What SWD is, how debug probes work, which ones to choose, and how production teams scale from one probe to many. Written by embedded engineers, for embedded engineers.
What is SWD? Compare Debug ProbesPractical knowledge for every stage — from your first SWD connection to a 7-channel production test farm.
Serial Wire Debug explained from the ground up. The 2-wire protocol ARM designed to replace JTAG for Cortex-M debugging. Signals, timing, how it works.
Read the guide → →SEGGER J-Link, ST-Link, DAPLink, CMSIS-DAP, Black Magic Probe — what they cost, what they do, and which one fits your workflow.
See the comparison → →When you need to flash and test more than one board at a time. Gang programmers, J-Link farms, and the gap between programming and testing.
Explore multi-target → →If you've ever searched for "how to connect an SWD probe" or "which debug probe should I buy", you've probably found a mix of forum posts from 2014, vendor marketing that assumes you already know everything, and Stack Overflow answers that contradict each other.
We're building this as the reference we wish existed — clear, practical, vendor-neutral information about SWD debugging and embedded test infrastructure. Whether you're connecting your first probe to an STM32 or scaling to production test across dozens of targets.
We're also building a product: a multi-channel SWD test probe designed for parallel production testing. It's not ready yet — but if that's the problem you're solving, register for early access and we'll let you know when it ships.
SWD uses 2 wires (SWDIO + SWCLK) instead of JTAG's 4-5. Same debug access, fewer pins, designed specifically for ARM Cortex-M. Most modern Cortex-M chips support both.
Yes. SWD can flash firmware at full speed, verify the image, and optionally lock the chip. Most production programmers use SWD as the transport protocol.
For hobby/learning: a £3 ST-Link clone works. For professional work: reliability, speed, and support matter — J-Link and CMSIS-DAP probes are the standard. For production: you need something designed for it.
Depends on the probe and target. A J-Link Plus with SWD hits ~2-3 MB/s on most Cortex-M targets. Budget probes: 100-500 KB/s. USB HS probes with DMA: up to 15+ MB/s.
The SWD connection itself doesn't carry power. Some probes (J-Link, ST-Link) have a VCC pin that can supply 5V/3.3V at ~300 mA for small targets. For production, use a dedicated power supply.
Use pyOCD, OpenOCD, or probe-rs from the command line. All support scripting, CI/CD integration, and can flash + verify + reset in a single command. SEGGER has J-Flash for batch operations.
We're developing a 7-channel SWD test probe with per-channel logic analyser, UART capture, and current measurement. Register to be notified when it ships.
Register for Early Access