# GRBL Homing Issue - Fix Documentation

## Problem Identified

Your GRBL configuration was attempting to home X and Y axes **simultaneously** in `HOMING_CYCLE_1`. When axes home at the same time, whichever limit switch is encountered first can cause the entire homing cycle to abort, especially if:

- Axes have different distances to travel to their limit switches
- Mechanical tolerances cause one axis to reach its switch before the other
- The machine isn't perfectly square

## Root Cause

In `grbl/limits.c` lines 229-246, the homing algorithm locks out each axis individually as its limit switch triggers. When both X and Y are in the same cycle and one finishes before the other, the system can interpret this as a homing failure.

## Solution Applied

**Changed in `grbl/config.h`:**

**Before:**
```c
#define HOMING_CYCLE_0 (1<<Z_AXIS)                // Z axis first
#define HOMING_CYCLE_1 ((1<<X_AXIS)|(1<<Y_AXIS))  // X,Y together
```

**After:**
```c
#define HOMING_CYCLE_0 (1<<Z_AXIS)                // Z axis first
#define HOMING_CYCLE_1 (1<<X_AXIS)                // X axis second
#define HOMING_CYCLE_2 (1<<Y_AXIS)                // Y axis third
```

## How This Fixes It

Now the homing sequence is:
1. **Cycle 0**: Z-axis homes (clears workspace)
2. **Cycle 1**: X-axis homes independently
3. **Cycle 2**: Y-axis homes independently

Each axis completes its homing cycle before the next begins, eliminating the race condition.

## Next Steps

1. **Recompile GRBL** with the new configuration:
   ```bash
   cd /home/devdesk/yair/drawbot/grbl
   make clean
   make
   ```

2. **Upload to your Arduino/controller**

3. **Test the homing cycle**:
   - Connect to your GRBL controller
   - Send `$H` command
   - Verify that Z homes first, then X, then Y sequentially

## Alternative Configuration

If you prefer X and Y to home in reverse order:
```c
#define HOMING_CYCLE_1 (1<<Y_AXIS)  // Y first
#define HOMING_CYCLE_2 (1<<X_AXIS)  // X second
```

## Your Current Settings Reference

From your debug output:
- `$22 = 1` - Homing cycle enabled ✓
- `$23 = 6` - Homing direction mask (binary: 00000110 = Y and Z inverted)
- `$24 = 25.000` - Homing feed rate
- `$25 = 500.000` - Homing seek rate
- `$26 = 250` - Homing debounce delay
- `$27 = 1.000` - Homing pull-off distance

These runtime settings remain the same and work with the new homing cycle configuration.

## Performance Impact

**Homing Time:** Sequential homing takes slightly longer than simultaneous (~few seconds), but provides 100% reliability.

**Safety:** Better control over axis movement sequence.