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SINTRAN III SCSI Commands Analysis

Document Created: 2025-10-13 Source Files: IP-P2-SCSI-DISK.NPL, IP-P2-SCSI-DRIV.NPL Purpose: Document all SCSI commands used, their response requirements, and custom command support

Table of Contents

  1. SCSI Commands Used by SINTRAN
  2. Command Details and Response Requirements
  3. Custom SCSI Command Support
  4. INQUIRY Command Support
  5. Implementation Requirements

SCSI Commands Used by SINTRAN

Overview

SINTRAN III uses two command mapping arrays (SCSF1 and SCSF2) that map SINTRAN function codes (0-77 octal) to SCSI opcodes. The choice of array depends on the SCSI device type:

  • SCSF1: Used for Direct Access Devices (Type 0, 4, 5)
  • SCSF2: Used for Sequential Access Devices (Type 1, 2, 3 - Tape devices)

Command Mapping Tables

SCSF1 - Direct Access Devices (Disks)

Function Octal SCSI Opcode Command Name Notes
0 00 0x08 READ(6) Read sectors
1 01 0x0A WRITE(6) Write sectors
2 02 0x2F VERIFY(6) Verify data
3 03 0x2F VERIFY(6) Verify with compare
4 04 0x0B SEEK(6) Seek to address
16 20 0x00 TEST UNIT READY Check device status
19 23 0x15 MODE SELECT(6) Set device parameters
21 25 0x1A MODE SENSE(6) Query device parameters
28 34 0x16 RESERVE DEVICE Reserve for exclusive use
29 35 0x17 RELEASE DEVICE Release reservation
33 41 0x04 FORMAT UNIT Format disk
34 42 Special READ CAPACITY(10) Get disk size (auto-inquiry)
36 44 0x08 READ(6) Read control area
37 45 0x0A WRITE(6) Write control area
48 60 0x08 READ(6) Read (double address)
49 61 0x0A WRITE(6) Write (double address)
50 62 0x2F VERIFY(6) Verify (double address)
51 63 0x2F VERIFY(6) Verify compare (double addr)
54 66 0x08 READ(6) Read with special handling
57 71 0x2E WRITE AND VERIFY Write with verify
59 73 0x00 TEST UNIT READY Device ready check
60 74 User USER COMMAND Execute user-specified CDB
61 75 0x12 INQUIRY Device identification

SCSF2 - Sequential Access Devices (Tapes/Streamers)

Function Octal SCSI Opcode Command Name Notes
0 00 0x08 READ(6) Read tape blocks
1 01 0x0A WRITE(6) Write tape blocks
2 02 0x13 VERIFY(6) Verify tape data
3 03 0x13 VERIFY(6) Verify with compare
7 07 0x19 ERASE Erase tape
8 10 0x11 SPACE BLOCKS Space forward/backward
9 11 0x11 SPACE FILEMARKS Space over filemarks
10 12 0x10 WRITE FILEMARKS Write end-of-file marks
11 13 0x01 REWIND Rewind to beginning
12 14 0x19 ERASE Erase (gap)
13 15 0x11 SPACE BLOCKS Space reverse
14 16 0x11 SPACE BLOCKS Space forward
15 17 0x1B START/STOP UNIT Unload tape
16 20 0x00 TEST UNIT READY Device status
17 21 0x01 REWIND Rewind
18 22 0x01 REWIND Rewind
19 23 0x15 MODE SELECT(6) Set tape parameters
21 25 0x1A MODE SENSE(6) Query tape parameters
22 26 0x08 READ(6) Read variable blocks
23 27 0x0A WRITE(6) Write variable blocks
24 30 0x1B START/STOP UNIT Load tape
28 34 0x16 RESERVE DEVICE Reserve device
29 35 0x17 RELEASE DEVICE Release device
34 42 0x05 READ BLOCK LIMITS Query block size limits
48 60 0x08 READ(6) Read (special mode)
49 61 0x0A WRITE(6) Write (special mode)
50 62 0x13 VERIFY(6) Verify (special mode)
51 63 0x13 VERIFY(6) Verify compare
54 66 0x08 READ(6) Read with handling
56 70 0x1B START/STOP UNIT Retension tape
59 73 0x00 TEST UNIT READY Device ready
60 74 User USER COMMAND Execute user-specified CDB
61 75 0x12 INQUIRY Device identification
62 76 0x11 SPACE BLOCKS Space to end of data

