Debug80 Docs

Debug80 Book 1 — Getting started06

Inspecting a running program ​

VS Code provides the Variables, Watch and Call Stack panels. Debug80 adds Registers, Memory, Machine and Displays sections for the Z80 and the board.

Symbols and Constants in Variables ​

The Variables panel shows source-map-backed Symbols and Constants after a successful build. Constants show their assembled value. Memory-backed symbols show their address, current bytes, readable ASCII where there is any, and source location.

Symbols and Constants in the Variables panel

Watch expressions ​

The Watch panel evaluates Z80 expressions while execution is paused, so a small set of facts can stay on screen while you step. A symbol on its own evaluates to its address or constant value, and square brackets read a byte from memory. Comparisons use =, !=, <>, <, <=, > and >=.

Appendix A lists the full expression language, which Watch shares with conditional breakpoints.

Call Stack naming ​

The Call Stack view names the current Z80 frame from the nearest known symbol in the source map. ScanHello+3 means the PC is three bytes past the ScanHello label. Frames below it come from the monitor and library source.

Registers ​

Debug80 keeps the CPU registers in their own Registers section: the pairs BC, DE, HL, AF, IX, IY, the shadow set BC', DE', HL', AF', and PC and SP. The interrupt and refresh registers I and R are read-only.

The Registers section

Each debugger step advances PC to the next instruction.

These fields are editable while the program is paused. Selecting a field and typing a value prepares the edit; Enter commits it and Escape reverts it. The flag strings beside the pairs work the same way, allowing a branch to be tested with a flag set or clear.

Memory ​

The Memory section is four independent views, labelled A to D, which default to following PC, SP, HL and DE.

The four memory views, each with its own anchor

Each view has an anchor box that accepts three kinds of value:

  • a register name, so the view follows that register as it changes
  • a symbol from the source map, such as SevenSegHello
  • an absolute address: plain hex, 0x-prefixed, or d: followed by a decimal number

Beside the anchor, Debug80 shows the resolved address and the nearest symbol with an offset.

A view shows sixteen bytes either side of its anchor, row-aligned, with an ASCII gutter and the anchor byte highlighted. Rows hold sixteen bytes when there is room and eight when the sidebar is narrow. While the program is paused the views refresh about twice a second.

Editing memory ​

Every byte in a memory view is an editable field. Selecting one and typing a value prepares the edit; Enter commits it and Escape reverts it. Editing works only while the program is paused.

Writing to read-only memory

Bytes in ROM are marked read-only, and Unlock read-only memory in the section makes them writable. Until you tick it, an edited byte snaps back and Debug80 reports:

text
Read-only memory locked

The Machine section ​

The Machine section shows the front-panel parts of the TEC-1G: the 20x4 LCD, the six seven-segment digits and the hex keypad.

Displays ​

The Displays section holds the rest of the TEC-1G's output: the speed and mute controls, the status and memory-bank indicators, the 128x64 GLCD and the 8x8 RGB LED matrix.

Debug80 renders the RGB matrix with duty-cycle brightness, so pixel brightness indicates the program's timing as well as its output.

The Displays section

SLOW and FAST switch the emulated clock. MUTED and SOUND control the speaker, which starts muted; audio unlocks on your first click or key press in the panel.

Keyboard focus ​

The hex keypad, matrix keyboard and joystick can compete for physical key input. Clicking a surface gives it keyboard focus; the on-screen controls continue to work regardless of that focus.

Video, input and serial explains the input priority, focus indicator, release command and macOS key handling.