Debug - Lager

Control debugger operations for embedded development including flashing, GDB server management, memory access, and RTT logging.

Syntax

lager debug [OPTIONS] [NET_NAME] COMMAND [ARGS]...

Global Options

Option	Description
`--box TEXT`	Lagerbox name or IP address
`--help`	Show help message and exit

Commands

Command	Description
`gdbserver`	Start JLinkGDBServer for debugging
`disconnect`	Stop JLinkGDBServer
`flash`	Flash firmware to target
`reset`	Reset target device
`erase`	Erase all flash memory
`memrd`	Read memory from target
`status`	Show debug net status
`health`	Check debug service health

Command Reference

`gdbserver`

Start JLinkGDBServer for remote debugging. This is the primary command to establish a debug connection.

lager debug [NET_NAME] gdbserver [OPTIONS]

Options:

--box TEXT - Lagerbox name or IP
--force / --no-force - Force new connection (default: reuse existing)
--halt / --no-halt - Halt device when connecting (default: no-halt)
--speed KHZ - SWD/JTAG speed in kHz (e.g., 100, 4000) or “adaptive”
--quiet - Suppress informational messages
--json - Output results in JSON format
--rtt - Automatically stream RTT logs after starting GDB server
--rtt-reset - Reset device then stream RTT (captures boot sequence)
--reset - Reset device after starting GDB server
--gdb-port PORT - Override the auto-allocated GDB server port. By default the box picks a port based on the probe’s slot (2331 for the first probe, 2334 for the second, etc.); pass this only if you need a specific port, and avoid it on multi-probe boxes.
--rtt-search-addr HEX - RAM start address for the RTT control block search (hex, e.g., 0x20020000)
--rtt-search-size HEX - Size of the RAM region to search for the RTT control block (hex, e.g., 0x4000)
--rtt-chunk-size HEX - Read chunk size for the RTT search (hex, e.g., 0x1000)

Examples:

# Start GDB server on default debug net
lager debug gdbserver --box my-lager-box

# Start GDB server on specific net with halt
lager debug debug1 gdbserver --box my-lager-box --halt

# Start GDB server and stream RTT logs
lager debug gdbserver --box my-lager-box --rtt

# Capture boot sequence via RTT
lager debug gdbserver --box my-lager-box --rtt-reset

# Use custom speed and port
lager debug gdbserver --box my-lager-box --speed 4000 --gdb-port 3333

Connecting with GDB:

# After starting gdbserver, connect with:
arm-none-eabi-gdb firmware.elf -ex 'target remote <BOX_IP>:2331'

`disconnect`

Stop JLinkGDBServer and free debug resources.

lager debug [NET_NAME] disconnect [OPTIONS]

Options:

--box TEXT - Lagerbox name or IP
--keep-server - Keep JLinkGDBServer running for external connections

Examples:

# Stop GDB server completely
lager debug disconnect --box my-lager-box

# Disconnect but keep server running
lager debug disconnect --box my-lager-box --keep-server

`flash`

Flash firmware to target. Supports Intel HEX, ELF, and binary file formats.

lager debug [NET_NAME] flash [OPTIONS]

Options:

--box TEXT - Lagerbox name or IP
--hex FILE - Path to Intel HEX file
--elf FILE - Path to ELF executable
--bin ADDRESS FILE - Path to binary file with load address
--verbose - Show detailed J-Link output
--force-reconnect - Force clean reconnect before flash
--no-erase - Skip the erase step (by default flash erases before programming for a clean state)
--halt / --no-halt - Halt device after flashing (default: no-halt)

flash erases before programming by default, so no flag is needed for a clean state (this is what RTT initialization wants). Pass --no-erase only when you intentionally want to preserve existing flash contents. The older --erase flag is now a no-op kept for backward compatibility.

