Roomba Hack - Uart Questions

Question

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)

Robot Doc · Answer

The bit positions all have a decimal weight.

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

fredebec · Answer

Thanks @Robot Doc.

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?

DJ Sures · Answer

Use GetBit()
 $x = 2 if (getbit($x, 0)) print("Bump Right") endif if (GetBit($x, 1)) print ("Bump Left") endif if (GetBit($x, 2)) print ("Wheel Drop Right") endif if (GetBit($x, 3)) print ("Wheel Drop Left") endif

Dunning-Kruger · Answer

I am at work now.... i will check this thread later when i get home.... i think this script i wrote for the 400 series roomba.... i think the baud rate is wrong for the 600 series. .. @Doc can help you too after all he is the roomba doctor

Dunning-Kruger · Answer

That script is a little rough... and the baud rate is wrong. It should be 115200 not 57600... The 600 series uses 115200 baud.... also you only need to initialize the UART once.....

fredebec · Answer

@Richard' you are right. I already have modify baud rate and, as I said, the script works just fine (that's why it is not "required assistance thread" ).

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

Dunning-Kruger · Answer

@fredebec... Ok no worries..... I have another script that can read 2 byte data like Roomba battery voltage.... I'll post it for you tomorrow (my time) afternoon when I get home from work...

Robot Doc · Answer

fredebec Quote: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?  Yes, you got it !

fredebec · Answer

@DJ, 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.

Dunning-Kruger · Answer

@fredebec Here's another example for getting the roomba's battery voltage and charge state.... This example is using UART 0, however...
 uartinit(0, 0, 115200) #initialize UART port 0 sleep(100) $RX_DATA=0 uartWrite(0,0,142,22) # Volatge check sleep(50) uartWrite(0,0,142,21) # charge state sleep(50) $rx = UartAvailable(0, 0) if ($rx=3) $RX_DATA = UARTRead(0, 0, $rx) $MSB=GetByteAt($RX_DATA,0) $LSB=GetByteAt($RX_DATA,1) $Charge=GetByteAt($RX_DATA,2) $voltage=($LSB+(256*$MSB))/1000 print("Battery Voltage = "+$voltage) if ($charge=0) print("Roomba is not charging") elseif($Charge=1) print("Roomba is recondioning charging") elseif($Charge=2) print("Roomba is fast charging") elseif($Charge=3) print("Roomba is trickle charging") elseif($Charge=4) print("Roomba is waiting to charge") elseif($Charge=5) print("Roomba is not charging/Fault") endif endif

Robot Doc · Answer

Quote:The function is GetBit(Value, Bit). Why the value is $x=2 in that case ? The value of $x=2 just means that if bit position two is set to a 1 then "Wheel drop right" should be happening.

fredebec · Answer

@Robot Doc, now I think I am lost again 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 ?

fredebec · Answer

@Richard, thanks for the script. I will test it as soons as I can.

Robot Doc · Answer

Each bit position represents the state of a single sensor. If the bit position is storing a 0 then the sensor is off. If the bit position is storing a 1 the the sensor is on.

DJ Sures · Answer

I just used a $x to set a fake value to demonstrate the rest of the code. It's merely a place holder for the demo to run.

fredebec

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