P4 fixes

resources/espressif__esp_hosted/docs/shield-box-test-setup.md

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+# Shield Box Test Setup for ESP-Hosted
+
+Controlled RF environment for consistent throughput measurements and performance evaluation.
+
+## Overview
+
+**Shield Box Testing** uses RF-shielded enclosure to eliminate external interference and provide repeatable test conditions.
+
+**Key Benefits:**
+- Controlled RF environment (no external Wi-Fi/cellular interference)
+- Repeatable, consistent results
+- Better measurement accuracy vs open air
+
+
+## Equipment Required
+
+### Essential Components
+- **RF Shield Box/Chamber**: Faraday cage enclosure
+- **ESP32-P4 Function EV Board**: Host device
+- **ESP32-C6/C5 Test Board**: Co-processor device  
+- **External PC**: For iPerf client/server
+- **Router/Access Point**: Wi-Fi infrastructure
+- **Ethernet Connection**: Wired backhaul to PC
+
+Please change the host and co-processor nodes as per current use-case under test.
+
+## Test Setup
+
+### Physical Configuration
+
+<img src="images/PerformanceSetup-ShieldBox.png" alt="Shield box testing setup" width="800" />
+
+### Data Flow
+- **PC to MCU Host**:
+  ```
+  PC -> Router -> ESP Co-processor == SDIO/SPI/UART ==> ESP32-P4
+  ```
+- **MCU Host to PC**:
+  ```
+  PC <- Router <- ESP Co-processor <== SDIO/SPI/UART == ESP32-P4
+  ```
+
+**Traffic route:**
+- PC-to-Router: Ethernet with static IP (eliminates wireless variables)
+- Router-to-ESP: Wi-Fi connection (only wireless link in test chain)
+
+## Transport Configurations
+
+### SDIO (Highest Performance)
+- **Clock**: 20-50 MHz (start low, optimize up)
+- **Bus Width**: 4-bit mode
+- **Hardware**: External pull-ups (51kΩ) on CMD, D0-D3
+
+### SPI 
+- **Clock**: ESP32: ≤10 MHz, Others: ≤40 MHz
+- **Mode**: Full-duplex (simple) or Quad SPI (highest throughput)
+
+### UART
+- **Baud Rate**: 921600 (highest stable rate)
+- **Use Case**: Low-throughput validation, debugging
+
+
+## Shield Box vs Open Air
+
+| Aspect | Shield Box | Open Air |
+|--------|------------|----------|
+| **Repeatability** | High | Variable |
+| **Interference** | Eliminated | Present |
+| **Debugging** | Easier | Complex |
+| **Reality** | Lower | Higher |
+
+
+---
+
+*For transport setup details: [SDIO](sdio.md) | [SPI Full-Duplex](spi_full_duplex.md) | [SPI Half-Duplex](spi_half_duplex.md) | [UART](uart.md)*