RCP 802.15.4 Firmware¶

Radio Co-Processor (RCP) firmware for the EFR32MG1B232F256GM48 chip found in the Lidl Silvercrest Smart Home Gateway.

This firmware transforms the gateway's Zigbee chip into a Radio Co-Processor that handles only the 802.15.4 PHY/MAC layer. The protocol stack runs on the host side, enabling two usage modes:

Mode	Stack	Host	Details
Zigbee (cpcd + zigbeed)	EmberZNet	External PC/RPi via serialgateway	See Host Software Setup
Thread (OTBR)	OpenThread	Natively on the RTL8196E gateway	See `3-Main-SoC.../34-Userdata/ot-br-posix/`

About RCP Architecture¶

Unlike standalone firmware (like the Router), an RCP delegates the entire Zigbee protocol stack to a host computer. The EFR32 only handles the radio PHY/MAC layer and communicates with the host via the CPC Protocol (Co-Processor Communication).

+-------------------+    UART     +-------------------+   Ethernet   +---------------------+
|  EFR32MG1B (RCP)  |   115200    |  RTL8196E         |    TCP/IP    |  Host (x86/ARM)     |
|                   |    baud     |  (Gateway SoC)    |              |                     |
|  802.15.4 PHY/MAC |<----------->|                   |<------------>|  cpcd               |
|  + CPC Protocol   |   ttyS1     |  serialgateway    |   port 8888  |    |                |
|                   |             |  (serial->TCP)    |              |    v                |
|  CPC Protocol v5  |             |                   |              |  zigbeed            |
|  HW Flow Control  |             |                   |              |  (Zigbee stack)     |
|                   |             |                   |              |    |                |
+-------------------+             +-------------------+              |    v                |
                                                                     |  Zigbee2MQTT        |
                                                                     +---------------------+

Why use RCP instead of NCP?

Aspect	NCP (24-NCP-UART-HW)	RCP (this firmware)
Stack location	On EFR32 (limited RAM)	On host (unlimited resources)
Protocol	EZSP (binary)	CPC (multiplexed)
Multiprotocol	No	Yes (Zigbee + Thread)
Stack updates	Requires reflash	Just update zigbeed
Network size	Limited by EFR32 RAM	Host memory is the limit

Hardware¶

Component	Specification
Zigbee SoC	EFR32MG1B232F256GM48
Flash	256KB
RAM	32KB
Radio	2.4GHz IEEE 802.15.4
UART	PA0 (TX), PA1 (RX), PA4 (RTS), PA5 (CTS) @ 115200 baud

Option 1: Flash Pre-built Firmware (Recommended)¶

Pre-built firmware is available in the firmware/ directory. From the repository root:

./flash_efr32.sh <GATEWAY_IP>
# Select [3] RCP-UART-HW

The script handles everything (serialgateway restart, flash, reboot).

Then continue to Host Software Setup to configure cpcd and zigbeed on your host machine.

Option 2: Build from Source¶

For users who want to modify the CPC configuration, change baudrate, or use a different SDK version.

Prerequisites¶

Install Silicon Labs tools (see 1-Build-Environment/12-silabs-toolchain/):

cd 1-Build-Environment/12-silabs-toolchain
./install_silabs.sh

This installs: - slc-cli - Silicon Labs Configurator - arm-none-eabi-gcc - ARM GCC toolchain - commander - Simplicity Commander - Gecko SDK with EmberZNet

Build¶

cd 2-Zigbee-Radio-Silabs-EFR32/25-RCP-UART-HW
./build_rcp.sh

Output¶

firmware/
└── rcp-uart-802154.gbl   # For UART/Xmodem flashing

Customization¶

Edit patches/rcp-uart-802154.slcp for SDK configuration, or patches/sl_cpc_drv_uart_usart_vcom_config.h for UART settings (pins, baudrate).

Flash¶

Via network (same as Option 1):

./flash_efr32.sh <GATEWAY_IP>
# Select [3] RCP-UART-HW

Via J-Link/SWD (if you have physical access to the SWD pads):

commander flash firmware/rcp-uart-802154.gbl \
    --device EFR32MG1B232F256GM48

For a detailed explanation of how universal-silabs-flasher works (firmware detection, bootloader entry, the -f flag, troubleshooting), see 22-Backup-Flash-Restore.

Host Software Setup¶

After flashing the RCP firmware, you need to configure the host software chain.

Required Components¶

Component	Version	Source	Description
cpcd	v4.5.3	SiliconLabs/cpc-daemon	CPC daemon
zigbeed	EmberZNet 8.2.2	Simplicity SDK 2025.6.2	Zigbee stack daemon (recommended)
zigbeed	EmberZNet 7.5.1	Gecko SDK 4.5.0	Zigbee stack daemon (legacy)

Build Instructions¶

See subdirectories for detailed build instructions: - cpcd/ - CPC daemon (for host) - zigbeed-8.2.2/ - zigbeed EmberZNet 8.2.2 (recommended) - zigbeed-7.5.1/ - zigbeed EmberZNet 7.5.1 (legacy) - rcp-stack/ - Systemd service manager for the complete chain - cpcd-rtl8196e/ - Cross-compile cpcd for gateway (experimental)

Quick Start with Docker (Recommended)¶

A pre-built Docker image is available for PC (amd64) and Raspberry Pi (arm64):

# Pull the image
docker pull ghcr.io/jnilo1/cpcd-zigbeed:latest

# Or use the full stack with Zigbee2MQTT
cd docker/
# Edit docker-compose.yml: set RCP_HOST to your gateway's IP
docker compose up -d

See docker/README.md for detailed instructions.