Automatic Commands

These commands are issued automatically by the driver:

SCSI Opcode Command When Issued Source Line
0x03 REQUEST SENSE After CHECK CONDITION status 1359-1364
0x12 INQUIRY Device initialization 1223-1227
0x25 READ CAPACITY(10) After INQUIRY for disks 1234
0x05 READ BLOCK LIMITS After INQUIRY for tapes 1237
0x1A MODE SENSE(6) Tape initialization Line 544
0x15 MODE SELECT(6) After MODE SENSE for tapes Line 558

Command Details and Response Requirements

1. TEST UNIT READY (0x00)

Function Codes: 16 (20 octal), 59 (73 octal)

Command Block: 

Byte 0: 0x00 | (LUN << 5)
Byte 1-4: 0x00
Byte 5: Control byte

Expected Response: - GOOD status (0x00): Device is ready - CHECK CONDITION: Device not ready, REQUEST SENSE will provide details

SINTRAN Behavior: - No data phase - Used to check if device is operational - Retries with wait on BUSY status

2. REQUEST SENSE (0x03)

Automatically issued after CHECK CONDITION status

Command Block: 

Byte 0: 0x03 | (LUN << 5)
Byte 1-2: 0x0000
Byte 3: Reserved
Byte 4: Allocation length (sense buffer size)
Byte 5: Control byte

Expected Response: Must return extended sense data (minimum 8 bytes):

Byte 0: Error code (0x70 = current error, 0x71 = deferred error)
Byte 1: Reserved
Byte 2: Sense Key (bits 0-3)
        - 0x00: NO SENSE
        - 0x01: RECOVERED ERROR
        - 0x02: NOT READY
        - 0x03: MEDIUM ERROR
        - 0x04: HARDWARE ERROR
        - 0x05: ILLEGAL REQUEST
        - 0x06: UNIT ATTENTION
        - 0x0B: ABORTED COMMAND
        - 0x0C: COPY ABORTED (for COPY command)
Byte 3-6: Information bytes
Byte 7: Additional sense length
Byte 8+: Additional sense data

Critical Bits (Line 1200-1209): 

Bit 15: Must be 1 for extended sense
Bits 5-7: ILI (Illegal Length), EOM (End of Media), EOF flags
Bits 0-3: Sense key

SINTRAN Special Handling: - Sense Key = 6 (UNIT ATTENTION): Forces re-initialization (INQUIRY) at line 1210-1212 - Sense Key = 1 or 3: Logged as corrected/medium error - Sense Key = 12: Interpreted as COPY ABORTED - Sense Key = 13: ABORTED COMMAND - triggers retry

Source: Lines 1186-1214

3. INQUIRY (0x12)

Function Code: 61 (75 octal) Also automatically issued during initialization

Command Block (Line 1224-1227): 

Byte 0: 0x12 | (LUN << 5)
Byte 1: 0x00
Byte 2: 0x00 (Page code)
Byte 3: Reserved
Byte 4: Allocation length (usually 36+ bytes)
Byte 5: Control

Expected Response (Standard INQUIRY Data):

Byte 0: Peripheral Device Type
        - 0x00: Direct Access (disk)
        - 0x01: Sequential Access (tape)
        - 0x02: Printer
        - 0x03: Processor
        - 0x04: Write-once
        - 0x05: CD-ROM
        - 0x7F: Logical unit not present
Byte 1: RMB (bit 7 = removable)
Byte 2: Version
Byte 3: Response Data Format (must be 2)
Byte 4: Additional length (n-4)
Byte 5-6: Reserved
Byte 7: Flags
Byte 8-15: Vendor ID (8 bytes ASCII)
Byte 16-31: Product ID (16 bytes ASCII)
Byte 32-35: Product Revision (4 bytes ASCII)

SINTRAN Processing (Lines 1230-1265):