Examples:

# Flash Intel HEX file
lager debug flash --hex build/firmware.hex --box my-lager-box

# Flash ELF file
lager debug flash --elf build/firmware.elf --box my-lager-box

# Flash binary with base address
lager debug flash --bin 0x08000000 build/firmware.bin --box my-lager-box

# Flash while preserving existing flash contents (skip the default erase)
lager debug flash --hex build/firmware.hex --no-erase --box my-lager-box

# Flash and halt for debugging
lager debug flash --elf build/firmware.elf --halt --box my-lager-box

# Verbose output for troubleshooting
lager debug flash --hex build/firmware.hex --verbose --box my-lager-box

`reset`

Reset the target device.

lager debug [NET_NAME] reset [OPTIONS]

Options:

--box TEXT - Lagerbox name or IP
--halt / --no-halt - Halt after reset (default: no-halt)
--force-reconnect - Force clean reconnect before reset

Examples:

# Reset and run
lager debug reset --box my-lager-box

# Reset and halt (for debugging)
lager debug reset --halt --box my-lager-box

# Force clean state before reset
lager debug reset --force-reconnect --box my-lager-box

`erase`

Erase all flash memory on target. This is a destructive operation.

lager debug [NET_NAME] erase [OPTIONS]

Options:

--box TEXT - Lagerbox name or IP
--speed KHZ - SWD/JTAG speed in kHz (default: 4000)
--yes - Skip confirmation prompt
--quiet - Suppress warning messages
--json - Output results in JSON format
--halt / --no-halt - Halt after erase (default: no-halt)

Examples:

# Erase with confirmation prompt
lager debug erase --box my-lager-box

# Erase without confirmation
lager debug erase --box my-lager-box --yes

# Erase and halt afterward
lager debug erase --box my-lager-box --yes --halt

`memrd`

Read memory from the target device.

lager debug [NET_NAME] memrd START_ADDR LENGTH [OPTIONS]

Arguments:

START_ADDR - Starting memory address (e.g., 0x20000000)
LENGTH - Number of bytes to read

Options:

--box TEXT - Lagerbox name or IP
--json - Output results in JSON format
--halt / --no-halt - Halt device during read (default: no-halt). --no-halt overrides the auto-halt for DA1469x QSPI XIP
--no-reset - DA1469x only. Skip the reset+halt the box performs before the read. A running DA1469x has SWD disabled, so without the reset the read fails — use this only on a blank/awake part to avoid rebooting it

Examples:

# Read 16 bytes of SRAM
lager debug memrd 0x20000000 16 --box my-lager-box

# Read with device halted (more reliable)
lager debug memrd 0x20000000 64 --halt --box my-lager-box

# Output as JSON
lager debug memrd 0x08000000 32 --json --box my-lager-box

# DA1469x: read a blank/awake part without rebooting it
lager debug memrd 0x20000000 16 --no-reset --box my-lager-box

Output:

0x20000000:	0x00	0x01	0x02	0x03	0x04	0x05	0x06	0x07
0x20000008:	0x08	0x09	0x0a	0x0b	0x0c	0x0d	0x0e	0x0f

`status`

Show debug net status and configuration information.

lager debug [NET_NAME] status [OPTIONS]

Options:

--box TEXT - Lagerbox name or IP

Examples:

lager debug status --box my-lager-box
lager debug debug1 status --box my-lager-box

Output:

Debug Net Information:
  Name: debug1
  Device Type: STM32F407VG
  Architecture: ARM Cortex-M4
  Probe: J-Link
  Connected: True

`health`

Check debug service health and resource usage.

lager debug [NET_NAME] health [OPTIONS]

Options:

--box TEXT - Lagerbox name or IP
--verbose - Show detailed health information

Examples:

# Basic health check
lager debug health --box my-lager-box

# Detailed health information
lager debug health --box my-lager-box --verbose

Output (verbose):

Debug Service Health:
  Status: healthy
  Version: 1.2.0
  Uptime: 2.5 days (216000s)
  J-Link Running: True
  J-Link PID: 12345
  GDB Controllers Cached: 1
  Active Connections: 1

Listing Debug Nets

When invoked with only --box and no subcommand, lists all debug nets on the Lager Box:

lager debug --box my-lager-box

Output:

Name    Net Type  Instrument  Channel      Address
debug1  debug     J-Link      STM32F407VG  USB::001::002
debug2  debug     CMSIS-DAP   nRF52840     USB::001::003

RTT (Real-Time Transfer) Logging

RTT provides low-latency logging over the debug probe. Use the --rtt or --rtt-reset flags with gdbserver:

# Stream RTT after connecting
lager debug gdbserver --box my-lager-box --rtt

# Reset device and capture boot messages
lager debug gdbserver --box my-lager-box --rtt-reset

# Pipe to defmt-print for formatted output
lager debug gdbserver --box my-lager-box --rtt 2>/dev/null | defmt-print -e firmware.elf

Decoding defmt logs

Most Rust (and much C) firmware logs via defmt, a compressed binary format. Raw RTT bytes from defmt firmware are not human-readable — they must be decoded by defmt-print using the exact ELF that is flashed on the target.

