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IP-P2-SCSI-DISK - SCSI Disk Subsystem Documentation

File: IP-P2-SCSI-DISK.NPL

Purpose: SCSI Disk, Tape and Controller Drivers for ND-100

Table of Contents

  1. Overview
  2. Complete Function Reference
  3. Operation Type Control Words
  4. Status Mapping
  5. Elevator Algorithm (DSORT)
  6. Data Structures
  7. Error Handling
  8. Mermaid Diagrams

1. Overview

The IP-P2-SCSI-DISK module contains three driver subsystems for SCSI devices:

1.1 CTRSCSI - SCSI Controller Driver

Lines: 80-122

Purpose: Generic SCSI controller interface driver

Entry Point: CTRSCSI (line 90)

Activation: B=Datafield, X=Abstract parameter list

Key Features: - General-purpose SCSI command dispatcher - Translates high-level commands to SCSI driver calls - Supports all SCSI device types - Function code 21 (Clear SCSI Bus) special handling

1.2 SCSDISK - SCSI Disk Driver

Lines: 154-426

Purpose: SCSI disk operations with advanced features

Entry Point: SCSDISK (line 250)

Key Features: - Disk-specific operations (read, write, seek, format) - Partition management with access control - Elevator algorithm (SCAN/CSCAN disk scheduling) - Inquiry and capacity detection - Error logging and retry logic

1.3 SCSTREAM - SCSI Tape Streamer Driver

Lines: 505-1045

Purpose: SCSI tape operations

Entry Point: SCSTREAM (line 578)

Key Features: - Tape-specific operations (rewind, skip, erase) - Variable and fixed block modes - Density selection - Copy operations between tape and disk - Error counters for read/write operations

2. Complete Function Reference

2.1 CTRSCSI Functions (Lines 13-47)

Code Function Description
0 READ Read data from device
1 WRITE Write data to device
2 READ PARITY Read with parity check
3 COMPARE Compare data
4 SEEK Position head
5 READ BACKWARDS Read in reverse
6 RESERVE DEVICE Reserve device for exclusive use
10 ADVANCE THROUGH EOF Skip forward past EOF marker
11 REVERSE THROUGH EOF Skip backward past EOF marker
12 WRITE EOF Write end-of-file marker
13 REWIND Rewind tape to beginning
14 WRITE SKIP Skip and write
15 REVERSE RECORDS Move backward N records
16 ADVANCE RECORDS Move forward N records
17 UNLOAD Eject/unload media
21 CLEAR SCSI BUS Reset SCSI bus
26 READ BYTE RECORD Read byte-oriented record
27 WRITE BYTE RECORD Write byte-oriented record
30 LOAD Load media
35 RELEASE DEVICE Release device reservation
37 READ EXTENDED STATUS Get detailed error information
41 FORMAT Format media
42 INQUIRY AND READ CAPACITY Query device capabilities
46 READ CURRENT ADDRESS Get current position
47 WRITE CURRENT ADDRESS Set current position
54 COPY Copy data between devices
70 RETENSION Retension tape
71 WRITE AND VERIFY Write with verification
73 TEST UNIT READY Check device ready status
74 EXECUTE USER SPECIFIED SCSI COMMAND BLOCK Execute raw SCSI command
75 INQUIRY (READ DEVICE TYPE) Query device type
76 ADVANCE TO END OF RECORDED AREA Seek to end of data

2.2 SCSDISK Functions (Lines 130-152)

Code Function Description
0 READ Read sectors from disk
1 WRITE Write sectors to disk
2 READ PARITY Read with parity verification
3 COMPARE Compare disk data with memory
4 SEEK Position disk head
6 PRIORITY SELECT (DUMMY) No operation (placeholder)
34 RESERVE DEVICE Reserve disk for exclusive access
35 RELEASE DEVICE Release disk reservation
36 READ DISK LAYOUT RECORD Get disk geometry/partition info
37 READ EXTENDED STATUS Get SCSI sense information
41 FORMAT Format disk
42 READ FORMAT Query disk format parameters
43 READ IN CONTROL AREA Read from control/partition area
44 WRITE IN CONTROL AREA Write to control/partition area
60 READ (DOUBLE DISK ADDRESS) Read using 32-bit address
61 WRITE (DOUBLE DISK ADDRESS) Write using 32-bit address
62 READ PARITY (DOUBLE DISK ADDRESS) Read parity with 32-bit address
63 COMPARE (DOUBLE DISK ADDRESS) Compare with 32-bit address
73 TEST UNIT READY Check disk ready status
74 EXECUTE USER SPECIFIED SCSI COMMAND BLOCK Execute raw SCSI command
75 INQUIRY (READ DEVICE TYPE) Query device type and geometry

2.3 SCSTREAM Functions (Lines 475-503)

Code Function Description
0 READ Read from tape
1 WRITE Write to tape
2 READ PARITY Read with parity check
3 COMPARE Compare tape data
7 ERASE Erase tape
10 ADVANCE THROUGH EOF Skip forward past EOF
12 WRITE EOF Write end-of-file marker
13 REWIND Rewind tape
16 ADVANCE RECORDS Move forward N records
17 UNLOAD Unload tape
20 READ STATUS (TEST UNIT READY) Check tape status
23 SELECT DENSITY Set tape density
24 READ LAST STATUS Return cached status
25 READ TAPE STATUS (ERROR COUNTERS) Get error statistics
30 LOAD Load tape
31 RESET DEVICE (BUS DEVICE RESET) Reset tape unit
34 RESERVE DEVICE Reserve tape
35 RELEASE DEVICE Release tape reservation
37 READ EXTENDED STATUS Get extended error info
42 READ FORMAT Query tape format
46 RETURN INTERFACE TYPE Returns 3 for SCSI streamer
54 COPY Copy between tape and disk
70 RETENSION Retension tape
73 TEST UNIT READY Check tape ready
74 EXECUTE USER SPECIFIED SCSI COMMAND BLOCK Execute raw SCSI command
75 INQUIRY (READ DEVICE TYPE) Query tape type
76 ADVANCE TO END OF RECORDED AREA Seek to EOD

3. Operation Type Control Words

3.1 SCSDISK OPTYP Array (Lines 237-246)

The OPTYP array contains control words for each function code. Each word uses bit flags to control operation behavior:

Flag Bits (Lines 160-167):

Bit Symbol Meaning
17 3SERR Error message - log errors to system
16 3SNTR Neutral operation - don't modify status
15 3DPA3 Parameter 3 is double word
14 3DPA2 Parameter 2 is double word
13 3SPES Special operation - not sorted in queue
12 3PART Partition access - validate boundaries
11 3WRIT Write operation
10 3SF42 Function 42 (special format inquiry)

OPTYP Values:

Index (Octal):  Value (Octal)  Binary Flags         Operations
00-07:          100004         3PART + sortable     READ
                101004         3PART+3WRIT          WRITE
                100004         3PART                READ PARITY
                100004         3PART                COMPARE
                110004         3PART+3SPES          SEEK (special)
                000000         (illegal)
                104004         3PART+3SNTR          PRIORITY SELECT
                000000         (illegal)