  1. Device Type Check (Line 1232-1242):

    • Type 0, 3, 4 → Direct Access, issues READ CAPACITY(10) next
    • Type 1 → Sequential Access, issues READ BLOCK LIMITS next
    • Type 0x7F → Returns "NO SUCH LUN" error

  2. For Disks - READ CAPACITY(10) follows (Line 1234):

READ CAPACITY Command: 

Byte 0: 0x25
Byte 1-8: Reserved
Byte 9: Control

READ CAPACITY Response: 

Bytes 0-3: Last Logical Block Address (big-endian)
Bytes 4-7: Block Length in bytes (big-endian)

Stored at: Line 1252-1254 → SURSZ (device record size)

  1. For Tapes - READ BLOCK LIMITS follows (Line 1237):

READ BLOCK LIMITS Command: 

Byte 0: 0x05
Byte 1-4: Reserved
Byte 5: Control

READ BLOCK LIMITS Response: 

Byte 0: Reserved
Bytes 1-3: Maximum block length
Bytes 4-5: Minimum block length

Processing (Lines 1257-1264): - Fixed block mode if min = max - Variable block mode if different - Block size stored in SURSZ

Required Flags Set: - Bit 5SCIN: Initialization complete - Bit 5SCDA: Direct access device (if applicable) - Bit 5SFBM: Fixed block mode (tapes) - Bit 5SVBS: Variable block size (tapes)

Source: Lines 1216-1314

4. READ(6) (0x08)

Function Codes: 0, 36, 48, 54, 60, 66

Command Block (Lines 1533-1539):

6-byte format: 

Byte 0: 0x08 | (LUN << 5) | (MSB 3 bits of address)
Byte 1: Middle byte of address
Byte 2: LSB of address
Byte 3: Transfer length (0 = 256 blocks)
Byte 4: Control

10-byte format (for large addresses): 

Byte 0: 0x28 (READ(10))
Byte 1: Flags
Bytes 2-5: Logical Block Address (big-endian)
Bytes 6-7: Reserved
Bytes 7-8: Transfer Length
Byte 9: Control

SINTRAN uses 10-byte format when: - Address > 0x1FFFFF (21 bits) - Line 1531

Data Phase: - IN (Device → Host) - Transfer size = Block size × Transfer length - Block size obtained from INQUIRY/READ CAPACITY

Expected Status: - GOOD (0x00): Data transferred successfully - CHECK CONDITION: Error occurred, REQUEST SENSE provides details

Error Handling: - Retries on UNIT ATTENTION (sense key 6) - Retries on ABORTED COMMAND (sense key 13) - Fails on MEDIUM ERROR (sense key 3)

Source: Lines 1476-1545, CACOB routine

5. WRITE(6) (0x0A)

Function Codes: 1, 37, 49, 55, 61

Command Block: Same format as READ(6)

Data Phase: - OUT (Host → Device) - Transfer size = Block size × Transfer length

Expected Status: Same as READ

Optical Disk Special Handling: - Function 71 (WRITE AND VERIFY) uses opcode 0x2E - See IP-P2-SCSI-OPDI.NPL for write recovery mechanism

Source: Same as READ

6. MODE SENSE(6) (0x1A)

Function Code: 21 (25 octal) Also automatic for tape initialization

Command Block (Line 544): 

Byte 0: 0x1A | (LUN << 5)
Byte 1: DBD flag (Disable Block Descriptors)
Byte 2: Page Control (bits 6-7) | Page Code (bits 0-5)
Byte 3: Reserved
Byte 4: Allocation Length
Byte 5: Control

Expected Response:

Mode Parameter Header: 

Byte 0: Mode Data Length
Byte 1: Medium Type
Byte 2: Device-Specific Parameter
        - Bit 7: Write Protect (1 = protected)
Byte 3: Block Descriptor Length

Block Descriptor (if present): 

Bytes 0-3: Number of blocks (or density code in byte 0)
Byte 4: Reserved
Bytes 5-7: Block length

SINTRAN Processing (Lines 992-1004): - Extracts write-protect flag from byte 2, bit 7 - Extracts density code from byte 4 of block descriptor - Stores in CFORM field