# Flash the build under test, then stream + decode a bounded window
lager debug SWD flash --elf build/app.elf --box my-lager-box
timeout 15 lager debug SWD gdbserver --box my-lager-box --rtt-reset 2>/dev/null \
  | defmt-print -e build/app.elf

Two things to watch:

Redirect stderr. The RTT payload is written to stdout; status messages (JLinkGDBServer started!, etc.) go to stderr. Pipe stdout only — append 2>/dev/null (or 2>debug.log) so status lines never corrupt defmt-print’s input.
The stream never ends. --rtt runs until the process is killed. In scripts or non-interactive sessions, wrap it in timeout <seconds> to capture a fixed window; when the lager process is killed the pipe closes and defmt-print exits on EOF.

Install defmt-print with cargo install defmt-print on the machine where you run the pipe (the same machine that holds the .elf).

Typical Workflows

Development Cycle

# Flash and debug
lager debug flash --elf build/app.elf --box my-lager-box
lager debug gdbserver --box my-lager-box --halt

# In another terminal, connect GDB
arm-none-eabi-gdb build/app.elf -ex 'target remote <BOX_IP>:2331'

RTT Debugging

# Flash for a clean RTT state (erase happens by default)
lager debug flash --elf build/app.elf --box my-lager-box

# Start GDB server and stream RTT with boot capture
lager debug gdbserver --box my-lager-box --rtt-reset

Memory Inspection

# Halt device and read memory
lager debug gdbserver --box my-lager-box --halt
lager debug memrd 0x20000000 256 --box my-lager-box

Clean Up

# Stop debug session
lager debug disconnect --box my-lager-box

# Full chip erase before new project
lager debug erase --box my-lager-box --yes

JLinkScript Support

JLinkScript files allow you to customize J-Link debug probe behavior for specific hardware configurations. They can handle custom reset sequences, clock initialization, pin configurations, and other device-specific operations that the standard J-Link connection flow does not cover.

Configuring JLinkScript

There are three ways to attach a J-Link script to a debug net: 1. During net creation:

lager nets add debug1 debug STM32F407VG USB::001::002 \
  --jlink-script ./my_device.JLinkScript --box my-lager-box

2. On an existing net:

lager nets set-script debug1 ./my_device.JLinkScript --box my-lager-box

3. Per-project in .lager config:

{
  "DEBUG": {
    "debug1": "./scripts/my_device.JLinkScript"
  }
}

Script Priority

When both a net-level script (stored on the box via set-script) and a project-level script (in .lager config) exist, the project-level script takes priority. This allows you to override the box-stored script for specific projects.

Managing Scripts

# View attached script
lager nets show-script debug1 --box my-lager-box

# Save script to local file
lager nets show-script debug1 --box my-lager-box > script.JLinkScript

# Remove script from net
lager nets remove-script debug1 --box my-lager-box

Once attached, the script is used automatically for all debug operations (connect, flash, erase, reset) without any additional flags.

Supported Debug Probes

Probe	Backend	Notes
J-Link	JLinkGDBServer	Full feature support, RTT, JLinkScript
J-Link Plus	JLinkGDBServer	Full feature support, RTT, JLinkScript
CMSIS-DAP	pyOCD	Open source, wide device support
ST-Link	pyOCD	STM32 devices
Flasher ARM	JLinkGDBServer	Production programming

Supported Device Families

Lager supports 70+ ARM Cortex-M device families with automatic architecture detection. The device type is specified as the channel when creating a debug net (e.g., STM32F407VG, nRF52840).

