# bench51 — an 8051 assembler, simulator & debugger A small, Keil µVision-style IDE for the Intel 8051, in two flavours: a TUI that runs in your terminal, and a desktop GUI (`bench51-gui`) laid out like µVision. Write assembly in the built-in editor, assemble it, inspect the listing and Intel HEX output, then run, pause and single-step the program while watching registers, SFRs, memory, ports, timers, interrupts and the serial port. Built in Rust with [ratatui](https://ratatui.rs) and [egui](https://github.com/emilk/egui). It is a learning tool, not a cycle-exact replacement for a vendor simulator. ![Debugging serial_hello.asm: source, registers, peripherals, IRAM and the UART console](docs/screenshots/debug_serial.png)
Editor with the assembled Keil-style listing Stopped at a breakpoint inside the timer 0 ISR, SFR view
Editor + assembled listing Breakpoint inside a timer ISR, SFR view
Assembler errors marked in the gutter and listed in the Errors tab Intel HEX output tab
Assembler errors in the gutter and Errors tab Intel HEX output
## Why this exists I had microcontroller practicals to get through, and the course expects you to use Keil µVision. Keil µVision doesn't run on Linux. Rather than fight with Wine or a Windows VM every lab session, I wrote my own: bench51 does the parts of µVision those practicals actually need (write the code, assemble it, look at the listing and HEX, step through it and watch the registers) right in the terminal. ----- ## Features - **Editor** with undo/redo, breakpoint and error markers in the gutter — or press Ctrl-G to edit in your own `$EDITOR` (vim, nvim, nano, …). - **Two-pass assembler** for the full 8051 instruction set (all 255 opcodes): - labels, expressions (`+ - * / MOD AND OR XOR NOT SHL SHR HIGH LOW`, `$`) - number formats `42`, `2Ah`, `0x2A`, `101010b`, `52o`, `'*'` - bit addressing (`P1.3`, `ACC.7`, `20h.0`) and all predefined SFR/bit names - directives `ORG DB DW DS END EQU SET BIT DATA IDATA XDATA CODE CSEG AT` - generic `JMP`/`CALL` (assembled as `LJMP`/`LCALL`) - Keil-style `.lst` listing with symbol table, Intel HEX output - **Simulator** - all instructions with correct flags (CY, AC, OV, P) and machine-cycle counts - 4 register banks, 256 bytes IRAM, SFRs, 64K code, 64K XRAM - ports P0–P3 with latch vs. pin semantics (read-modify-write reads the latch) - timers 0/1 in modes 0–3, gate and counter inputs - interrupts: INT0, T0, INT1, T1, serial; two priority levels; edge/level triggers - UART in modes 0–3 with baud rate timing from timer 1 - idle and power-down modes (PCON) - **Debugger**: run / pause, step into / over / out, run to cursor, breakpoints, changed-value highlighting, memory poke, adjustable speed. - **Open `.hex` files**: they're disassembled into editable source that re-assembles to the identical image. ## Usage ```bash cargo install --path . # installs the `bench51` binary cargo run --release -- examples/serial_hello.asm # open in the TUI cargo run --release # start with a template cargo run --release -- firmware.hex # disassemble & debug a HEX file # Headless assembly: writes prog.hex and prog.lst cargo run --release -- --assemble prog.asm cargo run --release -- --assemble prog.asm -o out.hex --lst out.lst ``` `--clock ` sets the oscillator frequency used for the elapsed-time display (default 11.0592). ## Desktop GUI `bench51-gui` is the same assembler and simulator behind a µVision-style window: menus and toolbar, a Project window, the editor with breakpoint gutter, Build Output, and in a debug session the Registers, Disassembly, Memory, Symbols, UART #1, Ports, Timers and Interrupts windows. Every window docks and tabs wherever you drag it; the edit and debug layouts are remembered separately, as in µVision. It follows a monochrome, dot-matrix design (Space Grotesk, Space Mono and Doto, bundled) in a dark and a light theme. ![Debug session in the GUI: registers, source with the PC, disassembly, memory and UART #1](docs/screenshots/gui_debug.png)
Editor and Keil-style build output Stopped at a breakpoint in a timer ISR, light theme
Editor + build output Breakpoint in a timer ISR, light theme
Ports, timers and interrupts windows docked side by side Assembler errors in the gutter and Build Output
Peripheral windows, rearranged Assembler errors