Used For: - Determining tape density - Checking write protection - Querying block size

Source: Lines 542-564, 989-1004

7. MODE SELECT(6) (0x15)

Function Code: 19 (23 octal) Also automatic after MODE SENSE for tapes

Command Block (Line 558): 

Byte 0: 0x15 | (LUN << 5)
Byte 1: PF (Page Format, bit 4) | SP (Save Pages, bit 0)
Byte 2: Reserved
Byte 3: Reserved
Byte 4: Parameter List Length
Byte 5: Control

Data Phase OUT - Mode Parameter List:

Header: 

Byte 0: Reserved
Byte 1: Reserved
Byte 2: Reserved
Byte 3: Block Descriptor Length

Block Descriptor (Lines 553-557): 

Byte 0: Density Code
Bytes 1-3: Reserved
Byte 4: Reserved
Bytes 5-7: Block Length (0 for variable blocks)

SINTRAN Sets: - Density code from previous MODE SENSE or user parameter - Block size: 1024 (0x400) for fixed block mode, 0 for variable

Used For: - Setting tape density - Setting block size mode (fixed vs variable)

Source: Lines 546-577, MODE SELECT logic

8. VERIFY(6) (0x2F)

Function Codes: 2, 3, 50, 51, 62, 63

Command Block: 

Byte 0: 0x2F | (LUN << 5) | (Address MSB)
Byte 1: Address middle
Byte 2: Address LSB
Byte 3: Verification Length
Byte 4: Control
        - Bit 1: BYTCHK (Byte Check) - compare with host data

Two Modes:

  1. BYTCHK = 0: Verify media only (no data transfer)
  2. BYTCHK = 1: Compare with host data (Data OUT phase)

Expected Status: - GOOD: Verification passed - CHECK CONDITION: Verification failed or media error

SINTRAN Note: Line 198: "COMPARE NOT IMPLEMENTED" - SINTRAN may not fully support BYTCHK=1 mode

Source: SCSF1/SCSF2 arrays, lines 1452-1469

9. WRITE AND VERIFY (0x2E)

Function Code: 57 (71 octal)

Command Block: 

Byte 0: 0x2E | (LUN << 5)
Byte 1: Flags
Bytes 2-5: Logical Block Address
Bytes 6-7: Reserved
Bytes 7-8: Transfer Length
Byte 9: Control

Behavior: - Writes data to medium - Immediately verifies written data - Single operation from host perspective

Used By: - Optical disk driver for critical writes - See CCRWO (Compare-Compare-Rewrite-Optical) in IP-P2-SCSI-OPDI.NPL

Source: SCSF1 array index 69

10. SEEK(6) (0x0B)

Function Code: 4

Command Block: 

Byte 0: 0x0B | (LUN << 5) | (Address MSB)
Byte 1: Address middle
Byte 2: Address LSB
Byte 3: Reserved
Byte 4: Control

Purpose: - Pre-position disk head to reduce latency on next READ/WRITE - Used by elevator algorithm (DSORT) for optimization

Expected Status: - GOOD: Seek complete - CHECK CONDITION: Seek error

Source: SCSF1 array index 4

11. FORMAT UNIT (0x04)

Function Code: 33 (41 octal)

Command Block: 

Byte 0: 0x04 | (LUN << 5)
Byte 1: Format Options
Byte 2: Vendor Specific
Byte 3: Interleave (MSB)
Byte 4: Interleave (LSB)
Byte 5: Control

Optional Data Phase: - OUT phase if defect list provided - No data phase for simple format

Expected Status: - GOOD: Format complete - CHECK CONDITION: Format failed

SINTRAN Note: - Used for disk formatting - May take significant time (several minutes to hours)

Source: SCSF1 array index 34

12. RESERVE/RELEASE DEVICE (0x16/0x17)

Function Codes: 28 (34 octal), 29 (35 octal)

RESERVE Command: 

Byte 0: 0x16 | (LUN << 5)
Byte 1-4: Reserved
Byte 5: Control

RELEASE Command: 