34-37:          104017         3SNTR+3SPES          RESERVE DEVICE
                104404         3SNTR+3SPES          RELEASE DEVICE
                012004         3DPA2+3PART          READ DISK LAYOUT
                013004         3DPA2+3DPA3+3PART    READ EXTENDED STATUS

40-47:          (Function 41-42: Format operations)
                044000         3SPES+3SF42          READ FORMAT
                044000         3SPES+3SF42          (Function 42)

60-67:          110004         3SPES+3DPA2+3PART    READ (double addr)
                111004         ALL flags            WRITE (double addr)
                110004         3SPES+3DPA2+3PART    READ PARITY (double)
                110004         3SPES+3DPA2+3PART    COMPARE (double)

3.2 SCSTREAM OPTYP Array (Lines 568-577)

SCSTREAM Flag Bits (Lines 532-538):

Bit Symbol Meaning
15 9SAMT Fixed amount (bits 16-17)
14 9SSWA Single word amount
13 9SRRA Return resulting amount to user
12 9SCRS Clear pending rewind error status
11 9SRUA Remove unit attention
10 9SIUA Ignore unit attention
7 9SSPC Special command

4. Status Mapping

4.1 SCSDISK NEWST Array (Lines 181-184)

Maps SCSI sense keys (0-15) to SINTRAN error bits:

Sense Key    Value (Octal)  Meaning
0:           040000         No sense (bit 14 set)
1:           040000         Recovered error (bit 14)
2:           100020         Not ready (bit 15 + bit 4)
3:           140020         Medium error (bits 14,15,4)
4:           140220         Hardware error (bits 14,15,7,4)
5:           140020         Illegal request (bits 14,15,4)
6:           140020         Unit attention (bits 14,15,4)
7:           040020         Data protect (bits 14,4)
8:           040020         Blank check (bits 14,4)
9:           140020         Vendor specific (bits 14,15,4)
10:          150020         Copy aborted (bits 14,16,4)
11:          140020         Aborted command (bits 14,15,4)
12:          040000         Equal (comparison) (bit 14)
13:          140020         Volume overflow (bits 14,15,4)
14:          042020         Miscompare (bits 14,10,4)
15:          140020         Reserved (bits 14,15,4)

4.2 SCSTREAM NEWST Array (Lines 308-311)

Similar mapping for tape operations with additional tape-specific flags:

Sense Key    Value (Octal)  Meaning
0:           000400         Good status (bit 10)
1:           000400         Recovered error (bit 10)
2:           000020         Not ready (bit 4)
3:           100420         Medium error (bits 15,10,4)
4:           000020         Hardware error (bit 4)
5:           000020         Illegal request (bit 4)
6:           000020         Unit attention (bit 4)
7:           000020         Data protect (bit 4)
8:           100420         Blank check/EOM (bits 15,10,4)
9:           000020         Vendor specific (bit 4)
10:          000020         Copy aborted (bit 4)
11:          000020         Aborted command (bit 4)
12:          000020         Equal (bit 4)
13:          100420         Volume overflow (bits 15,10,4)
14:          100420         Miscompare (bits 15,10,4)
15:          000020         Reserved (bit 4)

4.3 CTRSCSI NEWST Array (Lines 85-87)

Simplified mapping for generic controller:

All sense keys: 000000 or 000020 (bit 4 for errors)

5. Elevator Algorithm (DSORT)

File: IP-P2-DISK-START.NPL (Lines 270-319)

Purpose: Optimize disk I/O by sorting requests in a direction that minimizes head movement

5.1 Algorithm Description

The DSORT routine implements the SCAN (elevator) algorithm:

  1. Current Direction: Maintain movement direction (increasing or decreasing addresses)
  2. Service Requests: Process all requests in current direction
  3. Reverse at End: When no more requests exist in current direction, reverse
  4. Minimize Seeks: Reduces total seek time by avoiding random access

5.2 Key Data Structures

Queue Pointers: - SCLINK - Queue head (sorted requests) - NLINK - Next element in queue - PLHAD - Last processed in current direction - PLELE - Last element in queue - CHADD - Current head address (physical position)

Direction Control: - MOVME - Movement direction flag (0=decreasing, 1=increasing) - SSEEK - Seek enable bit in TYPCO

5.3 DSORT Algorithm Flow

Entry: X = Unit datafield, B = Queue element datafield

1. Initialize pointers:
   PREVQ = pointer before first element
   LASTQ = pointer before first in opposite direction

2. Determine insertion direction:
   - Compare new request address with CHADD (current head address)
   - XOR with MOVME to determine if direction change needed

3. Scan queue in current direction:
   IF increasing (MOVME bit set):
      - Find first element > new request address
   ELSE decreasing:
      - Find first element < new request address

4. Insert request:
   - Link new element after PREVQ
   - Update PLHAD if inserted at direction boundary
   - Update PLELE if last element

5. Direction reversal (in RETEX, lines 413-425):
   - When SCLINK exhausted and PLHAD = current
   - Set PLHAD = PLELE (restart from other end)
   - Toggle MOVME direction bit

5.4 Partition Validation (Lines 278-300)

For partition access (3PART bit set):

  1. Extract partition index from address (bits in ABP21)
  2. Validate partition index < NPART
  3. Load partition control word from CMAD buffer
  4. Check read/write access bits (bits 15-16)
  5. Add partition base address to request address
  6. Verify request + amount within partition boundaries

5.5 Example Scenario

Initial state:
  CHADD = 1000 (current head at cylinder 1000)
  MOVME = 1 (moving toward higher addresses)
  Queue: Empty

Request sequence:
  1. Request at 1500 -> Insert, continue upward
  2. Request at 800  -> Insert before first (will process after reversal)
  3. Request at 2000 -> Insert after 1500
  4. Request at 1200 -> Insert between 1000 and 1500

Sorted queue (upward pass):
  1200 -> 1500 -> 2000

After reaching 2000:
  - Reverse direction (MOVME = 0)
  - PLHAD = PLELE
  - Process downward: 800

6. Data Structures

6.1 Abstract Parameter Block (ABSTR)

Common Fields:

Offset Field Type Description
+0 ABFUN INT Function code (bits 0-5) + Unit (bits 6-8)
+1 MEMAD INT Memory address (word address)
+2 ABPA2 DOUBLE Parameter 2 (disk address/tape position)
+4 ABPA3 DOUBLE Parameter 3 (amount/sector count)

Extended Fields (Function-specific):

Field Type Description
ABP21 INT Lower word of ABPA2 (single-word address)
ABP22 INT Upper word of ABPA2
ABP31 INT Lower word of ABPA3
ABP32 INT Upper word of ABPA3
ABA31 INT Alternate parameter 3 reference
ABA32 INT Alternate parameter 3 reference
MEMA1 INT Memory address reference
MEMA2 INT Memory address reference

6.2 Unit Datafield (LUN Structure)

SCSDISK Fields:

Field Description
SUTYP Device type and flags (5SCIN, 5SCDA, etc.)
SCDFA Device datafield address
SCOCW Operation control word
CHADD Current head address (physical)
NPART Number of partitions
CMAD1/CMAD2 Control area address
UHLIM Upper disk limit (double word)
ULINK Unit link pointer
SLINK Started operations queue
SCLINK Sorted queue head
NLINK Next in queue
PLHAD Last processed in direction
PLELE Last element in queue
MOVME Movement direction
SUNOP Number of operations in queue
TYPCO Type control (with SSEEK bit)
STPRW Program owning access
TACNS Retry count (total attempts)
TACOU Retry counter (current)

