Page 197 - Build Your Own Quadcopter_ Power Up Your Designs with the Parallax Elev-8

176 Bu il d Y o ur O w n Q u a d c o p t e r

{{
Theory of Operation:

Launch three cogs using the object RX which in turn each start two
counters. This approach does not need the pulses to arrive on the
pins in any certain order nor does it require all the pins to be
connected. Whatever pulse is received on pin 14 is then sent out to
pin 0 and so on.
}}

VAR
byte cog[3]
long stack[60]
long uS

PUB start(pins_array_address, pulsewidth_array_address) | i

uS := clkfreq/1_000_000

stop ‘call the stop method to stop
cogs that may be already started
repeat i from 0 to 2
cog[i] := cognew(readPins(@long[pins_array_address][i*2],
@long[pulsewidth_array_address][i*2]), @stack[i*20]) + 1

PUB stop | i
repeat i from 0 to 2
if cog[i]
cogstop(cog[i]~ -1)

PUB readPins (pins_address, pulsewidth_address) | i, p1, p2,
synCnt, active1, active2

repeat i from 0 to 1
spr[8+i] := %01000 << 26 + long[pins_address][i] ‘set the
mode and pin for ctra/b
spr[10+i] := 1 ‘set frqa/b

p1 := long[pins_address][0]
p2 := long[pins_address][1]
dira[p1]~
dira[p2]~
long[pulsewidth_address][0]~ ‘these lines ensure that the
0