Byte 0: 0x17 | (LUN << 5)
Byte 1-4: Reserved
Byte 5: Control

Purpose: - RESERVE: Lock device for exclusive use by this initiator - RELEASE: Unlock device

Expected Status: - GOOD: Reservation accepted/released - RESERVATION CONFLICT (0x18): Device already reserved by another initiator

SINTRAN Handling (Lines 649-651, 1144-1146): - Tracks reservation state in OPSTA bit 4SRES - Returns error code 3210 (RESERVATION CONFLICT) to application

Source: SCSF1/SCSF2 arrays index 28-29

13. Tape-Specific Commands

REWIND (0x01)

Function Codes: 11 (13 octal), 17, 21

Command Block: 

Byte 0: 0x01 | (LUN << 5)
Byte 1: Immediate bit (bit 0)
Byte 2-4: Reserved
Byte 5: Control

Immediate Mode: - Bit 0 = 1: Command returns immediately, rewind continues in background - Bit 0 = 0: Command waits for rewind to complete

WRITE FILEMARKS (0x10)

Function Code: 10 (12 octal)

Command Block: 

Byte 0: 0x10 | (LUN << 5)
Byte 1: Reserved
Bytes 2-4: Number of filemarks (3 bytes, big-endian)
Byte 5: Control

SPACE (0x11)

Function Codes: 8-10, 13-14, 62

Command Block: 

Byte 0: 0x11 | (LUN << 5)
Byte 1: Code (bits 0-1)
        - 0x00: Space blocks
        - 0x01: Space filemarks
        - 0x03: Space to end of data
Bytes 2-4: Count (signed 3-byte value, can be negative for reverse)
Byte 5: Control

ERASE (0x19)

Function Code: 7

Command Block: 

Byte 0: 0x19 | (LUN << 5)
Byte 1: Long bit (bit 0)
Byte 2-4: Reserved
Byte 5: Control

START/STOP UNIT (0x1B)

Function Codes: 15 (17 octal - unload), 24 (30 octal - load), 56 (70 octal - retension)

Command Block: 

Byte 0: 0x1B | (LUN << 5)
Byte 1: Immediate bit (bit 0)
Byte 2-3: Reserved
Byte 4: Power/LoEj/Start
        - Bit 0: Start (1 = start, 0 = stop)
        - Bit 1: LoEj (Load/Eject)
Byte 5: Control

Operations: - Load: LoEj=1, Start=1 - Unload: LoEj=1, Start=0 - Retension: Special vendor-specific mode

Source: SCSF2 array, tape functions

Custom SCSI Command Support

Function 74: Execute User-Specified SCSI Command Block

✅ YES - Applications CAN send custom SCSI commands including INQUIRY

Function Code: 60 (74 octal)

API Entry Point (Line 1100-1127): 

SCSID: A=:X.HSTAT:=L=:X."FINISH":=B=:X.SCUDF
       T=:X.SCTRG:=:X; 77/\X.ABFUN; X:=T
       ...
       IF A=74 THEN
          CALL GUSCB     % USER SPECIFIED COMMAND
       ...

GUSCB Routine (Lines 1385-1392): 

GUSCB: ABPA3=:SUIBC; A:=L=:SAVA:=6=:L       % NUMBER OF WORDS (6 = 12 bytes)
       ABPA2; X:=SMBP1; T:=SMBP2; *MOVPP    % MOVE COMMAND BLOCK FROM USER MEMORY
       IF ABFUN SHZ -14=0 THEN 377/\SUICO FI
       T:=SAVA=:P

How It Works

  1. User builds SCSI Command Descriptor Block (CDB) in memory

  2. Calls SCSID with:

    • ABFUN = 74 (octal) with LUN in bits 6-8
    • MEMAD = Data buffer address (for data-in/data-out phases)
    • ABPA2 = Pointer to CDB (Command Descriptor Block)
    • ABPA3 = Byte count for data transfer
    • A register = Driver control flags

