67B OutBufferSpace¶

In progress MON 67B (55 decimal) · Mnemonic OSIZE · Group: Input and Output Monitor Calls (manual section 2.5)

Available from: All programs (manual compatibility box)

Emulation source: src/handlers/mon_67B_OutBufferSpace.c

Description¶

Gets the number of free bytes in the output buffer (number of bytes which can be written before the program must wait). Terminals and other character devices place output in a buffer. Monitor calls like OutByte writes to this buffer.

Use ExecutionInfo to get the logical device number for terminals. You can specify 1 for your own terminal.
This monitor call is not available for internal devices. Use InBufferSpace and subtract this size from the inbuffer size.

Parameters¶

Name	Type	Direction	Description
`DeviceNumber`	INTEGER2	In	Logical device number. See appendix B. Use 1 for your own terminal.
`NoOfBytes`	INTEGER2	Out	Number of free bytes in output buffer (output, returned in W1).

Direction: In = the program supplies the value, Out = the call returns it, In/Out = both.

Compatibility¶

Machines	Users	Programs
ND-100 and ND-500	All users	All programs

The manual's compatibility box for this call, word for word.

Yes/no fields from the YAML extraction (not in the manual's words):

ND-100	ND-500	User programs	RT programs	System programs
Yes	Yes	No	No	No

Examples¶

From the manual (OCR text, not corrected).

PLANCFORTRANPascalCOBOLASSEMBLY-500MAC

INTEGER : DeviceNumber, NoOfBytes
...
ON ROUTINEERROR DO
    IF ErrCode > 0 THEN ...
ENDON
Monitor_Call('OutBufferSpace', DeviceNumber, NoOfBytes)

INTEGER DeviceNumber, NoOfBytes
...
Monitor_Cal1('OutBufferSpace', DeviceNumber, NoOfBytes)
IF (ErrCode .NE. 0) THEN ...

DeviceNumber, NoOfBytes : INTEGER2;
...
OutBufferSpace(DeviceNumber, NoOfBytes);
IF ErrCode <> 0 THEN ...

01 DeviceNumber  COMP.
01 NoOfBytes     COMP.
01 ErrCode       COMP.
...
MONITOR-CALL "OutBufferSpace" USING DeviceNumber, NoOfBytes.
CALL "CbError" USING ErrCode.
IF ErrCode NOT = 0 GO ...

DeviceNumber : W BLOCK 1
NoOfBytes : W BLOCK 1
ErrCode : W BLOCK 1
OutBufferSpace : EQU 37B9 + 67B
    ...
    CALLG OutBufferSpace, 1, DeviceNumber
    IF K GO ERROR
    W1 =: NoOfBytes           %Result is returned in W1 register.
    ...
ERROR : W1 =: ErrCode        %ErrorCode in W1 register.

    LDT DEVNO                %Logical device number.
    MON 67                   %Monitor call OutBufferSpace.
    JMP ERROR                %Error return from monitor call.
    STA COUNT                %Normal return, store number of bytes.
ERROR,
    ...                      %Error number in register A.
DEVNO, ...
COUNT, 0                     %Number of bytes free space in outbuffer.

ndmonlib implementation¶

In progress Registered MON_STATUS_IN_PROGRESS: partly implemented. The dispatcher calls the handler.


Handler	`mon_67B_OutBufferSpace`
Code lines	31 (non-blank, non-comment lines in the file)

Notes from the handler source¶

src/handlers/mon_67B_OutBufferSpace.c line 54

For emulation, we always report a large buffer available
since we don't actually have output buffer constraints

Emulation research¶

Source

This section comes from the emulation: block of the call's YAML file in the NDInsight repo. It records what was learned while implementing the call in nd500x; its status is nd500x's, not ndmonlib's.


Status (nd500x)	stub
nd500x handler	nd500x/src/libmon/handlers/mon_67B_OutBufferSpace.c
Last updated	2026-07-17

Stub behaviour¶

RETURNS A CONSTANT - SAY SO. 67B OSIZE always answers 2048 free bytes (DEFAULT_BUFFER_SIZE) for any legal device, regardless of how much has been written. nd500x has NO output buffer at all: 2B/24B/162B/504B write straight through to the console and never block, so there is no free-space figure to report and nothing the answer could be measured against. A program that polls 67B to pace its output will see infinite space and never throttle - which is harmless here precisely because writes never block.

Parameter notes¶

1. NoOfBytes

Field	Value
Note	Returned in W1/I1 via ctx->set_i1 AND, if a second CALLG argument is present, written to it as a 32-bit word. The manual documents the I1 return; the OUT parameter write is defensive.
Verified	No

Return contract¶

Success: K flag cleared; NoOfBytes in I1 (always 2048).
Errors

Code Octal Meaning

124 174B Illegal parameter (a file number was passed)

111 157B Missing parameter (no CALLG args)

Verified¶

Claim	Evidence
File numbers are rejected.	is_mass_storage_file(device_no) -> error 124 (174B) in mon_67B_OutBufferSpace.c.

Unverified¶

THAT 2048 IS A PLAUSIBLE FIGURE. It is nd500x's own DEFAULT_BUFFER_SIZE, not a real SINTRAN buffer size read from anywhere. The real per-device output buffer size is not in the scanned pages.
THE CARVE WAS NOT MINED FOR THIS ENTRY. A carve folder exists at NDInsight/tools/sintran-segment-carver/versions/L-VSX-500/re/mon-analysis/067B-OutBufferSpace/ and has NOT been read into this block. It may well carry the real buffer accounting.
The manual says "This monitor call is not available for internal devices." nd500x does not model internal devices and so cannot reject them; it rejects only file numbers. The error code for the internal-device case is unknown.
Error 124 (174B) for the file-number case is a CHOICE, not a read value.
NO OBSERVED CALLER. No traced program issues 67B.

Sources¶

Doc	Note
SINTRAN III Monitor Calls (ND-860228.2 EN)	The manual body of this YAML.

Source¶

SINTRAN III Monitor Calls (ND-860228.2 EN), page 375.

Code	Octal	Meaning
124	174B	Illegal parameter (a file number was passed)
111	157B	Missing parameter (no CALLG args)