RSI-PI/templates/krl/README.md

KRL Coordination Templates

This directory contains KRL program templates demonstrating common Python-KRL coordination patterns using RSIPI.

Available Templates

1. basic_handshake.src

Simple I/O handshaking between Python and KRL

• KRL signals "ready" via digital output
• Python waits for signal, processes data
• Python signals "complete" via input
• KRL waits for completion, then continues

Use Case: Basic synchronization, ensuring Python completes processing before KRL continues.

Coordination Methods Used:

• api.krl.wait_for_signal(channel, timeout)
• api.krl.signal_complete(channel)

2. parameter_passing.src

Bidirectional numerical data exchange via Tech variables

• KRL writes current position to Tech.T variables
• Python reads position data
• Python calculates target and writes to Tech.C variables
• KRL reads target and executes motion

Use Case: Passing numerical parameters (positions, forces, tolerances) between Python and KRL.

Coordination Methods Used:

• api.krl.read_param(slot) - Read from Tech.T
• api.krl.write_param(slot, value) - Write to Tech.C
• api.krl.wait_for_signal(channel, timeout)
• api.krl.signal_complete(channel)

3. state_machine.src

Multi-state workflow with complex coordination

Implements a 5-state machine:

1. IDLE: Waiting to start
2. CALIBRATING: Python performing calibration
3. READY: Calibration complete
4. EXECUTING: Robot motion in progress
5. COMPLETE: Task finished
6. ERROR: Error handling state

Use Case: Complex workflows requiring multiple handshakes, error handling, and state tracking.

Coordination Methods Used:

• All coordination methods from basic_handshake and parameter_passing
• State variable in Tech.T[11]
• Command variable in Tech.C[11]

Python-KRL Coordination Patterns

Pattern 1: Simple Handshake

# Python side
api.krl.wait_for_signal(1)  # Wait for KRL ready signal
# Do processing...
api.krl.signal_complete(1)  # Signal KRL to continue

; KRL side
$OUT[1] = TRUE  ; Signal ready to Python
; Wait for Python completion
WHILE $IN[1] == FALSE
  WAIT SEC 0.1
ENDWHILE

Pattern 2: Parameter Exchange

# Python side
api.krl.wait_for_signal(1)

# Read from KRL
value = api.krl.read_param('T11')

# Process and write back
result = process(value)
api.krl.write_param('C11', result)

api.krl.signal_complete(1)

; KRL side
$TECH.T[11] = some_value
$OUT[1] = TRUE  ; Signal data ready

; Wait for Python
WHILE $IN[1] == FALSE
  WAIT SEC 0.1
ENDWHILE

; Read result
result = $TECH.C[11]

Pattern 3: Continuous Monitoring

# Python side - non-blocking monitoring loop
api.start()

while api.is_running():
    state = api.krl.read_param('T11')

    if state == 1:  # Specific state
        # React to state change
        api.krl.write_param('C11', calculated_value)
        api.krl.signal_complete(1)

    time.sleep(0.1)  # Check every 100ms

api.stop()

; KRL side - updates state continuously
$TECH.T[11] = current_state

; Wait for Python response when needed
WHILE $IN[1] == FALSE
  WAIT SEC 0.1
ENDWHILE

calculated = $TECH.C[11]

Tech Variable Conventions

Tech.C Variables (Python → KRL)

"Control" variables - Python writes, KRL reads

Slot	Description	Example Usage
C11	Command/state	0=continue, 1=pause, 2=abort
C12-C14	Position offsets	X, Y, Z corrections
C15-C17	Target position	Calculated target coordinates
C18-C20	Process parameters	Speed, force, tolerance
C21+	Custom parameters	Application-specific data

# Python writes
api.krl.write_param('C11', 0)  # Command: continue
api.krl.write_param('C12', 5.0)  # X offset
api.krl.write_param('C13', -2.0)  # Y offset

; KRL reads
command = $TECH.C[11]
offset_x = $TECH.C[12]
offset_y = $TECH.C[13]

Tech.T Variables (KRL → Python)

"Transfer" variables - KRL writes, Python reads

Slot	Description	Example Usage
T11	Current state	State machine state number
T12-T14	Current position	X, Y, Z coordinates
T15-T17	Force/torque	Measured forces
T18-T20	Sensor readings	External sensor data
T21+	Custom data	Application-specific values

; KRL writes
$TECH.T[11] = current_state
$TECH.T[12] = $POS_ACT.X
$TECH.T[13] = $POS_ACT.Y
$TECH.T[14] = $POS_ACT.Z