Image	cpcd	EmberZNet	EZSP	Architectures
`ghcr.io/jnilo1/cpcd-zigbeed:latest`	4.5.3	8.2.2	v18	amd64, arm64

Quick Start with rcp-stack (Native)¶

The rcp-stack tool manages the entire cpcd + zigbeed chain natively (without Docker):

# Start the stack
rcp-stack up

# Check status
rcp-stack status

# Stop the stack
rcp-stack down

# Troubleshoot
rcp-stack doctor

Zigbee2MQTT Configuration¶

With rcp-stack (recommended):

serial:
  port: /tmp/ttyZ2M
  adapter: ember

Baudrate and Network Considerations¶

Baudrate Options¶

Baudrate	Status	Notes
115200	Default	Conservative, reliable
230400	Supported	Tested, works reliably
460800+	Not supported	Causes UART overruns

Network Size vs Baudrate¶

Liaison	Throughput
802.15.4 radio	~25 KB/s
UART 115200	~11 KB/s
UART 230400	~23 KB/s

At 115200, the UART is ~2x slower than the Zigbee radio. Practical impact:

Network size	115200	230400
< 50 devices	OK	OK
50-100 devices	OK*	Recommended
> 100 devices	May bottleneck	Recommended

*OK for normal use; possible latency during traffic spikes (OTA updates, large groups).

For most home installations, 115200 is sufficient.

Why 460800+ Doesn't Work¶

The RTL8196E UART has hardware limitations: - 16-byte FIFO (16550A standard) with RX trigger at 8 bytes - At 460800 baud, the CPU has only 170 µs to respond before overrun - serialgateway runs in userspace, adding context switch latency

Check UART errors on the gateway:

cat /proc/tty/driver/serial
# fe:xxx = framing errors, oe:xxx = overrun errors

Changing Baudrate¶

To use 230400: 1. Edit patches/sl_cpc_drv_uart_usart_vcom_config.h 2. Edit patches/rcp-uart-802154.slcp 3. Rebuild firmware and flash 4. Update serialgateway -b 230400 on gateway 5. Update cpcd.conf with uart_device_baud: 230400

TCP Stability Requirements¶

The CPC protocol is sensitive to network conditions. For reliable operation:

Requirement	Why
Hardware flow control	Prevents buffer overruns
Direct Ethernet	Minimizes latency and jitter
No WiFi bridges	WiFi adds unpredictable latency
Avoid congested switches	Packet delays cause CPC timeouts

Recommended: Connect the gateway directly to the host with an Ethernet cable.

Troubleshooting¶

Flashing Issues¶

Problem	Solution
No response from RCP	Verify TCP: `nc -zv <gateway-ip> 8888`
Xmodem timeout	Close all SSH sessions, use `-f` flag
Wrong firmware flashed	Reflash - the bootloader is always preserved

cpcd Connection Issues¶

Problem	Solution
cpcd won't connect	Check `tcp_client_address` in cpcd.conf
CPC version mismatch	Use GSDK 4.5.0 for CPC Protocol v5
Frequent disconnects	Use direct Ethernet, check for WiFi bridges

zigbeed Issues¶

Problem	Solution
zigbeed won't start	Check cpcd is running: `rcp-stack status`
Stack version mismatch	Rebuild zigbeed with matching SDK version

Memory Usage¶

Resource	Used	Available
Flash	~116 KB	256 KB
RAM	~22 KB	32 KB

Features¶

RTL8196E Boot Delay: 1-second delay for host UART initialization
Hardware Flow Control: RTS/CTS required for reliable TCP operation
CPC Security Disabled: Saves ~45KB flash (not needed for local network)
Multiprotocol Ready: Can run Zigbee + OpenThread simultaneously

Project Structure¶

25-RCP-UART-HW/
├── build_rcp.sh                 # RCP firmware build script
├── README.md                    # This file
├── patches/                     # RCP firmware patches
│   ├── rcp-uart-802154.slcp                 # Project config
│   ├── main.c                               # Entry point (1s delay)
│   ├── sl_cpc_drv_uart_usart_vcom_config.h  # UART pins
│   └── sl_cpc_security_config.h             # CPC security disabled
├── firmware/                    # Output (rcp-uart-802154.gbl)
├── cpcd/                        # CPC daemon build scripts
├── zigbeed-7.5.1/               # zigbeed EmberZNet 7.5.1 (legacy)
├── zigbeed-8.2.2/               # zigbeed EmberZNet 8.2.2 (recommended)
├── docker/                      # Docker stack (cpcd + zigbeed + Z2M)
└── rcp-stack/                   # Systemd service manager
    ├── bin/rcp-stack            # Main script
    ├── scripts/                 # Helper scripts
    ├── systemd/user/            # Service units
    └── examples/                # Config examples

24-NCP-UART-HW/ - NCP firmware (simpler, stack on EFR32)
27-Router/ - Router firmware (autonomous, no host needed)

References¶

License¶

Educational and personal use. Silicon Labs SDK components under their respective licenses.