
fredebec
France
Asked
— Edited
Hi,
I have finally found a Roomba 620 I wish to use as a robot base. Everything works great, thanks to @RichardR examples and some very interesting threads.
Now I try to fully understand UART functions and the Roomba Open Interface, and sometimes it is a bit confusing... So, at this point I need some expert enlightenments.
Here is an example I don't understand:
Richard R made a script for object avoidance and it works great :
Quote:
:top
$drive=1
uartinit(0, 2, 57600) #initiate UART port 2 (pins 18 Tx and Pin 19 Rx)
sleep(20)
uartWrite(0, 2,128,132) #Init iRobot create and place in full mode
sleep(20)
uartWrite(0,2,137,0,125,128,0) #forward slow
$x=0
REPEATUNTIL($x>0)
uartWrite(0,2,142,7) #Roomba Bump and wheel drop sensor
IF (UARTAvailable(0,2)>0)
$x=UARTRead(0,2,1)
$x=GetByte($x)
ENDIF
print($x)
IF ($x=2) # left bumper hit
uartWrite(0,2,137,255,155,128,0) # back up
sleep(1000)
uartWrite(0,2,137,0,100,255,255) #turn right
sleep(2000)
ELSEIF ($x=1) # right bumper hit
uartWrite(0,2,137,255,155,128,0) # back up
sleep(1000)
uartWrite(0,2,137,0,100,0,1) #turn left
sleep(2000)
ELSEIF ($x>2) # centre bump or wheel drop
uartWrite(0,2,137,255,155,128,0) # back up
sleep(1000)
uartWrite(0,2,137,0,100,0,1,157,0,180,137,0,0,0,0) #turn around 180deg
sleep(2000)
ENDIF
sleep(20)
ENDREPEATUNTIL
goto(top)
But I don't understand the GetByte values: $x=2 correspond to "left bumper hit", $x=1 to "right bumper hit" and $x>2 to "centre bump or wheel drop"... but when I look at the OI documentation :

I don't see the fit with the bit values and I don't see how the Range could be 0-15 with only one byte...
Thanks for the help and sorry if it is a stupid question (I am afraid it will not be the last :D)
Bit position 0 set to binary 1 has a weight of 1
Bit position 1 set to binary 1 has a weight of 2
Bit position 2 set to binary 1 has a weight of 4
Bit position 3 set to binary 1 has a weight of 8
If all 4 bit positions are set then the decimal value would be 15. 1+2+4+8=15
All these "bit", "bytes", "16-bit values", "high bytes", "two’s complement" notions are completely new to me. But I think I get it...
So, to take the same example, if there is both a "Bump Left" and a "Wheel Drop Left", it will correspond to a bit position 1 (weight of 2) + a bit position 3 (weight of 8) and so, in the script, the $x value will be 10. Right?
Code:
But I want to better understand the way ARC and Roomba OI works together to go further in my future scripts, and your script was a good example to illustrate what I understand and what I don't...
@DJ, thanks for the tip and the script example
Yes, you got it !
Ok, I see why it is interesting to use GetBit(). But now, I don't understand where the $x=2 come from....
The function is GetBit(Value, Bit). Why the value is $x=2 in that case ?
Thank you all for your help.
@Richard, thank you for your scripts, it helps me a lot to have concrete examples.
Code:
The value of $x=2 just means that if bit position two is set to a 1 then "Wheel drop right" should be happening.
When you say "is set to 1", you mean "the state of the bumper/wheel drop is 1", with 0 ($x=1) = no bump/wheel raised and 1 ($x=2) = bump/wheel dropped.
Am I correct ?