=================== C-CODE CUT FROM NOVA_DKP.C ===============================



EACH NOVA I/O COMMAND SUPPLIES A REGISTER (AC0/AC1/AC2/AC3) WITH BITS TO TELL THE CONTROLLER WHAT TO DO



DOA SELECTS THE DRIVE, TRACK(SURFACE), AND SECTOR, AND SUPPLIES A NEGATIVE SECTOR COUNT

DOB PROVIDES THE MEMORY ADDRESS

DOC SELECTS THE CYLINDER AND SETS THE COMMAND (READ,WRITE,SEEK,RECAL)

	DOC ALSO CAN CLEAR DONE FLAGS IN THE CONTROLLER



DIA GETS CONTROLLER STATUS

DIB AND DIC RETRIEVE VALUES, BUT THESE ARE NOT USED IN IRIS



THE FOLLOWING SECTIONS EXPLAIN HOW THE BITS PROVIDED IN THE REGISTERS ARE INTERPRETED

BY A STANDARD DG CONTROLLER (AND BY SIMH)



NOTE THAT THERE ARE 2 MAJOR FORMATS, DUBBED 'OLD' AND 'NEW' IN THE CODE



/* ============== THIS IS SUPPLIED BY THE DOC COMMAND ================== */

/* Unit, surface, sector, count register



/*

    Original format: 2b, 6b, 4b, 4b

    5432109876543210 <<<<< BIT# */

    UUTTTTTTSSSSXXXX

 

    Revised format:  2b, 5b, 5b, 4b

    5432109876543210 <<<<< BIT# */

    UUTTTTTSSSSSXXXX



WHERE U = UNIT BITS / T = TRACK BITS / S = SECTOR BITS / X = COUNT BITS



*/



#define USSC_V_COUNT    0         (displacement)                      /* count */

#define USSC_M_COUNT    017  /* 4 BITS */



#define USSC_V_OSECTOR  4         (displacement)                      /* old: sector */

#define USSC_M_OSECTOR  017  /* 4 BITS */



#define USSC_V_OSURFACE 8         (displacement)                      /* old: surface */

#define USSC_M_OSURFACE 077  /* 6 BITS */



#define USSC_V_NSECTOR  4         (displacement)                      /* new: sector */

#define USSC_M_NSECTOR  037  /* 5 BITS */



#define USSC_V_NSURFACE 9         (displacement)                      /* new: surface */

#define USSC_M_NSURFACE 037  /* 5 BITS */



#define USSC_V_UNIT     14        (displacement)                      /* unit */

#define USSC_M_UNIT     03     /* 2 bits */







=============================================================================*/



/* ============== THIS IS SUPPLIED BY THE DOA COMMANDS ================== */

/* Flags, command, cylinder register



   Original format: 5b, 2b, 1b + 8b (surrounding command)

   

    5432109876543210 <<<<< BIT# */

    RDDDDMM0CCCCCCCC

 

   Revised format:  5b, 2b, 9b

    5432109876543210 <<<<< BIT# */

    RDDDDMMCCCCCCCCC



RDDDD = DONE FLAGS (R=READ/WRITE;  D=DRIVE SEEK, EACH BIT IS A DRIVE)

MM = MODE (READ, WRITE, SEEK, RECAL)





#define FCCY_V_OCYL     0                               /* old: cylinder */

#define FCCY_M_OCYL     0377

#define FCCY_V_OCMD     8                               /* old: command */

#define FCCY_M_OCMD     3

#define FCCY_V_OCEX     10                              /* old: cyl extend */

#define FCCY_OCEX       (1 << FCCY_V_OCEX)

#define FCCY_V_NCYL     0                               /* new: cylinder */

#define FCCY_M_NCYL     0777

#define FCCY_V_NCMD     9                               /* new: command */

#define FCCY_M_NCMD     3

#define  FCCY_READ      0

#define  FCCY_WRITE     1

#define  FCCY_SEEK      2

#define  FCCY_RECAL     3

#define FCCY_FLAGS      0174000                         /* flags */





=============================================================================*/



#define GET_SA(cy,sf,sc,t) (((((cy)*drv_tab[t].surf)+(sf))* \

    drv_tab[t].sect)+(sc))



=============================================================================*/



notice that the simh supported drives fall into 2 categories based on

whether they use the old or new format



The logic for all of them is similar, but the bit placement varies by format

and the max# allowed in each area is limited by the drive characteristics









/* This controller supports many different disk drive types:



   type         #sectors/       #surfaces/      #cylinders/     new format?

                 surface         cylinder        drive



   floppy       8               1               77              no

   Diablo 31    12              2               203             no

   Century 111  6               10              203             no

   4048 (same as Century 111)

   Diablo 44    12              4               408             no

   Century 114  12              20              203             no

   4057 (same as Century 114)



   DS/DD floppy 16              2               77              yes

   (6097 "quad floppy")

   6225         20              2               245             yes

   6099         32              4               192             yes

   6227         20              6               245             yes

   6070         24              4               408             yes     

   6103         32              8               192             yes

   4231         23              19              411             yes