```bash cargo install --path crates/bench51-gui # installs `bench51-gui` cargo run --release -p bench51-gui # welcome screen cargo run --release -p bench51-gui -- examples/*.asm # open several files cargo run --release -p bench51-gui -- --theme light firmware.hex ``` `--theme system|dark|light` overrides the theme chosen in View → Theme, and `--clock ` the Xtal set in Project → Options for Target. The keys are µVision's, with the TUI's as aliases: | Key | Action | | --- | --- | | F7 | build target (also writes `.lst` and `.hex` next to a saved file) | | Ctrl-F5 / F4 | start / stop the debug session | | F5 | run / stop | | F11 / F10 | step into / step over | | Ctrl-F11 / F12 | step out | | Ctrl-F10 / F8 | run to the cursor line | | F9 / Ctrl-Shift-F9 | toggle breakpoint / remove all breakpoints | | F6 | reset the CPU | | Ctrl-N / Ctrl-O / Ctrl-S / Ctrl-W | new / open / save / close | | Ctrl-F | find | | F1 | all shortcuts | Click the gutter to toggle a breakpoint, double-click a byte in Memory to change it, click a pin in Ports to hold it low from outside, and click the bit chips in Registers, Timers and Interrupts to flip SFR bits. Files can be dropped onto the window. On Linux it runs on Wayland and X11 and uses the XDG desktop portal for file dialogs. To add it to your application launcher: ```bash install -Dm644 crates/bench51-gui/assets/bench51-gui.desktop ~/.local/share/applications/bench51-gui.desktop install -Dm644 crates/bench51-gui/assets/bench51-gui.svg ~/.local/share/icons/hicolor/scalable/apps/bench51-gui.svg ``` It also builds for Windows and macOS. On Debian or Ubuntu, first install the packages egui needs: `libxcb-render0-dev libxcb-shape0-dev libxcb-xfixes0-dev libxkbcommon-dev libssl-dev`. ## Keys | Key | Action | | --- | --- | | F1 | help | | F2 / Ctrl-S | save (assembling a saved file also writes `.lst` and `.hex` next to it) | | F3 / Ctrl-O | open `.asm` or `.hex` | | Ctrl-G | edit in `$EDITOR`; on save & exit the buffer reloads and reassembles | | F4 | switch Edit ⇄ Debug | | F7 | assemble, reset and load | | F5 | run / pause (assembles first if the source changed) | | F11 / F10 / F12 | step into / step over / step out | | F8 | run to cursor | | F9 | toggle breakpoint on the cursor line | | F6 | reset | | Ctrl-Q | quit | Edit mode: `Alt-1/2/3` switch between Listing, HEX and Errors; `Alt-↑/↓`, `Alt-PgUp/PgDn` scroll them. The editor uses Emacs-style keys (`Ctrl-U` undo, `Ctrl-R` redo, `Ctrl-Y` paste). Debug mode: `Tab` cycles focus between Source, Memory, Ports and Serial. Letter shortcuts work too, for terminals that swallow function keys: `r` run/pause, `s` step, `n` step over, `o` step out, `g` run to cursor, `b` breakpoint, `x` reset, `i`/`f`/`d`/`c` show IRAM/SFR/XRAM/CODE, `p` poke memory, `+`/`-` speed, `.` jump to PC, `Esc` pause / back to editor. - **Ports**: select a pin and press Space to pull it low from outside (a button press); the program sees the pin as `latch AND external level`. - **Serial**: type a line and press Enter to send it (followed by CR) to the 8051's receiver; everything the 8051 transmits appears above. ## Examples | File | Shows | | --- | --- | | `examples/blink.asm` | port toggling, delay loops, `ACALL`/`RET` | | `examples/timer_irq.asm` | timer 0 mode 1 interrupt | | `examples/serial_hello.asm` | UART setup, string output with `MOVC`, echo | | `examples/button_int0.asm` | edge-triggered INT0, idle mode | | `examples/bcd_add.asm` | `ADDC` and `DA A` with packed BCD | | `examples/lookup_movc.asm` | 7-segment table lookup | ## Notes and limitations - Indirect addressing reaches all 256 bytes of IRAM (8052-style upper 128). - Serial input has no 9th data bit; in modes 2/3 `RB8` reads 0. - No 8052 timer 2, external code memory or on-chip peripherals of derivatives. ## Development ```bash cargo test --workspace # assembler, CPU, peripheral, session and example-program tests cargo clippy --workspace --all-targets ``` Code layout: - `crates/bench51-core/`, shared by both front ends: `isa.rs` (opcode table), `asm/` (assembler, listing, Intel HEX), `sim/` (CPU, peripherals, disassembler), `session.rs` (build, run, step and breakpoints), `syntax.rs` (highlighting tokens), `files.rs` (HEX loading) - `src/` is the `bench51` TUI (ratatui). - `crates/bench51-gui/` is the `bench51-gui` desktop app (egui).