1 files changed, 223 insertions, 0 deletions

diff --git a/v4.0/src/DEV/SMARTDRV/EMM.ASM b/v4.0/src/DEV/SMARTDRV/EMM.ASM
new file mode 100644
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--- /dev/null
+++ b/v4.0/src/DEV/SMARTDRV/EMM.ASM
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+BREAK   <EMM control sector layout>
+
+;
+; The EMM control sector is a 1024 byte record which ALWAYS occupies the
+; very first 1024 bytes of "extra" memory that needs to be managed. Its
+; function is to provide a method to allocate available "extra" memory
+; to programs which desire to use it and avoid program conflicts that
+; would occur if two different programs attempted to use the same piece
+; of "extra" memory.
+;
+
+;
+; The EMM_CTRL structure defines the offsets into the 1024 byte control
+; sector of the various fields. The EMM_REC structure defines a sub-structure
+; contained within the EMM_CTRL structure which represents a particular
+; piece of allocated "extra" memory (an allocation record).
+;
+
+; Layout of each EMM record.
+
+EMM_REC         STRUC
+EMM_FLAGS       DW      0
+EMM_SYSTEM      DW      0
+EMM_BASE        DD      ?               ; 24 bit address of start of region
+EMM_KSIZE       DW      ?               ; Size of region in kbytes
+EMM_REC         ENDS
+
+; EMM_FLAGS Bits
+EMM_ALLOC       EQU     0000000000000001B       ; Zero -> record is free
+EMM_ISDRIVER    EQU     0000000000000010B       ; 1 -> driver is installed
+                                                ;      for this region
+
+; EMM_SYSTEM Values
+EMM_EMM         EQU     0                       ; Allocated to EMM
+EMM_MSDOS       EQU     1
+EMM_XENIX       EQU     2
+EMM_APPLICATION EQU     3
+
+; Layout of EMM control 1024 byte record
+
+EMM_CTRL        STRUC
+EMM_VER         DB      50 DUP(?)
+EMM_TOTALK      DW      ?               ; EXCLUDING the 1k of this record
+EMM_AVAILK      DW      ?               ; Amount of above NOT allocated
+                DB      SIZE EMM_REC DUP(?) ; NULL (0th) RECORD
+EMM_RECORD      DB      (1024 - 50 - 4 - 10 - (SIZE EMM_REC)) DUP(?)
+                                          ; EMM_REC structures
+EMM_TAIL_SIG    DB      10 DUP(?)
+EMM_CTRL        ENDS
+
+EMM_NUMREC      EQU     (1024 - 50 - 4 - 10 - (SIZE EMM_REC)) / (SIZE EMM_REC)
+
+
+;
+; The current initial (no "extra" memory allocated) EMM_CTRL sector is
+;
+;  EMM_CONTROL   LABEL   BYTE
+;                  DB      "MICROSOFT EMM CTRL VERSION 1.00 CONTROL BLOCK     "
+;                  DW      EXTMEM_TOTALK - 1
+;                  DW      EXTMEM_TOTALK - 1
+;          ; NULL 0th record
+;                  DW      EMM_ALLOC + EMM_ISDRIVER
+;                  DW      EMM_EMM
+;                  DW      EXTMEM_LOW + 1024
+;                  DW      EXTMEM_HIGH
+;                  DW      0
+;          ;**
+;                  DB      950 DUP(0)
+;                  DB      "ARRARRARRA"
+;
+; Where EXTMEM_LOW:EXTMEM_HIGH is the 32 bit address of the first byte
+; of the EMM_CTRL sector (first byte of "extra" memory) and EXTMEM_TOTALK
+; is the size in K of the available "extra" memory. One is subtracted
+; from EXTMEM_TOTALK because the sizes in the EMM_CTRL record DO NOT
+; include the 1k taken up by the EMM_CTRL sector.
+;
+; The reason for the existance of the NULL 0th record is to facilitate
+; the computation of EMM_BASE for the first EMM_REC allocation record
+; created.
+;
+; The EMM_REC structures CANNOT be sparse. In other words if one sets
+; up a scan of the EMM_REC structures in the EMM_CTRL sector, as soon as
+; an EMM_REC structure WITHOUT the EMM_ALLOC bit set in its flag word
+; is encountered it is not necessary to scan further because it IS KNOWN
+; that all of the EMM_REC structures after the first one with EMM_ALLOC
+; clear also have EMM_ALLOC clear. What this means is that EMM_CTRL
+; memory CANNOT BE deallocated. Once an EMM_REC structure has its
+; EMM_ALLOC bit set, there is NO correct program operation which
+; can clear the bit UNLESS it IS KNOWN that the next EMM_REC structure
+; has its EMM_ALLOC bit clear or the EMM_REC structure is the last one.
+;
+;
+; USING THE EMM_CTRL SECTOR:
+;
+;    A program which wishes to use the EMM_CTRL sector to access "extra"
+;    memory should work as follows:
+;
+;       Figure out how much memory you wish to allocate
+;
+;       Figure out the location and size of the "extra" memory in the system
+;
+;       IF (the first 1024 bytes of "extra" memory DO NOT contain a valid
+;        EMM_CTRL record determined by checking for the existence of the
+;        correct EMM_VER and EMM_TAIL_SIG strings)
+;               Write a correct initial EMM_CTRL sector to the first 1024
+;                bytes of extra memory. Be sure to fill in EMM_TOTALK,
+;                EMM_AVAILK and EMM_BASE in the 0th record.
+;
+;       Set up a scan of the EMM_REC structures in the EMM_CTRL sector.
+;        NOTE: You can skip the NULL 0th record if you want since it has
+;              known value.
