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MON 333B (octal) - DMAFunction (UDMA)

Various DMA (Direct Memory Access) functions on a DMA-channel device: receive/send DMA data (with/without wait), read/clear DMA status, read last status, and use programmed I/O devices. This is an ND-100 monitor call (also available on ND-500).

Status: partial. GOTAB[333B] = 112561B (byte-proven) routes to the DIA11 DMA-device entry stub in overlay 025-S3IRPIT - real code that saves the caller register block and switches page context (TRR PCR). The worker UDMA = 110770B (same overlay) is real code: a function-code decoder that matches FuncCode against the manual's DMA function codes (0,1,2,3,7,20,21,24,54..57) and builds a device control word. The DIA11 -> UDMA link crosses the TRR PCR context switch / resident CALLPROC bridge (uncarved), so it is attributed by symbol + the matching function codes, not a followed pointer (see Honest caveats). All addresses/values are octal.

Dispatch path

flowchart LR
    A["User/RT program<br/>MON 333B"] --> B["ENT14 level-14<br/>T = device no"]
    B --> C["GOTAB[333B] = 112561B<br/>(byte-proven)"]
    C --> D["DIA11 entry stub<br/>025-S3IRPIT :112561B"]
    D -.uncarved TRR PCR / CALLPROC.-> E["UDMA worker<br/>025-S3IRPIT :110770B"]
    E --> F["FuncCode decode<br/>build DMA control word"]
    class A blue
    class B,C,D teal
    class E teal
    class F green
    classDef blue fill:#E3F2FD,stroke:#0D47A1,color:#0D47A1
    classDef teal fill:#E0F7FA,stroke:#00838F,color:#00838F
    classDef green fill:#E8F5E9,stroke:#2E7D32,color:#2E7D32

The dashed hop (D ⇢ E) is the page-context switch (TRR PCR) plus the resident CALLPROC second-level dispatch - not present in any carved segment, so the exact DIA11 -> UDMA transfer cannot be followed statically. Both endpoints are real bytes in 025-S3IRPIT.

Code location (dispatch path)

Every row is a real region you can open. Byte offset = (addr − loadbase) in octal words × 2 (decimal); commoncode load base is 0, 025-S3IRPIT load base is 32000B.

Role Segment (full disasm) Addr range (octal) Byte offset Symbol Verdict
GOTAB[333] dispatch word commoncode.asm · .hex 071566B (1 word) 59116 GOTAB+333 = 112561B VERIFIED
DIA11 entry stub 025-S3IRPIT.asm · .hex 112561B-112615B (29 words) 49890 DIA11 VERIFIED (real stub)
context switch / CALLPROC bridge — (uncarved) — — TRR PCR / CALLPROC UNVERIFIED
UDMA worker body 025-S3IRPIT.asm · .hex 110770B-111120B (code) 48112 UDMA real bytes; link inferred

Verify by hand (GOTAB word): grep '^71566 ' ../../segments-ref/SINTRAN-DATA_commoncode/SINTRAN-DATA_commoncode.hex → 71566 112561 225 161 59116; then dd if=../../../resident/SINTRAN-DATA_commoncode.bin bs=1 skip=59116 count=2 2>/dev/null | od -An -tx1 → 95 71 (= octal 112561, the DIA11 dispatch address).

Verify by hand (DIA11 stub): grep '^112561 ' ../../segments-ref/025-S3IRPIT/025-S3IRPIT.hex → byte offset 49890, value 150401; then dd if=../../../segments/025-S3IRPIT.bin bs=1 skip=49890 count=2 2>/dev/null | od -An -tx1 → d1 01 (= octal 150401, IOF, the stub's first word).

Verify by hand (UDMA worker): grep '^110770 ' ../../segments-ref/025-S3IRPIT/025-S3IRPIT.hex → byte offset 48112, value 135131; then dd if=../../../segments/025-S3IRPIT.bin bs=1 skip=48112 count=2 2>/dev/null | od -An -tx1 → ba 59 (= octal 135131, JPL I 131, the worker's first word). prove-mon.py 333 reports the same GOTAB[333]=112561 -> DIA11.

Instruction walkthrough

Full listing: 333B-DMAFunction.ASM. All addresses octal; X = saved register block, B = per-call DMA datafield (roles inferred from the access pattern).

DIA11 entry stub (112561-112615) — the level-14 DMA entry. It goes IOF / TRR PCR (page context switch) / stages the caller A into a register block (LDX I 76 -> [112661B] ; STA ,X 17) / ION, then stages the parameter word (,B 20) and the MON number (STT ,X 0) with a second TRR PCR, and JMPs into the shared disk/DMA-stub tail. VERIFIED (bytes).