SCSTREAM Additional Fields:

Field Description
OPSTA Operation status flags (4SRUN, 4SSTA, 4SRES, 4SINI, 4SMSL, 4SSTP, 4SUAP)
CUROP Current operation control word
STSTA Status from last operation
P3LUN Parameter 3 LUN reference
CFORM Current format/density
REWST Rewind status (pending)
SRERS Read error status accumulator
SRERC Read error counter
SWERS Write error status accumulator
SWERC Write error counter
CPFUN Copy function
CPDEV Copy device
CPSTS Copy status
CPBLS Copy block size
CPAMT Copy amount transferred

6.3 Partition Control Record (Function 42)

Structure (6 words per partition):

Offset Field Description
+0 Access bits Bit 15: Write access, Bit 16: Read access
+1 (reserved)
+2 Lower limit Lower address (word 1 of double)
+3 Lower limit Lower address (word 2 of double)
+4 Length Partition length (word 1 of double)
+5 Length Partition length (word 2 of double)

Validation (Lines 278-300): 1. Check partition index in bits 10-15 of ABP21 2. Verify index < NPART 3. Check access bit (read=16, write=15) 4. Add lower limit to request address 5. Verify (address + amount) <= (lower limit + length)

7. Error Handling

7.1 RETOP - Disk Termination (Lines 194-231)

Purpose: Terminate disk operation and report status

Entry Parameters: - B = Disk datafield - X = DAQ (Device Adapter Queue) - T = Driver status (0 = success) - A = Sense key (if T=0)

Status Processing:

  1. Update error bits from NEWST array (lines 196-205)
  2. Check for error flag in HSTAT bit 4 (line 207)
  3. Log error if 3SERR bit set (lines 211-221):
    • Call PHLOG to get device number
    • Extract unit from ABFUN
    • Collect parameters (memory address, disk address, amount)
    • Call 9FLEX(1663, 12) to report error
  4. Return original status if 3SNTR set (lines 224-226)
  5. Return to caller via TO11Q (line 228)

7.2 SCSTREAM Error Handling

RETOP Sequence (Lines 301-385):

  1. Check for copy operation termination (lines 317-322)
  2. Map sense key to error bits (lines 323-330):
    • ILI (Incorrect Length Indicator) -> 100420
    • EOM (End of Media) -> 000420
    • EOF (End of File) -> 100420
  3. Adjust amount for residual (lines 331-351):
    • Use shift instructions (SUSI1, SUSI2)
    • Calculate physical vs logical record size
    • Return adjusted amount to user
  4. Handle special operations (lines 359-368):
    • Reserve device (34) -> set 4SRES bit
    • Release device (35) -> clear 4SRES bit
  5. Determine SINTRAN error code (line 371):
    • Call SCDTS to map to SINTRAN error numbers

7.3 Error Code Mapping (SCDTS, Lines 582-618)

Driver Error Codes to SINTRAN:

Driver Code SINTRAN Code Meaning
TYPER 240 Illegal device type
ILAOP 201 Illegal function code
BADPA 174 Illegal parameter
ILNOD 33 No such logical unit
NOLUN 33 No such logical unit
COPNP 3206 Illegal request (copy not possible)
TRANE 141 Transfer error
SBUSY 3207 Device busy
RCONF 3210 Reservation conflict
NESER 3211 Device does not answer
(other) 232 Device error

SCSI Sense Keys (from SCSTA array):

The driver maintains a SCSTA array that maps SCSI sense keys (0-15) to SINTRAN error codes. When T=0 and CERRCODE=0, the sense key is used to index this array.

7.4 Retry Logic

SCSDISK Retry (Lines 345-382):

  1. Check retry counter (line 343): TACNS -> TACOU
  2. Auto-inquiry if needed (lines 346-361):
    • If SUTYP lacks 5SCIN bit, run inquiry
    • If device type invalid, error TYPER
  3. Call SCSID driver (line 373)
  4. Check for recoverable errors (lines 380-382):
    • PFAIL (power fail) -> retry
    • SBRST (SCSI bus reset) -> retry
    • LIRST (local interface reset) -> retry
    • Decrement TACOU and retry

SCSTREAM Retry (Lines 214-291):

  1. Check for unit attention (lines 214-220):
    • If 4SUAP bit set and not ignored (9SIUA)
    • Return error 26 if not removable (9SRUA)
  2. Initialization sequence (lines 222-231):
    • Reserve/Release device (34/36)
    • Call SCSID, check sense
    • Verify device type = 1 (sequential access)
  3. Mode Select for streamers (lines 232-246):
    • Execute Mode Sense (MDSEN)
    • Get density (GDENS)
    • Execute Mode Select (MDSEL)
    • Verify fixed block mode (5SFBM)
  4. Error analysis (lines 269-294):
    • Unit attention (6) -> set 4SUAP, retry
    • Copy aborted (12) -> analyze copy status
    • Aborted command (13) -> retry
    • Recovered error (1) or medium error (3) -> increment error counters

7.5 Function 42 Special Handling (Lines 337-407)

Purpose: Read and validate partition/format information

Process:

  1. Clear SUTYP 5SCIN bit (line 340) to force inquiry
  2. Execute inquiry (lines 346-361) to get device geometry
  3. Read control record (lines 362-367):
    • Address from MEMA1/MEMA2 + 10 (offset)
    • Read 1 sector to memory address + 1000
  4. Validate control record (lines 387-407):
    • Clear cache (SCCLR)
    • Read first word at MEMAD offset 0
    • Calculate checksum (XOR all words)
    • Extract NPART from high byte
    • Verify checksum = 0
    • Verify 2 <= NPART <= NCOPA (max partitions)
  5. Copy partition table (lines 400-402):
    • Move NPART*6 words to CMAD1/CMAD2 buffer
  6. Return disk capacity (lines 402-404):
    • Store UHLIM at MEMA1/MEMA2 + 10

