libc8

c8 (CHIP-8 Interpreter)

This is a fully functional CHIP-8 and SCHIP interpreter with an integrated debug mode, utilizing libc8 with SDL2.

Usage

c8 [-dvV] [-c clockspeed] [-f small,big] [-p file] [-P colors] [-q quirks] file

• -c sets the number of instructions to be executed per second (default: 1000).
• -d enables debug mode. This can be used to add breakpoints, display the current memory, and step through instructions individually.
• -f loads the specified comma-separated fonts. Big font is optional.
• -p loads a color palette from a file containing two newline-separated 24-bit hex codes.
• -P sets the color palette from a string containing two comma-separated 24-bit hex codes.
• -q sets the quirks to enable from string with non-separated quirk identifiers
• -v enables verbose mode. This will print each instruction that is executed.
• -V prints the version number.

Keyboard layout is the following:

  Key       CHIP-8 keycode
1 2 3 4        1 2 3 C
q w e r  ==>   4 5 6 D
a s d f        7 8 9 E
z x c v        A 0 B F

Fonts

Same as Octo.

Small fonts:

• octo
• vip
• dream6800
• eti660
• fish

Big fonts:

• octo
• schip
• fish

Quirks

The following quirks are available:

• b: After AND, OR, and XOR: Clear VF.
• d: For DRW: Clip sprites at edge of display.
• j: For JP V0, nnn: Jump to nnn + V[(nnn>>8)&0xF] instead.
• l: After LD [I], Vx and LD Vx, [I]: Set I to address I + x + 1.
• s: Before SHL Vx, Vy and SHR Vx, Vy: Shift Vx in place, ignore Vy.

Debug mode

Debug mode can be enabled via the -d command-line argument or by pressing P at any time during execution. It can also be disabled at any time by pressing M.

The following commands are supported in debug mode:

• break [ADDRESS]: Add breakpoint to PC or ADDRESS, if given.
• rmbreak [ADDRESS]: Remove breakpoint at PC or ADDRESS, if given and exists.
• continue: Exit debug mode until next breakpoint or until execution is complete.
• help: Print a help string.
• load PATH: Load program state from PATH.
• loadflags PATH: Load flag registers from PATH.
• next: Step to the next instruction.
• print [ATTRIBUTE]: Print current value of the given attribute.
• quit: Terminate the program.
• save PATH: Save program state to PATH.
• saveflags PATH: Save flag registers to PATH.
• set ATTRIBUTE VALUE: Set the given attribute to the given value.

Attributes:

• PC: Program counter
• SP: Stack pointer
• DT: Delay timer
• ST: Sound timer
• I: I value
• K: Register to store next keypress
• V[x]: All V register values or value of Vx, if given
• R[x]: All R (flag) register values or value of Rx, if given
• bfont: Big font name
• sfont: Small font name
• stack: All stack values
• bg: Background color
• fg: Foreground color
• $[address]: Value at given address

If no argument is given to print, it will print all of the above attributes except for address values.

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