  3. Driver copies 12-byte CDB from user memory (line 1389)

  4. Driver executes SCSI command through normal protocol (EXCOM routine)
  5. Results returned in user's data buffer

Parameters

ABSTR Parameter Block:

struct ABSTR {
    uint16_t ABFUN;      // Function code = 74 (octal)
                        // Bits 0-5: Function (74)
                        // Bits 6-8: LUN (0-7)

    uint16_t MEMAD_HI;   // Data buffer address (high word)
    uint16_t MEMAD_LO;   // Data buffer address (low word)

    uint16_t ABPA2_HI;   // CDB address (high word)
    uint16_t ABPA2_LO;   // CDB address (low word)
                        // Points to 12-byte command block

    uint16_t ABPA3_HI;   // Byte count (high word)
    uint16_t ABPA3_LO;   // Byte count (low word)
                        // Data transfer length in bytes
};

A Register Control Flags:

Bit 0-3: Log₂ of timeout (seconds = 2^n)
Bit 4:   Use SELECT without ATN
Bit 5:   Don't use disconnect/reconnect
Bit 6:   Return on command accepted (before data transfer complete)

Example: Sending INQUIRY Command

Step 1: Build INQUIRY CDB in memory:

uint8_t inquiry_cdb[12] = {
    0x12,           // INQUIRY opcode
    0x00,           // LUN=0, no EVPD
    0x00,           // Page code
    0x00,           // Reserved
    0x24,           // Allocation length = 36 bytes
    0x00,           // Control
    0x00, 0x00,     // Reserved
    0x00, 0x00,     // Reserved
    0x00, 0x00      // Reserved
};

Step 2: Allocate data buffer:

uint8_t inquiry_data[36];  // Buffer for INQUIRY response

Step 3: Set up ABSTR parameters:

struct ABSTR params;
params.ABFUN = 074;                    // Function 74 (octal), LUN 0
params.MEMAD = (uint32_t)inquiry_data; // Response buffer address
params.ABPA2 = (uint32_t)inquiry_cdb;  // CDB address
params.ABPA3 = 36;                     // Expect 36 bytes response

Step 4: Call SCSID:

; ND-100 Assembly example
        T = &params
        X = device_datafield
        B = lun_datafield
        A = 4              ; Timeout = 2^4 = 16 seconds
        JPL I (SCSID)
        JMP ERROR_EXIT
        JMP BUSY_EXIT
        JMP SUCCESS_EXIT

SUCCESS_EXIT:
        ; inquiry_data now contains device information
        ; Parse bytes 0-35 for device type, vendor, product, etc.

Step 5: Parse results:

// After successful return:
uint8_t device_type = inquiry_data[0] & 0x1F;
bool removable = (inquiry_data[1] & 0x80) != 0;
char vendor[9];
memcpy(vendor, &inquiry_data[8], 8);
vendor[8] = '\0';

char product[17];
memcpy(product, &inquiry_data[16], 16);
product[16] = '\0';

char revision[5];
memcpy(revision, &inquiry_data[32], 4);
revision[4] = '\0';

INQUIRY Command Support

Built-in INQUIRY Support

Function Code: 61 (75 octal)

Applications can also use the built-in INQUIRY support instead of Function 74:

Automatic Processing: - Sends INQUIRY command - For disks: Automatically follows with READ CAPACITY(10) - For tapes: Automatically follows with READ BLOCK LIMITS - Parses device type - Stores block size in device data structure - Sets initialization flags

Usage:

struct ABSTR params;
params.ABFUN = 075;          // Function 75 (octal) = INQUIRY
params.MEMAD = buffer_addr;   // Buffer for extended information
params.ABPA2 = 0;            // Not used
params.ABPA3 = 100;          // Buffer size for format info

// Call SCSID
// After return, device is fully initialized and ready

What's Returned:

For Function 42 (Inquiry + Read Capacity), returned in MEMAD buffer:

struct FormatInfo {
    uint32_t disk_size;      // Total blocks on disk
    uint32_t block_size;     // Bytes per block
    // ... other fields depend on device type
};

Advantages of Function 75 vs Function 74:

Aspect Function 75 (Built-in) Function 74 (Custom)
Setup Simple - just call with buffer Must build CDB manually
Parsing Automatic Must parse response manually
Follow-up Auto READ CAPACITY/BLOCK LIMITS Must send separately if needed
Initialization Sets device flags automatically Must track device state manually
Use Case Device initialization Advanced diagnostics, custom commands

