[HECnet] Re: Sector interleave for RX01/2

Thanks for all the answers, and thanks to Johnny for providing a pointer to the DX driver code. FWIW, the DX driver performs the logical to physical translation using a "logical sector number", where each logical block contains four consecutive logical sectors. The routine that converts an LSN to a track and sector, and handles interleave and skew at the same time, is below. I'm not even going to pretend I know how this works - it's a bit obscure - but it's straight forward enough to translate it literally into C. Bob ;+ ; *** - TRKSEC - CONVERT LOGICAL OR PHYSICAL BLOCK NUMBER TO ; TRACK-SECTOR PAIR ; FROM ALGORITHM BY J GILBERT MODIFIED BY H. JACOBS ; ; INPUT: ; R3 - I/O PACKET ADDRESS ; I.PRM+10(R3) - LOGICAL OR PHYSICAL SECTOR ; ; OUTPUT: ; I.PRM+14(R3) - SECTOR (1-26.) ; I.PRM+15(R3) - TRACK (0-77.) ; R3 - UNCHANGED ; C CLEAR - VALID BLOCK ; C SET - BAD BLOCK NUMBER (PHYSICAL OR LOGICAL) ; ;- TRKSEC: MOV I.PRM+10(R3),R1 ; GET LOGICAL OR PHYSICAL BLOCK MOV #8.,R0 ; SET LOOP COUNT MOV #6400,R2 ; SET DIVISOR 1$: CMP R2,R1 ; DOES 26 GO INTO DIVIDEND? BHI 2$ ; BRANCH IF NOT, C CLEAR SUB R2,R1 ; SUBTRACT 26 FROM DIVIDEND SEC ; SET CARRY 2$: ROL R1 ; SHIFT DIVIDEND AND QUOTIENT DEC R0 ; DONE? BGT 1$ ; NO, LOOP MOVB R1,R0 ; GET TRACK NUMBER CLRB R1 ; CLEAR TRACK NUMBER SWAB R1 ; SHIFT DONE SECTOR NUMBER BITB #IO.RPB&377,I.FCN(R3) ; PHYSICAL BLOCK WANTED? BNE 10$ ; YES CMP #12.,R1 ; NO, C=1 IF 13<=R1<=25 ROL R1 ; DOUBLE FOR INTERLEAVE FACTOR ASL R0 ; ADD TRACK -TRACK SKEW ADD R0,R1 ; SKEW BY 2*TRACK ADD R0,R1 ; SKEW BY 4*TRACK ADD R0,R1 ; SKEW BY 6*TRACK ASR R0 ; RESTORE TRACK NUMBER MOV #26.,R2 ; SET MODULUS 5$: SUB R2,R1 ; MODULO SECTOR INTO RANGE -26. TO -1. BGE 5$ ; LOOP TILL REMAINDER GOES NEG ADD R2,R1 ; CONVERT TO RANGE 0-25. INC R0 ; LBN0 STARTS ON TRACK 1 10$: INC R1 ; CONVERT TO RANGE 1-26. MOV R1,I.PRM+14(R3) ; SAVE SECTOR NUMBER MOVB R0,I.PRM+15(R3) ; SAVE TRACK NUMBER CMP #77.*256.,I.PRM+14(R3) ; IS IT A VALID TRACK/SECTOR? RETURN