# Python reads
state = api.krl.read_param('T11')
pos_x = api.krl.read_param('T12')
pos_y = api.krl.read_param('T13')
pos_z = api.krl.read_param('T14')

I/O Signal Conventions

Standard I/O Mapping

Signal	Type	Purpose
$OUT[1]	Output	KRL → Python state/ready signal
$IN[1]	Input	Python → KRL completion acknowledgement
$IN[2]	Input	Python → KRL error signal
$OUT[2]	Output	KRL → Python auxiliary signal

# Python I/O methods
api.krl.wait_for_signal(1)  # Wait for $OUT[1]
api.krl.signal_complete(1)  # Set $IN[1]
api.io.set_output(2, True)  # Control $OUT[2]

Error Handling Best Practices

Timeouts

Always use timeouts to prevent indefinite blocking:

# Python
if not api.krl.wait_for_signal(1, timeout=10.0):
    print("Timeout waiting for KRL!")
    # Handle error

; KRL
INT counter
counter = 0
WHILE ($IN[1] == FALSE) AND (counter < 100)
  WAIT SEC 0.1
  counter = counter + 1
ENDWHILE

IF counter >= 100 THEN
  ; Timeout - handle error
  HALT
ENDIF

Error Signaling

Use dedicated error channels:

# Python detects error
if error_condition:
    api.io.set_output(2, True)  # Signal error to KRL

; KRL checks for errors
IF $IN[2] == TRUE THEN
  ; Python signaled error
  HALT
ENDIF

Integration with RSI Motion Control

All coordination patterns work seamlessly with RSI real-time motion corrections:

# Python coordinates with KRL AND sends real-time corrections
api.start()

# Wait for KRL to start motion phase
api.krl.wait_for_signal(1)

# Send real-time corrections during KRL motion
for i in range(100):
    correction = calculate_correction()
    api.motion.update_cartesian(X=correction)
    time.sleep(0.004)  # 250Hz update rate

# Signal motion phase complete
api.krl.signal_complete(1)

api.stop()

; KRL executes motion while Python sends corrections
$OUT[1] = TRUE  ; Signal motion start

; Python sends corrections via RSI during this move
LIN target_pos Vel=0.5 m/s CPDAT1 Tool[1] Base[0]

; Wait for Python to finish corrections
WHILE $IN[1] == FALSE
  WAIT SEC 0.1
ENDWHILE

Testing Templates

To test these templates:

1. Upload KRL program to robot controller
2. Start Python coordination script
3. Execute KRL program on teach pendant
4. Monitor coordination in Python logs

Example Python test script:

from RSIPI import RSIAPI
import time

api = RSIAPI('RSI_EthernetConfig.xml')
api.start()

try:
    print("Waiting for KRL ready signal...")

    if api.krl.wait_for_signal(1, timeout=30.0):
        print("✅ KRL signaled ready!")

        # Simulate processing
        time.sleep(2.0)
        print("Processing complete")

        # Signal back to KRL
        api.krl.signal_complete(1)
        print("✅ Signaled KRL to continue")

    else:
        print("❌ Timeout waiting for KRL")

except KeyboardInterrupt:
    print("\n⚠️  Interrupted by user")

finally:
    api.stop()
    print("API stopped")

Troubleshooting

Signal Not Received

Check I/O configuration in RSI XML:

<SEND>
  <XML>
    <ELEMENT Tag="Digin" Type="INT"/>
  </XML>
</SEND>
<RECEIVE>
  <XML>
    <ELEMENT Tag="Digout" Type="INT"/>
  </XML>
</RECEIVE>

Tech Variable Not Found

Ensure Tech variables are configured in RSI XML:

<SEND>
  <XML>
    <ELEMENT Tag="Tech" Type="DOUBLE" Indizes="[1..199]"/>
  </XML>
</SEND>
<RECEIVE>
  <XML>
    <ELEMENT Tag="Tech" Type="DOUBLE" Indizes="[1..199]"/>
  </XML>
</RECEIVE>

Timing Issues

• Reduce check_interval for faster response: api.krl.wait_for_signal(1, check_interval=0.005)
• Increase timeout for slow operations: api.krl.wait_for_signal(1, timeout=60.0)
• Add WAIT SEC delays in KRL for signal propagation

Next Steps

After understanding these templates:

1. Adapt templates to your specific application
2. Test coordination patterns with your robot
3. Implement error recovery mechanisms
4. Document custom coordination protocols
5. Create application-specific state machines

References

• RSIPI Documentation
• Phase 3 Summary (when available)
• KUKA RSI 3.3 Documentation

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Template Author: RSIPI Development Team Last Updated: January 17, 2026 Version: 1.0