Implementation Requirements

For C# SCSI Emulator

To properly support SINTRAN's SCSI expectations, the C# emulator must:

1. Implement All Commands

Support all commands in SCSF1/SCSF2 tables, particularly:

  • ✅ Must Have:
    • TEST UNIT READY
    • REQUEST SENSE (with proper extended sense format)
    • INQUIRY (with proper device type response)
    • READ CAPACITY(10) or READ BLOCK LIMITS
    • READ(6) and WRITE(6)
    • MODE SENSE(6) and MODE SELECT(6)
  • ⚠️ Should Have:
    • SEEK(6) for performance
    • VERIFY(6) for data integrity
    • RESERVE/RELEASE for multi-host
    • START/STOP UNIT for removable media
  • 🔧 Optional:
    • FORMAT UNIT
    • WRITE AND VERIFY
    • Tape commands (if emulating tape)

2. Status Handling

Return proper SCSI status:

public enum ScsiStatus : byte
{
    Good = 0x00,
    CheckCondition = 0x02,
    ConditionMet = 0x04,
    Busy = 0x08,
    Intermediate = 0x10,
    IntermediateConditionMet = 0x14,
    ReservationConflict = 0x18,
    CommandTerminated = 0x22,
    QueueFull = 0x28
}

For CHECK CONDITION, prepare valid extended sense data.

3. REQUEST SENSE Response

Must return valid extended sense data:

public class ExtendedSenseData
{
    public byte ErrorCode = 0x70;        // Current error
    public byte SenseKey;                // 0x00-0x0F
    public byte[] Information = new byte[4];
    public byte AdditionalSenseLength = 10;
    public byte[] CommandSpecificInfo = new byte[4];
    public byte AdditionalSenseCode;     // ASC
    public byte AdditionalSenseCodeQualifier; // ASCQ
    public byte FieldReplaceableUnitCode;
    public byte[] SenseKeySpecific = new byte[3];
}

Critical Sense Keys for SINTRAN:

  • 0x00 (NO SENSE): Operation succeeded
  • 0x01 (RECOVERED ERROR): Error but data is valid
  • 0x02 (NOT READY): Device not ready
  • 0x03 (MEDIUM ERROR): Unrecoverable read/write error
  • 0x05 (ILLEGAL REQUEST): Invalid command or parameter
  • 0x06 (UNIT ATTENTION): Device reset or media changed - triggers re-initialization
  • 0x0B (ABORTED COMMAND): Command aborted - triggers retry
  • 0x0C (COPY ABORTED): COPY command failed

4. INQUIRY Response

Must return proper INQUIRY data:

public class InquiryData
{
    public byte PeripheralDeviceType;   // 0=disk, 1=tape, 5=CD-ROM
    public bool Removable;
    public byte Version = 0x02;         // SCSI-2 compliance
    public byte ResponseDataFormat = 0x02;
    public byte AdditionalLength = 31;  // n-4 where n=36
    public byte[] Vendor = new byte[8]; // ASCII, space-padded
    public byte[] Product = new byte[16]; // ASCII, space-padded
    public byte[] Revision = new byte[4]; // ASCII

    // Followed by READ CAPACITY or READ BLOCK LIMITS
}

5. Function 74 Support

Must support user-specified CDB execution:

public void ExecuteUserCommand(byte[] cdb, byte[] dataBuffer,
                               int dataLength, bool dataIn)
{
    // 1. Validate CDB (6, 10, or 12 bytes)
    // 2. Parse opcode from cdb[0]
    // 3. Execute command
    // 4. Transfer data if dataLength > 0
    // 5. Return status
}

Security Considerations: - Consider limiting dangerous commands (FORMAT UNIT, WRITE BUFFER, etc.) - Or require special permissions for raw SCSI access - Log all Function 74 commands for audit

6. Interrupt Handling

As documented in SCSI-C#-Implementation-Guide.md:

