Document QEMU DHCP networking and add static IP option

QEMU provides a built-in DHCP server, but if there are issues,
static IP can be enabled as a fallback.

Documentation updates:
- Explained QEMU user-mode networking (slirp) provides DHCP
- Default network: 10.0.2.0/24, guest IP: 10.0.2.15
- Gateway: 10.0.2.2, DNS: 10.0.2.3
- Port forwarding: ESP32:80 → localhost:8080

Added static IP option in platformio.ini:
- Commented out by default (DHCP is preferred)
- Can be enabled if DHCP doesn't work
- Static IP 10.0.2.15 matches QEMU's default assignment
- Flags: WLED_STATIC_IP_DEFAULT_1 through _4

Updated documentation:
- docs/QEMU-ISSUES.md: Network configuration section
- e2e-tests/README.md: Troubleshooting ethernet/DHCP issues

DHCP should work by default in QEMU, but the static IP option
provides a fallback if connection issues occur.

Co-authored-by: softhack007 <[email protected]>

Author: Copilot

docs/QEMU-ISSUES.md

@@ -24,10 +24,36 @@ The build uses ESP32-POE board configuration (index 2):
 
 This configuration is compatible with QEMU's `open_eth` model, which emulates standard ESP32 RMII ethernet interface.
 
+### Network Configuration in QEMU
+QEMU's user-mode networking (slirp) provides:
+- **DHCP Server**: Built-in DHCP server (default network 10.0.2.0/24)
+  - Guest IP: 10.0.2.15 (assigned via DHCP)
+  - Gateway: 10.0.2.2
+  - DNS: 10.0.2.3
+- **Port Forwarding**: TCP port 80 on guest → port 8080 on host (localhost:8080)
+
+**DHCP vs Static IP:**
+- WLED normally uses DHCP on ethernet
+- QEMU provides a DHCP server by default
+- If DHCP doesn't work (connection issues), enable static IP in platformio.ini:
+  ```
+  -D WLED_STATIC_IP_DEFAULT_1=10
+  -D WLED_STATIC_IP_DEFAULT_2=0
+  -D WLED_STATIC_IP_DEFAULT_3=2
+  -D WLED_STATIC_IP_DEFAULT_4=15
+  ```
+- Static IP 10.0.2.15 matches QEMU's default guest IP assignment
+
 ## QEMU Limitations
 
 ESP32 QEMU emulation is not perfect and has several known limitations:
 
+### Network Configuration
+- **DHCP**: QEMU provides a built-in DHCP server (10.0.2.0/24 network)
+- **Expected behavior**: ESP32 should receive IP 10.0.2.15 via DHCP
+- **If DHCP fails**: Enable static IP in platformio.ini (see Build Configuration above)
+- **Port forwarding**: HTTP port 80 on ESP32 → localhost:8080 on host
+
 ### Hardware Emulation
 - **WiFi**: Not emulated - **causes crashes if enabled**
 - **Bluetooth**: Not emulated

e2e-tests/README.md

@@ -120,10 +120,17 @@ npx playwright show-report
 - Check QEMU logs: `cat qemu-output.log`
 - Verify firmware was built successfully
 
+**Ethernet/network connection issues:**
+- QEMU provides DHCP server (10.0.2.0/24 network, guest IP 10.0.2.15)
+- If DHCP fails, enable static IP in `platformio.ini` (see comments in file)
+- Check QEMU output for "ETH Connected" message
+- Port forwarding: ESP32 port 80 → localhost:8080
+
 **Tests fail with connection errors:**
 - Wait longer for ESP32 to boot (30-45 seconds minimum)
-- Check if port 80 is accessible: `curl http://localhost/`
+- Check if HTTP server started: `curl http://localhost:8080/`
 - Verify QEMU is still running: `ps aux | grep qemu`
+- Check for ethernet connection errors in QEMU logs
 
 **Tests timeout:**
 - QEMU emulation is slow - tests have 45 second timeouts
@@ -138,8 +145,10 @@ npx playwright show-report
 ## QEMU Limitations
 
 ESP32 QEMU emulation has limitations:
-- **Network**: User-mode networking only (no raw ethernet)
-- **WiFi**: Not emulated (returns mock data)
+- **Network**: User-mode networking with built-in DHCP (10.0.2.0/24)
+  - Guest IP: 10.0.2.15 (via DHCP or static configuration)
+  - Port forwarding: ESP32 port 80 → localhost:8080
+- **WiFi**: Not emulated (crashes if enabled - use ethernet build)
 - **Peripherals**: Many are stubbed (LEDs, I2C, etc.)
 - **Performance**: Slower than real hardware
 
@@ -148,6 +157,7 @@ Despite these limitations, QEMU is sufficient for testing:
 - JavaScript executes without errors  
 - API endpoints respond
 - Page navigation works
+- Ethernet networking works (via open_eth emulation)
 
 ## Adding New Tests
 

platformio.ini

@@ -1828,6 +1828,12 @@ build_flags = ${esp32_4MB_V4_S_base.esp32_build_flags}
   -D WLED_USE_ETHERNET
   -D WLED_ETH_DEFAULT=2 ;; ESP32-POE board configuration (works with QEMU open_eth)
   -D WLED_DISABLE_ESPNOW ;; ESP-NOW requires wifi, may crash with ethernet only
+  ;; Static IP for QEMU testing - user-mode networking provides DHCP at 10.0.2.0/24
+  ;; If DHCP fails, uncomment these lines to use static IP:
+  ; -D WLED_STATIC_IP_DEFAULT_1=10
+  ; -D WLED_STATIC_IP_DEFAULT_2=0
+  ; -D WLED_STATIC_IP_DEFAULT_3=2
+  ; -D WLED_STATIC_IP_DEFAULT_4=15
 lib_deps = ${esp32_4MB_V4_S_base.esp32_lib_deps}
     ${common_mm.HUB75_lib_deps}
 lib_ignore = IRremoteESP8266 ; use with WLED_DISABLE_INFRARED for faster compilation