8. Mermaid Diagrams

8.1 Disk Operation Dispatcher Flow

graph TD
    A[SCSDISK Entry] --> B{Check OPTYP}
    B -->|Invalid| C[ILAOP Error]
    B -->|Valid| D{Convert Parameters}
    D --> E{Double Address?}
    E -->|Yes 3DPA2| F[Convert ABP21 to ABPA2]
    E -->|No| G{Double Amount?}
    G -->|Yes 3DPA3| H[Convert ABP32 to ABPA3]
    G -->|No| I{Get LUN DF}
    H --> I
    F --> G
    I -->|Failed| J[NOLUN Error]
    I -->|Success| K{Partition Access?}
    K -->|Yes 3PART| L[Validate Partition]
    K -->|No| M[Validate Disk Limits]
    L -->|Failed| N[BADPA Error]
    L -->|Success| O{Special Operation?}
    M -->|Failed| N
    M -->|Success| O
    O -->|Yes 3SPES| P[Execute Special]
    O -->|No| Q{Queue Empty?}
    Q -->|Yes| R[NEWOP: Start Operation]
    Q -->|No| S[DSORT: Sort into Queue]
    S --> T[SWT11: Return to Scheduler]
    P --> T
    R --> U{Function Type}
    U -->|6| V[Dummy Return]
    U -->|36| W[Read Disk Layout]
    U -->|42| X[Read Format Info]
    U -->|Other| Y[Call SCSID Driver]
    V --> T
    W --> T
    X --> Z[Auto-Inquiry if Needed]
    Z --> AA[Read Control Record]
    AA --> AB[Validate Checksum]
    AB --> T
    Y --> AC[RETRY Loop]
    AC --> AD{Success?}
    AD -->|Yes| AE[FINEX: Process Results]
    AD -->|No| AF{Recoverable?}
    AF -->|Yes| AC
    AF -->|No| AG[ERREX: Report Error]
    AE --> AH[RETEX: Terminate & Cleanup]
    AG --> AH
    AH --> T
    C --> T
    J --> T
    N --> T

8.2 Queue Sorting Algorithm (Elevator/SCAN)

graph TD
    A[DSORT Entry<br/>X=Unit DF, B=Request DF] --> B[Save PREVQ = SCLINK]
    B --> C{PLHAD == 0?}
    C -->|Yes| D[LASTQ = PREVQ]
    C -->|No| E[LASTQ = PLHAD]
    D --> F{TYPCO has SSEEK?}
    E --> F
    F -->|No| G{PLELE != 0?}
    F -->|Yes| H[Compare Request vs CHADD]
    H --> I{Direction Change?}
    I -->|Yes XOR MOVME| J[Toggle MOVME Direction]
    I -->|No| K[Load MOVME to K]
    J --> L{Queue Empty?}
    L -->|Yes| M[Initialize MOVME]
    L -->|No| N[LASTQ = PREVQ, Reset LASTQ]
    M --> K
    N --> K
    K --> O[Start Queue Scan]
    O --> P{Current == LASTQ?}
    P -->|Yes| Q[Toggle Direction in K]
    P -->|No| R{More Elements?}
    Q --> R
    R -->|No| S[End Scan]
    R -->|Yes| T{Has SSEEK?}
    T -->|No| U[PREVQ = Current]
    T -->|Yes| V{K Direction?}
    V -->|Increasing| W[Compare Request vs Current End]
    V -->|Decreasing| X[Compare Current vs Request End]
    W --> Y{Request > Current?}
    X --> Z{Current > Request?}
    Y -->|No| U
    Y -->|Yes| AA[PREVQ = Current]
    Z -->|No| U
    Z -->|Yes| AA
    AA --> R
    U --> R
    S --> AB[Insert After PREVQ]
    AB --> AC{Inserted at LASTQ?}
    AC -->|Yes| AD[Update PLHAD]
    AC -->|No| AE{NLINK == 0?}
    AD --> AE
    AE -->|Yes| AF[Update PLELE]
    AE -->|No| AG[Return]
    AF --> AG
    G -->|Yes| AH[Insert After PLELE]
    G -->|No| AI[Insert at Head]
    AH --> AG
    AI --> AG

    style J fill:#ffcccc
    style Q fill:#ffcccc
    style AB fill:#ccffcc

8.3 Partition Validation Flow

graph TD
    A[Partition Access<br/>3PART bit set] --> B[Extract Original Address]
    B --> C[Get Partition Index<br/>ABP21 bits 10-15]
    C --> D{Index < NPART?}
    D -->|No| E[BADPA Error]
    D -->|Yes| F[Calculate Partition Offset<br/>Index * 6]
    F --> G[Load Partition Control Word<br/>from CMAD1/CMAD2]
    G --> H{Operation Type?}
    H -->|Write 3WRIT| I{Write Access?<br/>Bit 15 set}
    H -->|Read| J{Read Access?<br/>Bit 16 set}
    I -->|No| E
    I -->|Yes| K[Load Partition Length<br/>CMAD + offset + 40]
    J -->|No| E
    J -->|Yes| K
    K --> L[Load Lower Limit<br/>CMAD + offset + 20]
    L --> M[Add Lower Limit to Request Address<br/>ABPA2 += Lower Limit]
    M --> N[Calculate End Address<br/>ABPA2 + ABP32]
    N --> O[Compare vs Partition Upper Limit<br/>Lower Limit + Length]
    O --> P{Within Bounds?}
    P -->|No| E
    P -->|Yes| Q[Update ABPA2 with Actual Address]
    Q --> R[Proceed with Operation]

    style E fill:#ffcccc
    style R fill:#ccffcc

8.4 Error Recovery and Retry Logic

graph TD
    A[Operation Failed<br/>A=Sense Key, T=Driver Status] --> B{T == 0?}
    B -->|No| C[Serious Driver Error<br/>T SHZ 11 -> Status]
    B -->|Yes| D{Check Sense Key}
    D -->|0-1| E[Update NEWST Array<br/>No error / Recovered]
    D -->|2-15| F[Map via NEWST Array]
    E --> G{HSTAT Bit 4?}
    F --> G
    C --> H{3SERR Bit Set?}
    G -->|Yes Error| H
    G -->|No| I[Return to Caller]
    H -->|Yes| J[Collect Error Info:<br/>Device, Unit, Address, Amount]
    H -->|No| K{3SNTR Bit Set?}
    J --> L[Call PHLOG for Device Number]
    L --> M[Call 9FLEX 1663,12<br/>Report Error]
    M --> K
    K -->|Yes| N[Return Original SCOSS Status]
    K -->|No| O{Check Recoverable}
    N --> I
    O --> P{PFAIL or SBRST or LIRST?}
    P -->|Yes| Q[Decrement TACOU]
    P -->|No| R[Return Error to Caller]
    Q --> S{TACOU > 0?}
    S -->|Yes| T[RETRY: Execute Operation Again]
    S -->|No| R
    T --> U{Need Inquiry?}
    U -->|Yes SUTYP lacks 5SCIN| V[Execute Function 36 or 42<br/>Auto-Inquiry]
    U -->|No| W[Call SCSID Driver]
    V --> X{Inquiry Success?}
    X -->|No| R
    X -->|Yes| Y{Valid Device Type?}
    Y -->|No| Z[TYPER Error]
    Y -->|Yes| W
    W --> AA{Result?}
    AA -->|Sense 6 or 13| Q
    AA -->|Other| AB[Return New Status]
    Z --> R
    AB --> I
    I --> AC[Call TO11Q<br/>Return to Level 11 Queue]