  • Generate interrupts on phase changes
  • Set RSTAU bit 11 (NCR interrupt)
  • Trigger Level 11 CPU interrupt
  • Wait for WCONT=5 (resume) before continuing

Reference: See previous analysis in SCSI-C#-Implementation-Guide.md

7. Response Timing

SINTRAN expects responses within timeout period: - Default: 2^4 = 16 seconds - Can be specified in A register bits 0-3 - Return BUSY status if operation will take longer - After BUSY, SINTRAN will retry with delays

8. Block Size Handling

Critical for proper operation:

// After INQUIRY, device must report:
// - For disks: Use READ CAPACITY(10) to return:
//   * Last block address (total blocks - 1)
//   * Block size in bytes (typically 512 or 1024)
//
// - For tapes: Use READ BLOCK LIMITS to return:
//   * Maximum block length
//   * Minimum block length
//   * If max == min: Fixed block mode
//   * If different: Variable block mode

public class DeviceGeometry
{
    public uint TotalBlocks;
    public uint BlockSize;
    public bool FixedBlockMode;
}

SINTRAN uses block size for: - Calculating DMA transfer lengths - Converting between logical records and physical blocks - Validating transfer requests

Testing Checklist

Basic Commands

  • [ ] TEST UNIT READY returns GOOD status
  • [ ] INQUIRY returns valid device type
  • [ ] READ CAPACITY returns correct disk size
  • [ ] REQUEST SENSE returns extended sense data
  • [ ] READ(6) transfers data correctly
  • [ ] WRITE(6) accepts data correctly

Status Handling

  • [ ] GOOD status allows operation to complete
  • [ ] CHECK CONDITION triggers REQUEST SENSE
  • [ ] BUSY status causes retry with delay
  • [ ] RESERVATION CONFLICT returns proper error

Sense Keys

  • [ ] NO SENSE (0x00) = success
  • [ ] RECOVERED ERROR (0x01) = warning logged
  • [ ] NOT READY (0x02) = device not ready
  • [ ] MEDIUM ERROR (0x03) = data error
  • [ ] ILLEGAL REQUEST (0x05) = bad parameter
  • [ ] UNIT ATTENTION (0x06) = triggers re-INQUIRY
  • [ ] ABORTED COMMAND (0x0B) = triggers retry

Function 74 (Custom Commands)

  • [ ] Can send INQUIRY via Function 74
  • [ ] Can send TEST UNIT READY via Function 74
  • [ ] Can read INQUIRY response data
  • [ ] Invalid CDB returns ILLEGAL REQUEST
  • [ ] Works for both data-in and data-out commands

Interrupt Mode

  • [ ] Interrupts generated on phase changes
  • [ ] RSTAU bit 11 set on NCR interrupt
  • [ ] Level 11 interrupt triggered
  • [ ] Operation pauses on WCONT=0
  • [ ] Operation resumes on WCONT=5

Advanced

  • [ ] MODE SENSE returns device parameters
  • [ ] MODE SELECT changes device parameters
  • [ ] VERIFY command works
  • [ ] SEEK improves performance (optional)
  • [ ] RESERVE/RELEASE work for multi-host (optional)

Conclusion

SINTRAN III has comprehensive SCSI support including:

  1. ✅ All essential SCSI-2 commands for disks and tapes
  2. ✅ Automatic command sequences (INQUIRY→READ CAPACITY)
  3. ✅ Full error handling with proper sense key interpretation
  4. ✅ User-accessible custom commands via Function 74
  5. ✅ INQUIRY command support both built-in (Function 75) and custom (Function 74)

Applications CAN: - Send INQUIRY commands using Function 74 (custom CDB) - Send INQUIRY commands using Function 75 (automatic parsing) - Send ANY valid SCSI command via Function 74 - Read complete response data - Parse device information

For C# Emulator: - Implement all commands in SCSF1/SCSF2 arrays - Return proper extended sense data on CHECK CONDITION - Support Function 74 for custom CDB execution - Handle UNIT ATTENTION (sense key 6) correctly - triggers re-initialization - Generate interrupts on all SCSI phase changes (see previous guide)

Document Path: Source Code\Sintran L\NPL\SCSI-Commands-Analysis.md