Calico LC3

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Calico LC3 is an assembly language based on the Little Computer by Patt and Patel.


Calico LC3 is an implementation of Patt and Patel's LC3 assembly language. The language is written in Calico Python, but appears as a full language in Calico.

In Calico, you need to first enable the LC3 language before using it:

  1. start Calico
  2. under menu -> Calico -> Languages
  3. make sure that "LC3" is checked
  4. Create a new LC3 script, or examine one of the Examples
  5. (Enable "Spreadsheet", too if you want to use it to display memory)

Special features:

  • Tracing, breakpoints, integrated IDE
  • syntax color highlighting
  • Right-click on errors takes you to line of code
  • Assembler and interpreter
  • Counts instructions executed
  • Counts machine cycles executed, estimates milliseconds to run
  • Error checking and useful error messages
  • menu -> View -> Tabs -> Locals - shows registers
  1. Shows memory as Calico Spreadsheet

Source Materials:

Special Interactive Directives

Enter these commands in the Calico Shell entry area:

Interactive Directives: 
 .help                           - shows this info
 .show memory                    - display memory as a Spreadsheet
 .assemble                       - assemble the first .asm file in Calico
 .step                           - execute the next instruction, increment PC
 .reset                          - reset LC3 to start state") 
 .raw [start [stop]]             - list meory in hex
 .list                           - list program from memory
 .dump [start [stop]]            - dump memory as program
 .regs                           - show registers
 .set pc HEXVALUE                - set PC
 .set memory HEXLOCATION HEXVALUE- set memory
 .set reg VALUE HEXVALUE         - set register
 .get pc                         - get PC
 .get memory HEXLOCATION         - get memory
 .get reg VALUE                  - get register


ADD DR, SR1, SR2       ; Addition
ADD DR, SR1, imm5      ; Addition with Immediate
AND DR, SR1, SR2       ; Bit-wise AND
AND DR, SR1, imm5      ; Bit-wise AND with Immediate
BRx, label (where x = {n,z,p,zp,np,nz,nzp}) ; Branch
JMP BaseR              ; Jump
JSR label              ; Jump to Subroutine
JSRR BaseR             ; Jump to Subroutine in Register
LD DR, label           ; Load PC-Relative
LDI DR, label          ; Load Indirect
LDR DR, BaseR, offset6 ; Load Base+Offset
LEA, DR, label         ; Load Effective Address
NOT DR, SR             ; Bit-wise Complement
RET                    ; Return from Subroutine
RTI                    ; Return from Interrupt
ST SR, label           ; Store PC-Relative
STI, SR, label         ; Store Indirect
STR SR, BaseR, offset6 ; Store Base+Offset
TRAP immediate-vector  ; System Call

Also added experimental SHIFT:

SHIFT DestR, SR, immed6 ; shift source register (SR) by immed6 
                        ; (positive, left; negative right) and 
                        ; store in destination register (DestR)


Here is a basic Hello World assembly program.

;; helloworld.asm
.ORIG x3000
HELLO .STRINGZ "Hello, World!\n"

There are more examples in menu -> File -> Examples -> LC3.

Future Possibilities

  1. integrate with other languages
  2. create real code that could be executed on computer (maybe .NET/Mono VM code?)
  3. load/run binary-text files and obj files
  4. show dissassembled code