Cortex-M0/M0+ (ARMv6-M)

Family	Manufacturer
RP2040	Raspberry Pi
nRF51	Nordic Semiconductor
STM32C0	STMicroelectronics
STM32F0	STMicroelectronics
STM32G0	STMicroelectronics
STM32L0	STMicroelectronics
LPC8xx, LPC11xx	NXP
ATSAMD, ATSAML, ATSAMC	Microchip/Atmel
EFM32 Zero Gecko	Silicon Labs

Cortex-M3 (ARMv7-M)

Family	Manufacturer
STM32F1	STMicroelectronics
STM32F2	STMicroelectronics
STM32L1	STMicroelectronics
LPC13xx, LPC17xx, LPC18xx	NXP
LM3, LM4F (Stellaris/Tiva-C)	Texas Instruments
EFM32 Giant/Leopard/Wonder Gecko	Silicon Labs

Cortex-M4/M7 (ARMv7E-M)

Family	Manufacturer
nRF52	Nordic Semiconductor
STM32F3	STMicroelectronics
STM32F4	STMicroelectronics
STM32F7	STMicroelectronics
STM32G4	STMicroelectronics
STM32H7	STMicroelectronics
STM32L4	STMicroelectronics
STM32WB	STMicroelectronics
STM32WL	STMicroelectronics
MKxxxx (Kinetis K)	NXP
LPC4xxx, LPC54xxx	NXP
MIMXRT (i.MX RT)	NXP
TM4C	Texas Instruments
MSP432	Texas Instruments
CC26xx, CC13xx	Texas Instruments
ATSAM4, ATSAME, ATSAMS, ATSAMV	Microchip/Atmel
EFM32, EFR32	Silicon Labs
CY, PSoC	Infineon
DA145x, DA146x, DA148x	Dialog Semiconductor

Cortex-M23 (ARMv8-M Base)

Family	Manufacturer
LPC55S0x	NXP

Cortex-M33/M55 (ARMv8-M Main)

Family	Manufacturer
nRF53	Nordic Semiconductor
nRF91	Nordic Semiconductor
STM32L5	STMicroelectronics
STM32U5	STMicroelectronics
STM32H5	STMicroelectronics
STM32WBA	STMicroelectronics
LPC55S	NXP
R7FA (Renesas RA)	Renesas

Devices not in the table above default to Cortex-M4 (ARMv7E-M) architecture. If your device is not detected correctly, specify the full device part number (e.g., STM32F407VG rather than just STM32F4) when creating the debug net.

Notes

Debug nets are created with lager nets add <name> debug <device_type> <address>
The system auto-connects when needed for commands like flash and reset
flash erases before programming by default, giving a clean state for RTT initialization (use --no-erase to opt out)
RTT streaming requires the device to have RTT support in firmware
Memory reads are more reliable with --halt to pause the CPU
Use lager debug health --verbose to diagnose connection issues
JLinkScript files are base64-encoded for storage and decoded automatically on the box

​Syntax

​Global Options

​Commands

​Command Reference

​gdbserver

​disconnect

​flash

​reset

​erase

​memrd

​status

​health

​Listing Debug Nets

​RTT (Real-Time Transfer) Logging

​Decoding defmt logs

​Typical Workflows

​Development Cycle

​RTT Debugging

​Memory Inspection

​Clean Up

​JLinkScript Support

​Configuring JLinkScript

​Script Priority

​Managing Scripts

​Supported Debug Probes

​Supported Device Families

​Cortex-M0/M0+ (ARMv6-M)

​Cortex-M3 (ARMv7-M)

​Cortex-M4/M7 (ARMv7E-M)

​Cortex-M23 (ARMv8-M Base)

​Cortex-M33/M55 (ARMv8-M Main)

​Notes

​See Also

Syntax

Global Options

Commands

Command Reference

`gdbserver`

`disconnect`

`flash`

`reset`

`erase`

`memrd`

`status`

`health`

Listing Debug Nets

RTT (Real-Time Transfer) Logging

Decoding defmt logs

Typical Workflows

Development Cycle

RTT Debugging

Memory Inspection

Clean Up

JLinkScript Support

Configuring JLinkScript

Script Priority

Managing Scripts

Supported Debug Probes

Supported Device Families

Cortex-M0/M0+ (ARMv6-M)

Cortex-M3 (ARMv7-M)

Cortex-M4/M7 (ARMv7E-M)

Cortex-M23 (ARMv8-M Base)

Cortex-M33/M55 (ARMv8-M Main)

Notes

See Also