how keyboard firmwares work in Ruby psuedo-code

step_1.rb

# Step 1: A single key
require 'board'

## A key = row 2, pin 11

board.setInput(11) # Pin 11
board.setHigh(11) # Activate pullup resistor

# Set rows 0-3 outputs, and high:
[0, 1, 2, 3].each do |row|
  board.setOutput(row)
  board.setHigh(row)
end

# Set our row as low (ready to receive input)
board.SetLow(2)

call_c_func("usb_init")
sleep 0.2

while true do
  if board.low?(11)
    call_c_func("usb_send", 0, 4, 0, 0, 0, 0, 0)
    call_c_func("usb_send", 0, 0, 0, 0, 0, 0, 0)
  end
end


# It feels a bit backwards to treat high as deactivated and low as activated, but beacuse of the pullup resistors built-in to eac pin, this is the most convenient way to detect switch state. If it helps, you can think of "high" as having the key be in its "up" position and "low" as being pressed down, but of course this is not the actual reason.

step_2.rb

# Step 2: A full row
require 'board'
require 'keycodes'

include Keycodes

# Teensy pins
@column_pins = [11, 12, 18, 19, 10, 7, 8, 9, 5, 6]

@layout = [KEY_A, KEY_S, KEY_D, KEY_F, KEY_G,
          KEY_H, KEY_J, KEY_K, KEY_L, KEY_SEMICOLON]

# Set rows 0-3 outputs, and high:
[0..3].each do |row|
  board.setOutput(row)
  board.setHigh(row)
end
# Set row as low (ready to receive input)
board.SetLow(2)

@column_pins.each do |col_pin|
  board.setInput(col_pin)
  board.setHigh(col_pin) # Activate pullup resistor
end

call_c_func("usb_init")
sleep 0.2

def scan_column(col_pin, index)
  if board.low?(col_pin)
    code = @layout[index]
    call_c_func("usb_send", 0, code, 0, 0, 0, 0, 0)
  end
end


while true do
  @column_pins.each_with_index do |col, index|
    scan_column(col, index)
  end
end