+;
+;       FOR (i=0;i<EMM_NUMREC;i++)
+;               IF ( this EMM_REC has EMM_ALLOC clear)
+;                       IF ( EMM_AVAILK < amount I want to alloc)
+;                               ERROR insufficient memory
+;                       EMM_AVAILK = EMM_AVAILK - amount I want to alloc
+;                       EMM_FLAGS = EMM_ALLOC + EMM_ISDRIVER
+;                       EMM_KSIZE = amount I want to alloc
+;                       EMM_SYSTEM = appropriate value
+;                       EMM_BASE = EMM_BASE of PREVIOUS EMM_REC +
+;                                    (1024 * EMM_KSIZE of PREVIOUS EMM_REC)
+;                       break
+;               ELSE
+;                       address next EMM_REC structure
+;
+;       IF (i >= EMM_NUMREC)
+;               ERROR no free EMM_REC structures
+;
+;
+; You can now see why we need that NUL 0th EMM_REC structure. In order to
+; perform this step
+;
+;       EMM_BASE = EMM_BASE of PREVIOUS EMM_REC +
+;                    (1024 * EMM_KSIZE of PREVIOUS EMM_REC)
+;
+; when the very first EMM_REC is allocated we must have a "previous EMM_REC"
+; structure to point at.
+;
+; The above code is rather simplistic in that all it does is do a simple
+; allocation. The EMM_ISDRIVER bit allows us to do some more sophisticated
+; things. In particular in the case of a RAMDrive type of program it is
+; desirable to "re-find" the same RAMDrive area in "extra" memory when the
+; system is re-booted. The EMM_ISDRIVER bit is used to help us do this.
+;
+; The EMM_ISDRIVER bit means "there is presently a piece of code in the
+; system which is using this memory". If we find an EMM_REC structure
+; which has its EMM_ALLOC bit set, but the EMM_ISDRIVER bit is clear
+; it means that the piece of code that originally allocated
+; the memory is gone and we may want to "re-find" this memory by
+; setting the EMM_ISDRIVER bit again. A RAMDrive program would have
+; slightly different code than the above:
+;
+;       FOR (i=0;i<EMM_NUMREC;i++)
+;               IF ( this EMM_REC has EMM_ALLOC clear)
+;                       IF ( EMM_AVAILK < amount I want to alloc)
+;                               ERROR insufficient memory
+;                       EMM_AVAILK = EMM_AVAILK - amount I want to alloc
+;                       EMM_FLAGS = EMM_ALLOC + EMM_ISDRIVER
+;                       EMM_KSIZE = amount I want to alloc
+;                       EMM_SYSTEM = appropriate value
+;                       EMM_BASE = EMM_BASE of PREVIOUS EMM_REC +
+;                                    (1024 * EMM_KSIZE of PREVIOUS EMM_REC)
+;                       break
+;               ELSE
+;                       IF ((EMM_SYSTEM == my value for EMM_SYSTEM) &&
+;                           (EMM_ISDRIVER is clear))
+;                               deal with differences between amount
+;                                I want to allocate and EMM_KSIZE
+;                               Set EMM_ISDRIVER
+;                               EMM_BASE is the base address of this piece
+;                                of memory and EMM_KSIZE is its size.
+;                               break
+;                       address next EMM_REC structure
+;
+; In this way we "re-find" memory that was previosly allocated (presumably
+; by us, or a related program).
+;
+; NOTE THAT THIS USE OF EMM_ISDRIVER REQUIRES SOME MECHANISM FOR CLEARING
+; EMM_ISDRIVER WHEN THE CODE OF INTEREST IS REMOVED FROM THE SYSTEM.
+; In the case of a RAMDrive program the code is removed whenever the system
+; is re-booted. For this reason a RAMDrive program will need code that is
+; invoked whenever a system re-boot is detected. What this code does is
+; scan the EMM_REC structures in the EMM_CTRL sector turning off the
+; EMM_ISDRIVER bits:
+;
+;       FOR (i=0;i<EMM_NUMREC;i++)
+;               IF ( this EMM_REC has EMM_ALLOC clear)
+;                       break
+;               ELSE IF (EMM_SYSTEM == my value for EMM_SYSTEM)
+;                       clear EMM_ISDRIVER bit
+;               address next EMM_REC
+;
+; Note that this code clears ALL of the ISDRIVER bits for EMM_SYSTEM
+; values of a certain value. This means there is a GLOBAL piece of
+; re-boot code for ALL of the programs using a particular EMM_SYSTEM
+; value. An alternative is to have each EMM_CTRL user clear the
+; EMM_ISDRIVER bits ONLY for those EMM_REC structures that it allocated.
+; This requires that the program keep a record of which EMM_REC structures
+; it is responsible for:
+;
+;       FOR each of my EMM_REC structures
+;               INDEX this EMM_REC structure in the EMM_CTRL sector
+;               Clear EMM_ISDRIVER
+;
+; NOTE about this step:
+;
+;       deal with differences between amount
+;        I want to allocate and EMM_KSIZE
+;
+; in the above code. There are a lot of options here depending on the desired
+; behavior. If the NEXT EMM_REC structure has EMM_ALLOC clear, then it may
+; be possible for me to grow or shrink the block I found by adjusting
+; EMM_KSIZE and EMM_AVAILK. If the NEXT EMM_REC structure has EMM_ALLOC
+; set, then I am forced to either adjust the amount I want to allocate
+; to match EMM_KSIZE, or skip this EMM_REC without setting EMM_ISDRIVER.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+; for rom 1nt15 extended memory interface
+emm_int      equ    15h
+emm_size     equ    88h
+emm_blkm     equ    87h
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;