ROSE-8 v0.2.2
ISA by Jordan Rose
https://belkadan.com/source/ROSE-8/

* Eight completely symmetric general-purpose registers (r0-7) - initially 0
* pc (16-bit address) - initially 0
* it (accumulator) - initially 0
* code (segment) - initially 1
* data1 (segment) - initially 255
* data2 (segment) - initially 254

7654_3210

0000_0000 STOP halts execution, like an invalid instruction
     0001 NOPE "no operation" (with a more fun mnemonic)
     0010 PRNT print it (for debugging or toy programs)
     0011 WAIT spin or sleep until data1[it] > 0, then decrement data1[it] (for MMIO)
     010x
     0110 CABA call absolute code[it], it <- return addr, code <- return segment
     0111 COFA call offset pc ± it, it <- return offset (-it + 1)

0000_1ooo ALU1 it <- {zero, lsl1, lsr1, asr1, incr, decr, comp, negt} it

0001_0000 GET1 it <- data1
     0001 GET2 it <- data2
     0010 GETC it <- code
     0011      (reserved for another special register)
     01xx
     1000 SET1 data1 <- it
     1001 SET2 data2 <- it
     1010 SETC code  <- it
     1011      (reserved for another special register)
     11xx

0010_0aaa GETR it <- it
   0_1aaa SETR ra <- it
   1_0aaa SWAP ra <- it, it <- ra
   1_1aaa ISLT "is less than", for testing overflow / carries: it <- (it < ra) ? 1 : 0

01oo_oaaa ALUR it <- it {addr, subr, andr, iorr, xorr, lslr, lsrr, asrr} ra

1000_0aaa LD1R it <- data1[ra]
  00_1aaa ST1R data1[ra] <- it
  01_0aaa LD1U it <- data1[ra], then ra += 1
  01_1aaa ST1U data1[ra] <- it, then ra += 1
  10_0aaa LD2R it <- data2[ra]
  10_1aaa ST2R data2[ra] <- it
  11_0aaa LD2U it <- data2[ra], then ra += 1
  11_1aaa ST2U data2[ra] <- it, then ra += 1

110x_xaaa               (reserved w/ register)

1110_0aaa LD2D ra -= 1, then it <- data2[ra]
1110_1aaa ST2D ra -= 1, then data2[ra] <- it

1111_00oo iiiiiiii ALUI it <- it {andi, iori, xori, (see below)} i
     0011 0iiiiiii ADDI it <- it + i
     0011 10oooiii BITI it <- it {roli, lsli, lsri, asri, (clri), (insi), (togi), exti} i
     0011 11iiiiii ADDI it <- it + (whole field, thus allowing many negative numbers)
     0100 iiiiiiii BEZI branch pc ± i if it == 0
     0101 iiiiiiii JOFI jump offset to pc ± i
     0110 iiiiiiii CABI call absolute code[i], it <- return addr, code <- return segment
     0111 iiiiiiii COFI call offset pc ± i, it <- return offset (-i + 2)
     10xx iiiiiiii      (reserved w/ immediate)
     110x iiiiiiii      (reserved w/ immediate)
     1110 iiiiiiii GETI it <- i
     1111 xxxxxxxx EXT1 extended encoding for "future-proofing"