    style R fill:#ffcccc
    style AC fill:#ccffcc
    style T fill:#ffffcc

8.5 RETOP Termination Sequence

graph TD
    A[RETOP Entry<br/>B=Disk DF, X=DAQ<br/>T=Driver Status, A=Sense] --> B[Save TAD, X, L<br/>to SVTAD, SVXRG, SVLRG]
    B --> C[Save Original SCSI Status<br/>A -> SCOSS, L]
    C --> D{T == 0<br/>Success?}
    D -->|Yes| E{Function 2 or 62<br/>Compare?}
    D -->|No| F[T SHZ 11 -> L<br/>Serious Error 100020]
    E -->|Yes| G{Sense Key 5<br/>Not Implemented?}
    E -->|No| H[Map via NEWST Array<br/>X = 17/\L]
    G -->|Yes| I[Clear L<br/>L := 0]
    G -->|No| H
    I --> H
    H --> J[Update Error Bits<br/>NEWST X \/X -> Status]
    J --> K{HSTAT Bit 4 Set?}
    F --> K
    K -->|Yes Error| L[L BONE 4<br/>Set Error Flag]
    K -->|No| M{3SNTR Bit Set?}
    L --> N[Update SCOSS and XSTAT<br/>T=L=SCOSS=X.XSTAT]
    N --> O[Save ABFUN to DMTRG<br/>T=X.ABFUN=X.DMTRG]
    O --> P{A<0 AND 3SERR?}
    P -->|Yes| Q[Collect Error Parameters]
    P -->|No| M
    Q --> R[A=B, CALL PHLOG<br/>A=9XDV Device Number]
    R --> S[Extract ABFUN -> 9XFU<br/>Unit -> 9XUN]
    S --> T[Copy Parameters:<br/>MEMAD->9XMA<br/>ABPA2->9XDA<br/>ABP32->9XTA]
    T --> U[SCOSS->9XST<br/>RTRES->Program ID]
    U --> V[Call 9FLEX 1663,12<br/>Report Error to Log]
    V --> M
    M -->|Yes| W[Return Original SCOSS<br/>SCOSS=X.HSTAT]
    M -->|No| X[Disable Interrupts<br/>*IOF]
    W --> X
    X --> Y[Call TO11Q<br/>Return to Level 11]
    Y --> Z[Enable Interrupts<br/>*ION]
    Z --> AA[Restore Registers<br/>SVTAD, SVXRG]
    AA --> AB[Return via SVLRG<br/>GO SVLRG]

    style AB fill:#ccffcc
    style V fill:#ffccaa

8.6 NEWOP Initialization Sequence

graph TD
    A[NEWOP Entry<br/>X=SLINK Queue Head<br/>B=Unit DF] --> B[Clear NLINK<br/>0=X.NLINK]
    B --> C[Set Access Owner<br/>X.RTRES=ULINK.STPRW]
    C --> D{3SPES Bit Set?<br/>Special Operation}
    D -->|No| E[Save Current Head Address<br/>X.ABPA2=CHADD]
    D -->|Yes| F{Function Code?}
    F -->|6| G[Dummy Function<br/>T=0, Return]
    F -->|36| H[Read Disk Layout]
    F -->|42| I[Read Format Info<br/>Function 42 Processing]
    F -->|Other| J[Copy MEMAD and ABFUN]
    E --> K[Initialize Retry Counter<br/>TACNS=TACOU]
    J --> K
    K --> L[Get SCSI Device Datafield<br/>X=SCDFA, B unchanged]
    L --> M[RETRY Loop Start]
    M --> N{SUTYP has 5SCIN?<br/>Initialized?}
    N -->|No AND Not 3SNTR| O{3SF42 Bit?<br/>Function 42}
    N -->|Yes| P{3SF42 Bit Set?}
    O -->|Yes| Q[Execute Function 42<br/>Auto-Inquiry]
    O -->|No| R[Execute Function 36<br/>Standard Inquiry]
    Q --> S{Inquiry Loop}
    R --> S
    S --> T[Call SCSID Driver<br/>T=X]
    T --> U{Result?}
    U -->|Sense 6 or 13| V[Decrement TACOU<br/>Unit Attention/Aborted]
    U -->|Success D<=1| W{Valid Device Type?}
    U -->|Other Error| X[GO FAR ERREX]
    V --> S
    W -->|No SUTYP SHZ -10=0| Y[TYPER Error]
    W -->|Yes| P
    Y --> X
    P -->|Yes| Z[Read Control Record]
    P -->|No| AA[Determine Parameter Pointer<br/>T=X.SLINK or X]
    Z --> AB[Setup for READ:<br/>177700/\ABFUN, MEMA2+10]
    AB --> AC[Read 1 Sector at MEMAD+1000]
    AC --> AA
    AA --> AD[Call SCSID Driver<br/>377/\SCOCW control]
    AD --> AE{Result?}
    AE -->|Sense 6 or 13| AF[Decrement TACOU]
    AE -->|Success| AG[GO FINEX]
    AE -->|Error| X
    AF --> M
    AG --> AH[Process Function 42 Results]
    AH --> AI[Clear Cache<br/>SCCLR]
    AI --> AJ[Read First Word<br/>MEMAD offset 0]
    AJ --> AK[Extract NPART<br/>A SHZ -10]
    AK --> AL[Calculate Checksum<br/>XOR all words]
    AL --> AM{Valid Checksum<br/>AND NPART Range?}
    AM -->|No| AN[NOCRC Error]
    AM -->|Yes| AO[Copy Partition Table<br/>NPART*6 words to CMAD]
    AO --> AP[Return Data Area Size<br/>Store at MEMA2+10]
    AP --> AQ[Store UHLIM<br/>36, offset 0]
    AQ --> AR[RETEX: Terminate]
    H --> AS[Check Index <= MAXDI<br/>AND DISPE X valid]
    AS --> AT{Valid?}
    AT -->|Yes| AU[Copy 11 words<br/>DISPE to MEMA1/MEMA2]
    AT -->|No| AV[BADPA Error]
    AU --> AR
    AV --> AR
    G --> AR
    AN --> AR
    X --> AR

    style AR fill:#ccffcc
    style G fill:#ccccff
    style AN fill:#ffcccc
    style Y fill:#ffcccc
    style AV fill:#ffcccc

