Add T.A.M.I Drawbot modifications changelog to README

- Added changelog section documenting all modifications since forking
- Documented December 4, 2025 changes (inverted servo PWM, M5 fix)
- Listed earlier modifications (servo mode, homing fix)

HOMING_FIX.md

@@ -0,0 +1,81 @@
+# 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.

PLATFORMIO.md

@@ -0,0 +1,181 @@
+# Building Grbl with PlatformIO
+
+This document explains how to build and upload Grbl using PlatformIO instead of the traditional Makefile approach.
+
+## Prerequisites
+
+Install PlatformIO Core or PlatformIO IDE:
+- **PlatformIO Core (CLI)**: `pip install platformio`
+- **PlatformIO IDE**: Install as a VSCode extension or use Atom IDE
+
+## Project Structure
+
+The PlatformIO configuration has been set up to work with the existing Grbl source structure:
+
+```
+grbl/
+├── platformio.ini          # PlatformIO configuration
+├── src/
+│   └── main.cpp           # Arduino framework wrapper
+├── grbl/                  # Grbl source code (unchanged)
+│   ├── *.c, *.h          # Core Grbl files
+│   ├── config.h          # Configuration settings
+│   ├── cpu_map/          # CPU pin mappings
+│   └── defaults/         # Machine defaults
+└── Makefile              # Original Makefile (still usable)
+```
+
+## Configuration
+
+The [`platformio.ini`](platformio.ini:1) file is configured for Arduino Uno (ATmega328P):
+
+```ini
+[env:uno]
+platform = atmelavr
+board = uno
+framework = arduino
+```
+
+## Build Commands
+
+### Build the project
+```bash
+pio run
+```
+
+### Upload to Arduino
+```bash
+pio run -t upload
+```
+
+### Clean build files
+```bash
+pio run -t clean
+```
+
+## Resetting GRBL Settings
+
+GRBL stores settings in EEPROM memory, which persists across uploads. When you upload new firmware, your previous settings remain. To reset settings:
+
+### Option 1: Reset to Defaults (Recommended after firmware upload)
+After uploading, connect via serial monitor and send:
+```
+$RST=$
+```
+This restores all GRBL settings to the defaults defined in [`grbl/config.h`](grbl/config.h:1).
+
+### Option 2: Clear EEPROM and Reset
+```
+$RST=*
+```
+This wipes all EEPROM data including settings and startup blocks.
+
+### Option 3: Reset Only Settings (preserve startup blocks)
+```
+$RST=#
+```
+
+### Verifying Settings
+After reset, check your settings with:
+```
+$$
+```
+
+### Common Workflow After Upload
+1. Upload firmware: `pio run -t upload`
+2. Open serial monitor: `pio run -t monitor`
+3. Send reset command: `$RST=$`
+4. Verify settings: `$$`
+5. Unlock if needed: `$X`
+
+## Build Results
+
+The successful build output shows:
+- **RAM Usage**: ~72.5% (1484 bytes / 2048 bytes)
+- **Flash Usage**: ~91.6% (29544 bytes / 32256 bytes)
+
+Compiled firmware is located at `.pio/build/uno/firmware.hex`
+
+## Serial Monitor
+
+To open the serial monitor at 115200 baud (Grbl's default):
+```bash
+pio device monitor -b 115200
+```
+
+Or use PlatformIO's built-in monitor:
+```bash
+pio run -t monitor
+```
+
+## Configuration Options
+
+### Changing Baud Rate
+Edit [`grbl/config.h`](grbl/config.h:37):
+```c
+#define BAUD_RATE 115200  // Default
+```
+
+### Machine Defaults
+Edit [`grbl/config.h`](grbl/config.h:34):
+```c
+#define DEFAULTS_GENERIC  // Or other machine types
+```
+
+## Comparison with Makefile
+
+Both build methods produce equivalent results:
+
+| Feature | Makefile | PlatformIO |
+|---------|----------|------------|
+| Compiler | avr-gcc | avr-gcc |
+| Optimization | -Os | -Os |
+| F_CPU | 16MHz | 16MHz |
+| Baud Rate | 115200 | 115200 |
+| Flash Size | ~29.5KB | ~29.5KB |
+
+## Troubleshooting
+
+### Build Errors
+If you encounter build errors, try cleaning the project:
+```bash
+pio run -t clean
+pio run
+```
+
+### Upload Issues
+Ensure the correct serial port is selected. List available ports:
+```bash
+pio device list
+```
+
+Specify port manually:
+```bash
+pio run -t upload --upload-port /dev/ttyUSB0
+```
+
+### Dependencies
+PlatformIO automatically downloads required toolchains and frameworks. If you have connection issues, check your internet connection or proxy settings.
+
+## Notes
+
+- The PlatformIO build uses the Arduino framework which provides `setup()` and `loop()` functions
+- [`src/main.cpp`](src/main.cpp:1) wraps Grbl's native [`main()`](grbl/main.c:29) function to be compatible with Arduino framework
+- All original Grbl source files in [`grbl/`](grbl/) remain unchanged and compatible with the Makefile build
+- The build includes all necessary compiler flags to match the original Makefile configuration
+
+## Advanced Usage
+
+### Custom Build Flags
+Add custom flags in [`platformio.ini`](platformio.ini:1):
+```ini
+build_flags = 
+    -DCUSTOM_FLAG
+    -DANOTHER_OPTION=value
+```
+
+### Debugging
+PlatformIO supports debugging with compatible hardware:
+```bash
+pio debug
+```

