GitHub: https://github.com/KMIMusic/C8051_dap_server
Author: Eric Bateman — Muse Kinetics
License: MIT

VSCode debug adapter for Silicon Laboratories C8051F-series MCUs via the Silicon Labs 8-Bit USB Debug Adapter.

Drives the SiC8051F.dll AGDI library that ships with Keil µVision, exposing it as a standard Debug Adapter Protocol server. Press F5 to build, flash, and debug directly from VSCode.

Requirements

Windows 10 / 11
Keil µVision installed (C51 toolchain) — required for UV4.exe (build) and the two adapter DLLs (SiC8051F.dll, USBHID.dll) which are copied automatically on first use
Silicon Laboratories 8-Bit USB Debug Adapter connected to the target board
Target: C8051F-series MCU (tested: C8051F380 / EFM8UB20F64G)

First-time setup

Install this extension from the VSIX: Extensions panel (Ctrl+Shift+X) → ... menu → Install from VSIX…
On the first debug session the extension will:
- Locate your Keil installation automatically via the Windows registry
- Copy SiC8051F.dll and USBHID.dll from your Keil folder into the extension's bin\
- Start the DAP server in the background
If Keil is not at a standard path, set it in settings:
```
// .vscode/settings.json
{ "silabs8051.keilPath": "C:\\path\\to\\Keil_v5" }
```

Per-project setup

Open (or create) .vscode/launch.json in your firmware project, click Add Configuration… at the bottom-right, and choose one of:

Snippet	What it does
SiLabs 8051: Flash + Debug	Build → flash → open a live debug session
SiLabs 8051: Flash Only	Build → erase → program → verify (no debug session)
SiLabs 8051: Flash Only (no erase)	Build → program → verify, skipping the erase pass

Then replace YourProject.uvproj with the path to your Keil µVision project file.

Usage

Press F5 (or the play button in the Run & Debug panel) and select a configuration. The extension handles everything automatically:

Starts the DAP server if not already running
Invokes UV4.exe -b to build the project (when buildBeforeDebug: true)
Invokes UV4.exe -f to flash the target (flash-only configs)
Connects VSCode to the DAP server and begins the debug session

Launch configuration reference

Field	Default	Description
`uvprojFile`	(auto-detect)	Path to the Keil project file (`.uvproj` / `.uvprojx`). Auto-detected if omitted. Supports `${workspaceFolder}` and `${workspaceFolder:Name}`.
`program`	(from uvproj)	Path to the Intel HEX file. Derived from the project file if omitted.
`buildBeforeDebug`	`false`	`true` → run `UV4.exe -b` before launching.
`buildTarget`	(from .uvopt)	µVision target name passed as `-t <name>` to UV4.exe. If omitted, UV4 uses whichever target was last active in the project.
`noDebug`	`false`	`true` → flash-only mode, no debug session.
`noErase`	`false`	`true` → skip erase pass (program + verify only, faster).

Debug features

Feature	Notes
Breakpoints	Source-line and instruction breakpoints; max 4 active (hardware limit)
Step over / into / out	Source-level and instruction granularity
Pause	Halts a running target
Variables / Locals	Local variables from debug info
Registers	R0–R7, ACC, B, SP, DPTR, PSW, PC — Registers panel in Debug sidebar
Edit values	Right-click any variable or watch → Set Value to write to hardware
Watch expressions	SFR names, register names, hex addresses (`ACC`, `0x20`, …)
Memory panels	DATA / XDATA / IDATA / CODE panels in Debug sidebar, auto-refresh on halt
Read/write memory	`DATA:0xNN`, `XDATA:0xNNNN`, `CODE:0xNNNN`, `IDATA:0xNN` in Watch
Disassembly	Right-click in editor → Open Disassembly View while paused

Note: The built-in VS Code Memory Inspector is not supported. Use the DATA / XDATA / IDATA / CODE sidebar panels instead.

Troubleshooting

"Keil installation not found" → Set silabs8051.keilPath in VS Code settings to your Keil root folder.

"Failed to connect to DAP server" / ECONNREFUSED → The DAP server failed to start. Check that dap_server.exe is present in the extension's bin\ folder and that the DLLs were copied successfully.

"Target not connected" / INITFEATURES returns 1 → Check that the USB Debug Adapter is plugged in and the debug header is connected.

Build output not appearing → Open the SiLabs 8051 Build output channel (View → Output).

Port 4711 already in use → Kill any existing dap_server.exe process via Task Manager, then retry.