8.7 Complete Read Operation

graph TD
    A[User Calls SCSDISK<br/>Function 0 READ] --> B[SCSDISK Entry<br/>Save Return Address]
    B --> C[Fetch ABFUN<br/>Extract Function 0-77 octal]
    C --> D[Lookup OPTYP Array<br/>OPTYP 0 = 100004]
    D --> E{OPTYP == 0?}
    E -->|Yes| F[ILAOP Error]
    E -->|No| G[Check 3DPA2 Bit 14<br/>Double Address?]
    G -->|Yes| H[Convert ABP21 to Double<br/>X.ABPA2 = 0, ABP21]
    G -->|No| I[Check 3DPA3 Bit 15<br/>Double Amount?]
    H --> I
    I -->|Yes| J[Convert ABP31 to Double<br/>X.ABPA3 = 0, ABP32]
    I -->|No| K[Extract Unit from ABFUN<br/>Bits 6-8, SHZ -6/\7]
    J --> K
    K --> L{Unit > 3 OR<br/>PUNDF A == 0?}
    L -->|Yes| M[NOLUN Error]
    L -->|No| N[X=B=SAVEX<br/>Save Unit DF]
    N --> O{3SPES Bit 13?<br/>Special Operation}
    O -->|Yes| P[Execute Special<br/>Functions 6,36,42]
    O -->|No| Q{3PART Bit 12?<br/>Partition Access}
    Q -->|Yes| R[Validate Partition<br/>See Partition Flow]
    Q -->|No| S[Validate Disk Limits<br/>ABPA2+ABP32 vs UHLIM]
    R --> T{Valid?}
    S --> T
    T -->|No| U[BADPA Error]
    T -->|Yes| V[Set SSEEK Bit<br/>X.TYPCO BONE SSEEK]
    V --> W[Increment SUNOP<br/>MIN SUNOP, 0/\0]
    W --> X{SLINK != 0?<br/>Queue Not Empty}
    X -->|Yes| Y[Call DSORT<br/>Sort into Queue]
    X -->|No| Z[GO NEWOP<br/>Start Immediately]
    Y --> AA[Return to Scheduler<br/>GO SWT11]
    Z --> AB[NEWOP: X=SLINK<br/>0=X.NLINK]
    AB --> AC[Set Access Owner<br/>X.RTRES=ULINK.STPRW]
    AC --> AD[Save Current Head<br/>X.ABPA2=CHADD]
    AD --> AE[Initialize Retry<br/>TACNS=TACOU]
    AE --> AF[Get Device DF<br/>X=SCDFA=B]
    AF --> AG[RETRY Loop]
    AG --> AH{SUTYP has 5SCIN?}
    AH -->|No| AI[Auto-Inquiry<br/>Function 36/42]
    AH -->|Yes| AJ[Build SCSI Command<br/>Via SCSID]
    AI --> AK{Inquiry OK?}
    AK -->|No| AL[TYPER Error]
    AK -->|Yes| AJ
    AJ --> AM[Call SCSID Driver<br/>READ Command]
    AM --> AN{Result?}
    AN -->|Error| AO{Recoverable?}
    AN -->|Success| AP[GO FINEX]
    AO -->|PFAIL/SBRST/LIRST| AQ[Decrement TACOU]
    AO -->|No| AR[GO ERREX]
    AQ --> AS{TACOU > 0?}
    AS -->|Yes| AG
    AS -->|No| AR
    AP --> AT[X=B=SLINK<br/>Process Results]
    AT --> AU[Update Status<br/>T=0 Success]
    AU --> AV[RETEX: B=D<br/>X=ULINK=B=X.SLINK]
    AV --> AW[Clear STPRW<br/>0=STPRW]
    AW --> AX[Call RETOP<br/>Terminate Operation]
    AX --> AY[Clear SLINK<br/>0=SLINK]
    AY --> AZ[Decrement SUNOP<br/>SUNOP-1=SUNOP]
    AZ --> BA{SCLINK != 0?<br/>More in Sorted Queue}
    BA -->|Yes| BB[Check if Last<br/>X.NLINK=SCLINK=0]
    BA -->|No| AA
    BB --> BC{Last Element?}
    BC -->|Yes| BD[Clear PLELE<br/>0=PLELE]
    BC -->|No| BE{PLHAD == X?}
    BD --> BE
    BE -->|Yes| BF[Clear PLHAD<br/>0=PLHAD]
    BE -->|No| BG{PLHAD == 0?}
    BF --> BG
    BG -->|Yes| BH[Reverse Direction<br/>PLELE=PLHAD<br/>MIN MOVME, 0/\0]
    BG -->|No| BI[GO FAR NEWOP<br/>Process Next]
    BH --> BI
    P --> AA
    F --> AA
    M --> AA
    U --> AA
    AL --> AA
    AR --> AA
    BI --> AA

    style A fill:#3F51B5,stroke:#303F9F,stroke-width:2px,color:#fff
    style AA fill:#4CAF50,stroke:#388E3C,stroke-width:2px,color:#fff
    style F fill:#F44336,stroke:#D32F2F,stroke-width:2px,color:#fff
    style M fill:#F44336,stroke:#D32F2F,stroke-width:2px,color:#fff
    style U fill:#F44336,stroke:#D32F2F,stroke-width:2px,color:#fff
    style AL fill:#F44336,stroke:#D32F2F,stroke-width:2px,color:#fff
    style AR fill:#F44336,stroke:#D32F2F,stroke-width:2px,color:#fff
    style AP fill:#4CAF50,stroke:#388E3C,stroke-width:2px,color:#fff
    style AM fill:#2196F3,stroke:#1976D2,stroke-width:2px,color:#fff
    style AJ fill:#2196F3,stroke:#1976D2,stroke-width:2px,color:#fff
    style AG fill:#FF9800,stroke:#F57C00,stroke-width:2px,color:#fff

8.8 Complete Write Operation

graph TD
    A[User Calls SCSDISK<br/>Function 1 WRITE] --> B[SCSDISK Entry<br/>Same as READ Start]
    B --> C[Lookup OPTYP Array<br/>OPTYP 1 = 101004]
    C --> D[Check 3WRIT Bit 11<br/>Write Operation Flag]
    D --> E{OPTYP Valid?}
    E -->|No| F[ILAOP Error]
    E -->|Yes| G[Convert Parameters<br/>Same as READ]
    G --> H{3PART Bit 12?<br/>Partition Access}
    H -->|Yes| I[Validate Partition<br/>Check Write Bit 15]
    H -->|No| J[Validate Disk Limits]
    I --> K{Write Access Allowed?}
    K -->|No| L[BADPA Error<br/>Not Write Access]
    K -->|Yes| M[Add Lower Limit<br/>Calculate Actual Address]
    J --> N{Within Bounds?}
    M --> O[Verify End Address<br/>vs Partition Limit]
    O --> N
    N -->|No| L
    N -->|Yes| P[Set SSEEK Bit<br/>Enable Sorting]
    P --> Q[Increment SUNOP<br/>Operation Count]
    Q --> R{SLINK != 0?}
    R -->|Yes| S[Call DSORT<br/>Insert in Elevator Queue]
    R -->|No| T[GO NEWOP<br/>Execute Immediately]
    S --> U[DSORT Sorts by Address]
    U --> V{Direction?}
    V -->|Increasing| W[Insert After Smaller Addresses]
    V -->|Decreasing| X[Insert After Larger Addresses]
    W --> Y[Update Queue Pointers<br/>NLINK, PLHAD, PLELE]
    X --> Y
    Y --> Z[Return to Scheduler<br/>GO SWT11]
    T --> AA[NEWOP: Set CHADD<br/>Current Head Address]
    AA --> AB[Initialize Retry<br/>TACNS=TACOU]
    AB --> AC[Get Device DF<br/>X=SCDFA=B]
    AC --> AD[RETRY Loop]
    AD --> AE{Device Initialized?}
    AE -->|No| AF[Auto-Inquiry]
    AE -->|Yes| AG[Build WRITE Command<br/>SCSI Function 12\340]
    AF --> AH{Inquiry Success?}
    AH -->|No| AI[TYPER Error]
    AH -->|Yes| AG
    AG --> AJ[Set Write Bit in Command<br/>Bit 0 of CTRG]
    AJ --> AK[Call SCSID Driver<br/>WRITE Command]
    AK --> AL{Result?}
    AL -->|Error| AM{Recoverable?}
    AL -->|Success| AN[GO FINEX]
    AM -->|PFAIL/SBRST| AO[Decrement TACOU]
    AM -->|Other| AP[GO ERREX]
    AO --> AQ{TACOU > 0?}
    AQ -->|Yes| AD
    AQ -->|No| AP
    AN --> AR[Process Results<br/>T=0 Success]
    AR --> AS[Call RETOP<br/>Terminate]
    AS --> AT{HSTAT Bit 4?<br/>Error Occurred}
    AT -->|Yes| AU[Check 3SERR Bit<br/>Log Error?]
    AT -->|No| AV[Update CHADD<br/>New Head Position]
    AU -->|Yes| AW[Call PHLOG<br/>Get Device Number]
    AU -->|No| AV
    AW --> AX[Collect Write Parameters<br/>ABFUN, MEMAD, ABPA2, ABP32]
    AX --> AY[Call 9FLEX 1663,12<br/>Report Write Error]
    AY --> AV
    AV --> AZ[Decrement SUNOP<br/>Operation Complete]
    AZ --> BA{SCLINK != 0?<br/>More Operations}
    BA -->|Yes| BB[Update Queue<br/>Remove Completed]
    BA -->|No| BC[Return to Scheduler<br/>GO SWT11]
    BB --> BD{Direction Change Needed?}
    BD -->|Yes| BE[Toggle MOVME<br/>Reverse Elevator]
    BD -->|No| BF[GO FAR NEWOP<br/>Process Next Write]
    BE --> BF
    BF --> AA
    F --> BC
    L --> BC
    AI --> BC
    AP --> BC

