Bootloader-UART-Xmodem for Lidl Gateway¶

UART XMODEM bootloader for EFR32MG1B232F256GM48 (Lidl Silvercrest Gateway).

This bootloader enables firmware updates via UART using the XMODEM-CRC protocol, without requiring SWD/JTAG access.

Quick Start¶

# Build the bootloader
./build_bootloader.sh

# Flash via J-Link (combined = first stage + main stage)
commander flash firmware/bootloader-uart-xmodem-2.4.2-combined.s37 --device EFR32MG1B232F256GM48

Prerequisites¶

slc (Silicon Labs CLI) in PATH
arm-none-eabi-gcc in PATH
commander in PATH
GECKO_SDK environment variable set

Or use Docker from the 2-Zigbee-Radio-Silabs-EFR32 directory:

docker run -it --rm -v $(pwd)/..:/workspace lidl-gateway-builder \
    /workspace/2-Zigbee-Radio-Silabs-EFR32/23-Bootloader-UART-Xmodem/build_bootloader.sh

Build Process¶

1. Copy slcp + slpb from patches/
        ↓
2. slc generate
        ↓
3. Copy config headers from patches/
        ↓
4. make -Oz
        ↓
5. Post-build (commander convert/gbl create)

Hardware Configuration¶

UART Pinout (USART0)¶

Signal	Port	Pin	Description
TX	PA0	0	Transmit to RTL8196E
RX	PA1	1	Receive from RTL8196E

No hardware flow control (standard Simplicity Studio configuration).

Output Files¶

After running ./build_bootloader.sh, files are in firmware/:

File	Description
`bootloader-uart-xmodem-X.Y.Z.s37`	Main stage bootloader
`bootloader-uart-xmodem-X.Y.Z-crc.s37`	Main stage with CRC
`bootloader-uart-xmodem-X.Y.Z-combined.s37`	First stage + Main stage (for J-Link)
`bootloader-uart-xmodem-X.Y.Z.gbl`	GBL image (for XMODEM/UART upload)
`first_stage.s37`	First stage only

Using the Bootloader¶

Once flashed, the bootloader responds to serial commands at 115200 baud:

Command	Action
`1`	Start XMODEM transfer (upload new firmware)
`2`	Start application

To enter the bootloader: - Send serial break, OR - No valid application present

Understanding the 2-Stage Bootloader Architecture (Series 1)¶

EFR32MG1B (Gecko Series 1) devices use a two-stage bootloader system:

Stage 1 – First-stage bootloader (BSL)¶

Resides in main flash memory starting at address 0x0000
Minimal: verifies and launches Stage 2
Cannot be updated via UART or OTA
Can only be overwritten using SWD and a debugger

Stage 2 – Main bootloader¶

Resides in main flash memory starting at address 0x0800
Contains UART XMODEM functionality
Can be updated in the field via .gbl packages

Application¶

Resides in flash memory starting at address 0x4000
Updated via XMODEM using .gbl files

Memory Map¶

0x00000000 ┌─────────────────────────┐
           │  First Stage (2 KB)     │ ← Can only be updated via SWD
0x00000800 ├─────────────────────────┤
           │  Main Bootloader (14 KB)│ ← UART XMODEM logic
0x00004000 ├─────────────────────────┤
           │  Application            │ ← NCP-UART-HW or Router firmware
           │  (~200 KB)              │
0x0003E000 ├─────────────────────────┤
           │  NVM3 Storage (36 KB)   │ ← Network keys, tokens
0x00040000 └─────────────────────────┘

Flashing the Bootloader¶

Warning: Bootloader firmware flashing always carries some risk. If the process is interrupted or fails, the device may become unresponsive and require a J-Link/SWD debugger to recover. Having a debugger available is strongly recommended before attempting any bootloader update.

Option 1: Flash via J-Link/SWD (Recommended)¶

The safest method. Flash the combined image (first stage + main stage):

commander flash firmware/bootloader-uart-xmodem-2.4.2-combined.s37 --device EFR32MG1B232F256GM48

Or flash stages separately:

# First stage (only if missing/corrupted)
commander flash firmware/first_stage.s37 --device EFR32MG1B232F256GM48

# Main stage with CRC
commander flash firmware/bootloader-uart-xmodem-2.4.2-crc.s37 --device EFR32MG1B232F256GM48

Option 2: Flash via `flash_efr32.sh` (Remote, Stage 2 only)¶

You can update the Stage 2 bootloader remotely if you already have a working bootloader installed.

Note: This only updates Stage 2. Stage 1 cannot be updated via UART.

From the repository root:

./flash_efr32.sh <GATEWAY_IP>
# Select [1] Bootloader

The script handles serialgateway restart, flashing, and the expected NoFirmwareError (the application slot is empty after a bootloader update). It then prompts you to select an application firmware (NCP, RCP, etc.) and flashes it immediately.

Creating Combined Images (Bootloader + Application)¶

To update both bootloader (stage 2) and application in one UART transfer:

commander gbl create upgrade.gbl \
    --app ncp-uart-hw.s37 \
    --bootloader bootloader-uart-xmodem-2.4.2-crc.s37

Note: This only updates the main bootloader (stage 2), not the first stage. First stage always requires SWD access.

patches/ Directory¶

File	Purpose
`bootloader-uart-xmodem.slcp`	Project config with components
`bootloader-uart-xmodem.slpb`	Post-build config (generates .s37, -crc.s37, -combined.s37, .gbl)
`btl_uart_driver_cfg.h`	UART pin configuration (USART0 PA0/PA1, no flow control)