add directory study

study/sabre/os/files/Executables/SYS.txt

@@ -0,0 +1,86 @@
+===========================================================================
+From: BRIAN FRASER                 Refer#: NONE
+  To: MATHIEU BOUCHARD              Recvd: NO  
+Subj: .SYS format.                   Conf: (99) 80xxxProgr
+---------------------------------------------------------------------------
+
+Main Header:
+
+00h word  - Link to next driver, offset
+02h word  - Link to next driver, segment
+04h word  - Device Attribute
+06h word  - Strategy entry point, offset
+0ah word  - interrupt entry point, offset
+-- Character device --
+0ch 8 bytes - Logical Name
+-- Block device --
+0ch byte  - Number of units
+
+
+Header Attribute word:
+bit 15    - 1= Character device; 0= Block device
+bit 14    - 1= IOCTL read and write supported
+-- Character device --
+bit 13    - 1= Output until busy supported
+-- Block device --
+bit 13    - 1= Check BIOS to determine media characteristics; 0= Media ID
+               should be used instead
+bit 12    - should be 0
+bit 11    - 1= if open/close/removable media supported
+bit 7-10  - 0
+bit 6     - 1= if generic IOCTL and get/set logical drive supported
+bit 5     - 0
+bit 4     - 1= if CON driver and int 29h fast-output supported
+bit 3     - 1= if current CLOCK$ device
+bit 2     - 1= if current NULL device
+-- Character device --
+bit 1     - 1= if standard output device (stdout)
+-- Block device --
+bit 1     - 1= if 32bit sector addressing supported
+bit 0     - 1= if current standard input device (stdin)
+
+
+Strategy Request Header:
+00h byte  - length of request header
+01h byte  - unit number for this request
+02h byte  - request headers command code
+03h word  - drivers return status
+05h 8 bytes - ? (reserved)
+
+The rest of the header varies depending on what function is being called.
+
+I would think it's best to find a book, as I don't really want to type out all
+the different headers for each function. :)
+
+This book I am using is Advanced MS-DOS, Second Ed. Provided, it's a little out
+of date, but alot of the information is still the same. Plus, I got it for 8
+bucks.. Can't complain for that price! :)  Check out the book list.
+
+
+Heres just a little info on what the above headers are for...
+
+There are two different kinds of device drivers. Character, and Block.
+Character devices handle 1 character at a time, while Block devices deal with
+Blocks of data. Character devices can have a logical name like "MYSYS", which
+can be used like "CON" or "PRN" etc.. Block devices use units (drives), which
+are assigned upon install.
+
+The Main Header is the first few bytes of the SYS file, The link to next driver
+is to be -1:-1 (or FFFF:FFFF) unless there is more then one driver in this SYS
+file, then you set this to the next driver in the chain. BUT, the last driver
+must have FFFF:FFFF as the next driver, or you have big problems! :)
+
+The Device attribute is fairly strate forward.
+
+The strategy routine is a routine that is called my DOS with the address of the
+Request Header. All this routine has to do is save the address in a local
+memory location.
+
+The interrupt routine is then called after the strategy routine. The interrupt
+routine process the request header, and performs the requested function, and
+returns.
+
+If you can't find a book.. Maybe I'll type out the return attributes, and the
+info for each function.
+
+       Brian