    style A fill:#3F51B5,stroke:#303F9F,stroke-width:2px,color:#fff
    style BC fill:#4CAF50,stroke:#388E3C,stroke-width:2px,color:#fff
    style F fill:#F44336,stroke:#D32F2F,stroke-width:2px,color:#fff
    style L fill:#F44336,stroke:#D32F2F,stroke-width:2px,color:#fff
    style AI fill:#F44336,stroke:#D32F2F,stroke-width:2px,color:#fff
    style AP fill:#F44336,stroke:#D32F2F,stroke-width:2px,color:#fff
    style AY fill:#FF9800,stroke:#F57C00,stroke-width:2px,color:#fff
    style AN fill:#4CAF50,stroke:#388E3C,stroke-width:2px,color:#fff
    style AK fill:#2196F3,stroke:#1976D2,stroke-width:2px,color:#fff
    style AG fill:#2196F3,stroke:#1976D2,stroke-width:2px,color:#fff
    style AD fill:#FF9800,stroke:#F57C00,stroke-width:2px,color:#fff
    style S fill:#9C27B0,stroke:#7B1FA2,stroke-width:2px,color:#fff

8.9 Function 42 (Format Info) Processing

graph TD
    A[Function 42 Request<br/>Read Format Info] --> B[SCSDISK Entry<br/>Extract Function 42]
    B --> C[Lookup OPTYP Array<br/>OPTYP 42 = 044000]
    C --> D[Check Flags:<br/>3SPES + 3SF42]
    D --> E{3SPES Set?}
    E -->|No| F[Should Not Happen<br/>Invalid OPTYP]
    E -->|Yes| G[Skip DSORT<br/>GO NEWOP Directly]
    G --> H[NEWOP: Check Function<br/>IF A=42 THEN]
    H --> I[Copy MEMAD and ABFUN<br/>X.MEMAD=MEMAD<br/>X.ABFUN=ABFUN]
    I --> J[Setup Parameters:<br/>0=ABP31<br/>100=ABP32]
    J --> K[Clear Inquiry Flag<br/>SCDFA.SUTYP BZERO 5SCIN]
    K --> L[Set B = SCDFA<br/>Device Datafield]
    L --> M[RETRY Loop Start]
    M --> N{SUTYP has 5SCIN?}
    N -->|No AND Not 3SNTR| O[Auto-Inquiry Required]
    N -->|Yes| P{SCOCW has 3SF42?}
    O --> Q{3SF42 Bit Set?}
    Q -->|Yes| R[Execute Function 42<br/>Set ABFUN=42]
    Q -->|No| S[Execute Function 36<br/>Standard Inquiry]
    R --> T[Inquiry Loop]
    S --> T
    T --> U[Call SCSID Driver<br/>T=X]
    U --> V{Result?}
    V -->|Sense 6 or 13| W[Unit Attention/Aborted<br/>Decrement TACOU]
    V -->|Success D<=1| X{Device Type Valid?}
    V -->|Other Error| Y[GO FAR ERREX]
    W --> T
    X -->|SUTYP SHZ -10><0| Z[TYPER Error<br/>Illegal Device Type]
    X -->|Valid| P
    P -->|Yes| AA[Setup READ Operation<br/>177700/\ABFUN Clear Function]
    P -->|No| AB[Regular Operation Path]
    AA --> AC[Get Control Record Address<br/>MEMA1, MEMA2, offset +10]
    AC --> AD[Setup Disk Address<br/>L.ABPA2 from Control Record]
    AD --> AE[Set Parameters:<br/>0=ABP31<br/>1=ABP32 Single Sector]
    AE --> AF[Calculate Buffer Address<br/>MEMAD + 1000]
    AF --> AG[Set T=X Parameter Pointer]
    AG --> AH[Call SCSID Driver<br/>377/\SCOCW control]
    AH --> AI{Read Success?}
    AI -->|Sense 6 or 13| AJ[Retry on Unit Attention]
    AI -->|Success| AK[GO FINEX<br/>Process Results]
    AI -->|Error| Y
    AJ --> M
    AK --> AL[Check 3SF42 Bit<br/>T=X.DQOPC BIT 3SF42]
    AL --> AM{Function 42 Result?}
    AM -->|Yes| AN[Check HSTAT<br/>A=X.HSTAT BZERO 17<=1]
    AM -->|No| AO[Regular Completion]
    AN --> AP[Clear Cache<br/>T=SCCLR, *EXR ST]
    AP --> AQ[Read First Word<br/>T=MEMA1, X=MEMA2<br/>*LDATX 00]
    AQ --> AR[Extract NPART<br/>A SHZ -10=NPART<br/>L=-1000=LOOPC]
    AR --> AS[Initialize Checksum<br/>D=0]
    AS --> AT[FOR LOOPC Loop<br/>XOR All Words]
    AT --> AU[Load Next Word<br/>*LDATX 00]
    AU --> AV[Calculate Checksum<br/>D XOR A]
    AV --> AW[Increment Address<br/>X+1]
    AW --> AX{More Words?}
    AX -->|Yes| AT
    AX -->|No| AY{Valid Checksum?<br/>D><0 OR L<=2 OR L>NCOPA}
    AY -->|Invalid| AZ[NOCRC Error<br/>No Control Record]
    AY -->|Valid| BA[Calculate Buffer Size<br/>NPART*6=L]
    BA --> BB[Get Source Address<br/>MEMAD + 2]
    BB --> BC[Copy Partition Table<br/>X=CMAD1, T=CMAD2<br/>*MOVPP L words]
    BC --> BD[Load Data Area Size<br/>T=CMAD1, X=CMAD2<br/>*LDDTX 40]
    BD --> BE[Return to User<br/>T=SLINK.MEMA1<br/>X=X.MEMA2<br/>*STDTX 10]
    BE --> BF[Store UHLIM<br/>AD=UHLIM<br/>36, *STATX 00]
    BF --> BG[Update SLINK.HSTAT<br/>Status Complete]
    BG --> BH[Set T=0<br/>Success Status]
    BH --> BI[RETEX: Cleanup<br/>B=D, X=ULINK]
    BI --> BJ[Clear STPRW<br/>0=STPRW]
    BJ --> BK[Call RETOP<br/>Terminate Operation]
    BK --> BL[Clear SLINK<br/>0=SLINK]
    BL --> BM[Decrement SUNOP<br/>SUNOP-1=SUNOP]
    BM --> BN[Return to Scheduler<br/>GO SWT11]
    AO --> BI
    AZ --> BI
    Z --> BI
    Y --> BI
    F --> BN

    style BN fill:#ccffcc
    style AZ fill:#ffcccc
    style Z fill:#ffcccc
    style Y fill:#ffcccc
    style F fill:#ffcccc

