USYST

MON 60 subfunction USYST = 075B (octal) = 0x3D = 61 decimal. NPL purpose (authoritative, 5P-P2-MON60.NPL): CHECK IF CURRENT USER IS USER SYSTEM, server handler ITSTUSER.

All addresses are OCTAL ND-100 word addresses, BANK 1, base 0. Source: SINTRAN/ND500/nd-500-mon/nd-500-mon-j04.prog.asm

Named by subfunction (USYST). No operator command name is invented here.

Handler location

USYST is a privilege gate: it takes no input parameters and is issued for its skip/direct return only. Four call sites.

Call site	JPL	ptr -> thunk	Enclosing routine	Error (callsite+1)	Success (callsite+2)	Status
006325	JPL I 26	006353 -> 146605 (SAA 75)	002662 (fs 000331, main interpreter)	006326 JPL I -176 -> ptr 006130 = 002673	006327 LDD 25 (continues)	PROVEN
006411	JPL I -36	006353 -> 146605	002662	006412 JPL I 142 -> ptr 006554 = 002673	006413 LDD 143	PROVEN
006447	JPL I -74	006353 -> 146605	002662	006450 JPL I 104 -> ptr 006554 = 002673	006451 LDD 111	PROVEN
073461	JPL I 50	073531 -> 146605	073412 (fs 000223)	073462 JPL I 43 -> ptr 073525 = 177327 (LEAVE-value, returns error to caller)	073463 (continues)	PROVEN

All four resolve to the single USYST thunk 146605. The three 006xxx sites share the same pointer word 006353; both 006411/006447 error paths share pointer word 006554 = routine 002673 (the interpreter error reporter).

Thunk bytes (verified): 146605=170475 (SAA 75), 146606=125001, 146607=146244.

MON 60 subfunction used

Subfn	Octal / Hex / Dec	Thunk	Parameters	Skip/Error
USYST	075B / 0x3D / 61	146605	none (no LDX ,B -176 / STx ,X n precedes any of the four sites)	success = current user IS SYSTEM; error = NOT system

What it does

Each call site issues MON 60 USYST with no parameter block and branches on the return. On the SKIP (success) return the user is user SYSTEM and the caller proceeds; on the DIRECT (error) return the caller diverts to the interpreter error reporter 002673 (three interpreter sites) or performs a LEAVE-with-value returning an error to the caller of routine 073412 (073461).

USYST guards operations that must be restricted to user SYSTEM.

Unknown / inferred

• PROVEN: no input parameters are marshalled at any of the four call sites (no LDX ,B -176 + STx ,X n sequence immediately precedes them).
• INFERRED: success = "is SYSTEM", error = "not SYSTEM". The return polarity (skip=success, direct=error) is PROVEN from the gateway; that "success" means the user IS SYSTEM rests on the NPL purpose string, not a traced server result.
• INFERRED (role): 002673 is the interpreter error reporter; its entry address and that the error paths reach it are PROVEN. 177327 is the runtime LEAVE-value helper (PROVEN, prog.md sec 4.3).