nx_emu_armv7a.nx

nx_emu_armv7a.nx -- sovereign ARMv7-A (32-bit ARM) interpreter (NX-EMU). Little-endian, fixed 32-bit ARM (not Thumb) encoding, 16 GPRs + NZCV. Linux EABI: svc, r7=num, args r0.., exit=1 (code in r0). NO qemu. license_tier: ORIGINAL ---- 2026-09-03, ISA LANE: WHAT WAS MEASURED AND WHAT WAS BUILT ---- The incumbent decoded a useful subset and had FIVE structural gaps. Each was found by reading the decoder, not by guessing, and each one failed in the SILENT direction -- the interpreter kept running and produced a wrong number rather than saying it could not do the job: 1. THE CONDITION FIELD (bits 31:28) WAS NEVER READ. Every ARM instruction is predicated; BEQ, MOVNE and B were all executed unconditionally. So the emulator could not run a LOOP at all: a backward BNE was always taken, the program spun to the step budget, and the budget path returned the initial result 0 -- which the caller reads as exited-with-status-0, i.e. SUCCESS. A hang was indistinguishable from a pass. 2. THERE WERE NO N, Z OR V FLAGS, only C. Nothing could set them. 3. CMP / CMN / TST / TEQ (opcodes 8..11) claimed handled=1 and then matched no branch, so a comparison was a silent no-op -- the worst possible shape, because it looks exactly like execution. 4. EOR, RSB, RSC, BIC and MVN were the same silent no-op. 5. THE SHIFTER WAS ABSENT: operand2 in register form was taken as the bare register, so add r0, r0, r1, lsl 3 quietly added r1. LDR/STR ignored the B (byte), P (pre/post) and W (writeback) bits and misread a register-offset form as an immediate one. All five are implemented here. Two further classes are now NAMED rather than misdecoded: the extra load/store space (halfword, signed byte, SWP -- told apart from data processing by bit7=1 AND bit4=1) and the cond 0b1111 unconditional-instruction space return A7_UNSUPPORTED instead of being run as a data-processing op. NON-COMPLETION IS THREE NAMED STATES, NOT ONE NEGATIVE WORD. An unimplemented instruction class and a miscomputed value need OPPOSITE fixes, and a program that walked off its image is neither. A7_UNSUPPORTED (-1) a class this interpreter does not decode A7_RANOFF (-2) pc left the image with no exit syscall A7_FAULT (-3) negative pc, out-of-range access, step budget