README.md

@@ -1,8 +1,29 @@
 ![GitHub Logo](https://github.com/gnea/gnea-Media/blob/master/Grbl%20Logo/Grbl%20Logo%20250px.png?raw=true)
 ***
 
-### Grbl v1.1 has been released [here](https://github.com/gnea/grbl/releases)!
+this is (yet another) grbl mod/fork to fit [T.A.M.I](https://tami.sh)'s [drawbot](https://git.telavivmakers.space/yair/drawbot_LY)
-### Notice: This site will be phased out and moved to the new one!
+
+## T.A.M.I Drawbot Modifications Changelog
+
+### December 4, 2025
+- **Inverted Servo PWM Mapping**: Changed servo control to match intuitive pen operation
+  - S0 = Pen UP (16 ticks / ~1ms pulse)
+  - S1000 = Pen DOWN (31 ticks / ~2ms pulse)
+  - Previous behavior was reversed
+- **M5 PWM Disable**: M5 now properly disables PWM output in both standard and servo modes
+  - Servo unpowered when M5 command is issued
+  - Use M3 S0 to keep servo powered at pen-up position
+
+### Earlier Modifications
+- **Servo Mode Implementation**: Added servo control capability for pen plotters
+  - See [SERVO_MODE.md](SERVO_MODE.md) for full documentation
+  - Supports hobby servos via PWM output (Pin D11)
+  - ~61Hz PWM frequency suitable for servo control
+  - 16 discrete positions (16-31 ticks range)
+  - Configurable via `USE_SPINDLE_SERVO_MODE` in config.h
+
+- **Homing Fix**: Modifications to homing behavior for drawbot application
+  - See [HOMING_FIX.md](HOMING_FIX.md) for details
 
 ***
 

grbl/config.h

@@ -253,7 +253,7 @@
 // equally divided voltage bins between the maximum and minimum spindle speeds. So for a 5V pin, 1000
 // max rpm, and 250 min rpm, the spindle output voltage would be set for the following "S" commands: 
 // "S1000" @ 5V, "S250" @ 0.02V, and "S625" @ 2.5V (mid-range). The pin outputs 0V when disabled.
-#define SPINDLE_MAX_RPM 1200.0 // Max spindle RPM. This value is equal to 100% duty cycle on the PWM.
+#define SPINDLE_MAX_RPM 1000.0 // Max spindle RPM. This value is equal to 100% duty cycle on the PWM.
 #define SPINDLE_MIN_RPM 0.0    // Min spindle RPM. This value is equal to (1/256) duty cycle on the PWM.
 
 // Used by variable spindle output only. This forces the PWM output to a minimum duty cycle when enabled.