8.10 Error Code Mapping

graph TD
    A[RETOP Called<br/>T=Driver Status<br/>A=Sense Key] --> B{T == 0?<br/>Driver Success}
    B -->|No| C[Serious Error<br/>T SHZ 11 -> L<br/>L = 100020]
    B -->|Yes| D{Function 2 or 62?<br/>Compare Operation}
    C --> E[Set Status<br/>Bit 15 + Bit 4]
    D -->|Yes| F{Sense Key 5?<br/>Illegal Request}
    D -->|No| G[Map Sense Key<br/>via NEWST Array]
    F -->|Yes| H[Clear Sense<br/>L=0 Not Implemented]
    F -->|No| G
    H --> G
    G --> I[Bank 1 Access<br/>*1BANK]
    I --> J[Get NEWST Value<br/>X=17/\L<br/>NEWST X]
    J --> K[Update Status<br/>A\/X]
    K --> L[Bank 2 Access<br/>*2BANK]
    L --> M{HSTAT Bit 4?<br/>Error Flag Set}
    E --> M
    M -->|Yes| N[Set Error Bit<br/>L BONE 4]
    M -->|No| O{3SNTR Bit?<br/>Neutral Operation}
    N --> P[Update Status Words<br/>T=L=SCOSS=X.XSTAT]
    P --> Q[Save Function<br/>T=X.ABFUN=X.DMTRG]
    Q --> R{A<0 AND 3SERR?<br/>Log Error}
    R -->|Yes| S[Get Device Number<br/>A=B, CALL PHLOG<br/>A=9XDV]
    R -->|No| O
    S --> T[Extract Function<br/>SVXRG.ABFUN=9XFU]
    T --> U[Extract Unit<br/>A SHZ -6/\7=9XUN]
    U --> V[Copy Memory Address<br/>X.MEMAD=9XMA]
    V --> W[Copy Disk Parameters<br/>X.ABPA2=9XDA<br/>X.ABP32=9XTA]
    W --> X[Copy Status<br/>SCOSS=9XST]
    X --> Y[Get Program ID<br/>X=X.RTRES]
    Y --> Z[Bank 1 Access<br/>*1BANK]
    Z --> AA[Report Error<br/>CALL 9FLEX 9XER,12]
    AA --> AB[Bank 2 Access<br/>*2BANK]
    AB --> O
    O -->|Yes| AC[Return Original Status<br/>SCOSS=X.HSTAT]
    O -->|No| AD[Use Computed Status]
    AC --> AE[Disable Interrupts<br/>*IOF]
    AD --> AE
    AE --> AF[Return to Level 11<br/>CALL TO11Q]
    AF --> AG[Enable Interrupts<br/>*ION]
    AG --> AH[Restore Registers<br/>SVTAD, SVXRG]
    AH --> AI[Return via SVLRG<br/>GO SVLRG]

    subgraph "NEWST Mapping (Sense Key -> Status)"
        BA[Sense 0: No Sense<br/>040000]
        BB[Sense 1: Recovered Error<br/>040000]
        BC[Sense 2: Not Ready<br/>100020]
        BD[Sense 3: Medium Error<br/>140020]
        BE[Sense 4: Hardware Error<br/>140220]
        BF[Sense 5: Illegal Request<br/>140020]
        BG[Sense 6: Unit Attention<br/>140020]
        BH[Sense 7: Data Protect<br/>040020]
        BI[Sense 8: Blank Check<br/>040020]
        BJ[Sense 9: Vendor Specific<br/>140020]
        BK[Sense 10: Copy Aborted<br/>150020]
        BL[Sense 11: Aborted Command<br/>140020]
        BM[Sense 12: Equal<br/>040000]
        BN[Sense 13: Volume Overflow<br/>140020]
        BO[Sense 14: Miscompare<br/>042020]
        BP[Sense 15: Reserved<br/>140020]
    end

    subgraph "SCDTS Mapping (Driver -> SINTRAN)"
        CA[TYPER -> 240<br/>Illegal Device Type]
        CB[ILAOP -> 201<br/>Illegal Function]
        CC[BADPA -> 174<br/>Illegal Parameter]
        CD[ILNOD/NOLUN -> 33<br/>No Such LUN]
        CE[COPNP -> 3206<br/>Illegal Request]
        CF[TRANE -> 141<br/>Transfer Error]
        CG[SBUSY -> 3207<br/>Device Busy]
        CH[RCONF -> 3210<br/>Reservation Conflict]
        CI[NESER -> 3211<br/>Device No Answer]
        CJ[Other -> 232<br/>Device Error]
    end

    style AI fill:#ccffcc
    style AA fill:#ffccaa

Cross-Reference

This document describes the high-level disk/tape subsystem. For low-level SCSI protocol and hardware interface details, see:

Source Code\Sintran L\NPL\IP-P2-SCSI-DRIV-ANALYSIS.md

Key cross-references: - SCSID entry point (lines 1102-1549): Low-level SCSI command execution - SCLLD entry point (lines 93-117): NCR controller interface - Hardware registers and interrupt handling: Detailed in SCSI-DRIV-ANALYSIS.md - Phase handlers (Data, Command, Status, Message): Described in driver analysis - Error recovery sequences: Documented in driver interrupt flow

Summary

The IP-P2-SCSI-DISK module provides three integrated subsystems:

  1. CTRSCSI: Generic SCSI controller interface for all device types
  2. SCSDISK: Advanced disk driver with elevator algorithm and partition management
  3. SCSTREAM: Tape streamer driver with variable/fixed block modes

Key Features: - 64 function codes covering disk, tape, and generic SCSI operations - Elevator (SCAN) algorithm for optimal disk head scheduling - Partition access control with read/write validation - Comprehensive error handling with retry logic and detailed logging - Auto-inquiry for dynamic device detection - Copy operations between tape and disk on same SCSI bus

Performance Optimizations: - Queue sorting by disk address (elevator algorithm) - Direction reversal at queue boundaries - Parallel seek on multi-unit configurations - Retry with exponential backoff for transient errors

The driver integrates tightly with the SINTRAN operating system, supporting multi-programming environments with proper queue management and interrupt handling.

Document Version: 1.0 Last Updated: 2025-10-13 File Path: Source Code\Sintran L\NPL\IP-P2-SCSI-DISK.md