SiLabs 8051 Debug
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.
