Pico-Code

The Pico-Code is the blueprint for the GC's hardware. Even though each of the 16 possible microcode instructions theoretically takes the same amount of time (one clock-tick), it conceptually executes a unique block of pico-code. The pico-code hardware consists of an (almost) infinitely long tape of ones and zeros, plus a set of 16 registers and a 16-bit program counter (PC). Each register is 65,536 bits long. Register 0 is the accumulator (ACC). Register 1 is the data register (DAT). All pico-code instructions are stored in a buffer of size 32 KB. Each pico-code instruction is a multiple of 4 bits long. See Appendix A for the contents of the pico-code buffer.

 

Pico-Code Instructions

Name	Op Code	Length	Description
DTX	0000	20	DAT = X; X is a signed 16-bit value
DTA	0001	20	DAT = 2 raised to the X-th power; X is a 16-bit value
DSH	0010	4	DAT = DAT >> 1
ACD	0011	4	ACC = ACC + DAT
ACZ	0100	4	ACC = 0
MOV	1000	12	REG X = REG Y; X,Y are 4-bit values
JMP	1001	20	PC = X; X is a 16-bit value
BRZ	1010	20	PC = X (if ACC = 0)
BRN	1011	20	PC = X (if ACC < 0)
JIN	1100	8	PC = REG Y; Y is a 4-bit value
TRD	1101	8	DAT[0] = Tape[REG Y]  (read a bit from the tape)
TWR	1110	8	Tape[REG Y] = DAT[0]  (write a bit to the tape)
RET	1111	4	Return or Halt