UDMA function decoder (110770-111120) — after setup (JPL I 131/130) and a non-zero check (SKP IF DA UEQ 0), it enables interrupt bits (SAA 4 ; MST PIE) and stages a DMA descriptor with the register-block moves LRB 4 / SRB 40. It then clears the control word (SAA 0 ; RADD CLD SA DD → D = 0) and 111020 LDA ,B 20 fetches FuncCode. A ladder of SAT n / SKP IF DA EQL ST comparisons matches the manual's codes and sets the corresponding BSET ONE bit in D (bit number = the nd100-dis printed field >>3: func 0 → bits 0+2; func 1 → bit 1; func 2/3 → bit 3; func 20/24 → bits 2+4; func 54/56 → bit 5; func 55/57 → bit 6; func 7/62 → bit 2; func 21/64/65/70 → indirect worker via JMP I 10 -> [111130]). VERIFIED (bytes); the meaning of each control bit is inferred.

Shared status-store tail (111131-111132) — RADD CLD SD DA copies the built control word from D into A, and STA ,B 35 stores it to the caller datafield. Words 111121-111130 are the JPL-I pointer/data table (they disassemble as bogus instructions); their callees are outside this carve.

Parameter / register contract

Manual-side names/types are from 333B_DMAFunction.yaml.

Reg / field Dir Meaning Verdict
DeviceNo (T) in logical device number of a DMA channel inferred (manual LDT LDN)
FuncCode / ,B 20 in DMA function code (0..3,7,20,21,24,54..57) VERIFIED literals (111021-111116); meaning inferred
DataAddress io memory address of data (func 0:3) or PIO device no (func 54:57) inferred (manual)
InPara / OutPara io 32-bit function-dependent input/output parameters inferred (manual)
control word (reg D) work device control word built bit-by-bit per FuncCode, stored to ,B 35 VERIFIED (111016-111132)
ErrCode out standard error code (appendix A) inferred (manual)

The concrete DMA operation each control bit triggers, and the indirect workers reached through [111130], need live device context and are outside the carved window.

Pseudo-code (for an emulator)

See 333B-DMAFunction.pseudo.c — a pseudo-C model for emulator authors. The DIA11 register-block save + TRR PCR context switch and the UDMA FuncCode decoder (the SAT/SKP IF DA EQL ST comparisons and the BSET ONE control-word bits) are byte-verified; the meaning of each control bit and the caller-side parameter list are inferred from the manual.

Every instruction in the .pseudo.c is translated against the canonical ND100-INSTRUCTION-SEMANTICS.md (RADD CLD SA DD = D = A COPY; SKP IF DA EQL ST = if (A == T) skip; SKP IF DA UEQ ST = if (A != T) skip; BSET ONE b Dr = reg |= (1<<b) with bit number = printed field >>3; SAT n = T := n; MST PIE = masked-set of the interrupt-enable register; LRB/SRB = load/store 8-word register block via the alt page table).

Honest caveats

What is byte-proven: GOTAB[333B] = 112561B routes to DIA11 (real code, first word 150401 = IOF); the DIA11 stub's IOF/TRR PCR/ION critical section and register-block staging; the UDMA worker at 110770B (first word 135131 = JPL I 131); the FuncCode ladder whose literal codes (0,1,2,3,7,20,21,24,54,55,56,57,...) match the manual's DMA function codes; the BSET ONE control-word construction in register D; the store to ,B 35.

What is NOT proven: the DIA11 -> UDMA link and the physical DMA operation each control bit drives. DIA11 switches page context with TRR PCR and re-enters through the resident CALLPROC bridge in an uncarved overlay; the device-side workers reached through [111130] sit past the carve. Attributing the body to UDMA rests on the symbol name (UDMA = User DMA) plus the FuncCode match with the manual, not a followed pointer.

This reconciles into one story: the dispatch head (GOTAB[333] -> DIA11) is solid; the DIA11 stub and the UDMA decoder are both real bytes in 025-S3IRPIT; the transfer between them and the leaf DMA workers cross the uncarved context-switch/pointer layer. Confirming the exact link needs a live trace (break at 112561B on a real MON 333, single-step the TRR PCR switch, and record where P lands).

Method: ../../../../../EXTRACTING-RESIDENT-CODE.md · dispatch reality: ../../TASK-05-mismatches.md · master map: ../../MON-CALL-INDEX.md.