
xi = -1
dx = -dx
D = 2*dx - dy
x = x0
for y in range(y0,y1+1):
self.putPixel(x,y,colour)
if (D > 0):
x = x + xi
D = D - 2*dy
D=D + 2*dx
ioprog 