Tiny Tapeout Scanchain Driver

scanchain-driver.py

from machine import Pin, Timer
import time

CLK_PERIOD_MS = 1
NUM_DESIGNS = 2 # should be higher

# from chip's perspective
# pinout here: https://projects.raspberrypi.org/en/projects/getting-started-with-the-pico/1
ext_clk =     Pin(6, Pin.OUT)
ext_latch =   Pin(7, Pin.OUT)
ext_scan =    Pin(8, Pin.OUT)
ext_data_in = Pin(9, Pin.OUT)  # data driven by us into the chip
ext_data_out = Pin(10, Pin.IN)  # data captured by us from the chip

# init
ext_data_in.value(0)
ext_latch.value(0)
ext_scan.value(0)
ext_clk.value(0)

# put data in: 00001111 to first design
ext_data_in.value(1)
for i in range(8):
    ext_clk.value(1)
    time.sleep_ms(CLK_PERIOD_MS)
    ext_clk.value(0)
    time.sleep_ms(CLK_PERIOD_MS)
    if i == 3:
        ext_data_in.value(0)

# latch data into the dut
ext_latch.value(1)
time.sleep_ms(CLK_PERIOD_MS)
ext_latch.value(0)
time.sleep_ms(CLK_PERIOD_MS)

# capture data by setting scan high and toggle the clock
ext_scan.value(1)
time.sleep_ms(CLK_PERIOD_MS)
ext_clk.value(1)
time.sleep_ms(CLK_PERIOD_MS)
ext_clk.value(0)
time.sleep_ms(CLK_PERIOD_MS)
ext_scan.value(0)

# drive data out through the chain
for i in range(8*NUM_DESIGNS):
    ext_clk.value(1)
    time.sleep_ms(CLK_PERIOD_MS)
    ext_clk.value(0)
    time.sleep_ms(CLK_PERIOD_MS)
    print(i, ext_data_out.value())