Writing MS-DOS Device Drivers
By Marcus Johnson, December 01, 1990
December 1990/Writing MS-DOS Device Drivers/Listing 8
/* This is used for the escape buffer. This is how many
* bytes of parameters the escape() routine can save in one
* sequence. Tune it as you see fit. It needs to be at
* least long enough to hold the two bytes of an extended
* key (such as F1), plus the replacement string: */
#define BUF_LEN 80
/* length of the definition field; tune as you see fit.
* How long a string do you want? */
#define KEY_BUFLEN 21
/* number of re-assignments you can define;
* tune as you see fit. Don't use it much?
* make it less. Redefining the entire keyboard?
* then make it more */
#define NKEYS 20
/*
* parameters for the ring buffer. If you want to
* change the size, just change RLOG - the math demands
* that the size of the buffer be a power of 2. Makes
* things nice and efficient that way.
*/
#define RLOG 6
#define RLEN (2 << (RLOG - 1))
#define RLIMIT (RLEN - 1)
/*
* macros for reading the system RAM where these neat
* things are stored
*/
#define CURRENT_MODE (*(char far *)0x0449)
#define SCREEN_WIDTH (*(char far *)0x044A)
#define SCREEN_OFFSET (*(unsigned far *)0x044E)
#define PAGE_TABLE ((POSITION far *)0x0450)
#define CURRENT_PAGE (*(char far *)0x0462)
/*
* base addresses for the video memory for the
* monochrome adaptor (MONOCHROME) and the CGA (GRAPHIC)
*/
#define MONOCHROME ((char far *) 0x000B0000)
#define GRAPHIC ((char far *) 0x000B8000)
/*
* status bits for the return code
*/
#define UNKNOWN_COMMAND 03
#define ERROR 0x8000
#define DONE 0x0100
#define BUSY 0x0200
/*
* the states of the escape sequence:
*
* RAW: no escape sequence begun yet, or previous
* sequence has been terminated
*
* HAVE_ESC: an escape has been received; now awaiting
* the left bracket
*
* HAVE_LBRACE: an escape followed by a left bracket
* have been received; now waiting for a
* parameter or terminating character
*
* IN_STRING: a parameter beginning with a delimiter has
* been started; until the same delimiter is
* received, characters will be placed in the
* escape buffer as is
*
* IN_NUMBER: a numeric parameter has been started; each
* subsequent digit is 'added' to the number
* in the escape buffer
*/
#define RAW 0
#define HAVE_ESC 1
#define HAVE_LBRACE 2
#define IN_STRING 3
#define IN_NUMBER 4
/* typedef for cursor positioning; this union reflects the way
* that they are stored internally. At the assembly language
* level, 16-bit registers can be loaded directly with the
* 16-bit position so that the high and low halves are
* correctly loaded for BIOS calls
*/
typedef union
{
short position;
struct
{
char col;
char line;
} loc;
} POSITION;
/*
* typedef for the reassignment buffer. keystroke is the key
* being replaced; length is the number of bytes that the
* keystroke 'generates'; buffer holds the data that replaces
* the keystroke.
*/
typedef struct
{
int keystroke;
char length;
char buffer [ KEY_BUFLEN ];
} KEY;
/*----------- global variables -----------*/
/* the current character being output */
extern char outchar;
/* the current video mode */
extern char video_mode;
/* the current screen attribute */
extern char attrib;
/* a count of how many parameter bytes
* have been read into the escape buffer
*/
extern char char_cnt;
/* the code being checked for in
* reassignment routines; if null, it is
* used to find an ununsed buffer; if
* the value is non zero and positive,
* it is used to look up a regular key;
* if non-zero and negative, it is used
* to look up an extended key */
extern int keycheck;
/* the parameter buffer for ansi escape
* sequences */
extern char esc_buf [ BUF_LEN ];
/* the current position */
extern POSITION curr;
/* the maximum position. Actually, the
* maximum line number is not used as
* a maximum, but is used simply to
* tell the clear-screen and
* clear-to-end-of-line code how much screen to
* clear */
extern POSITION max;
/* the current video page number */
extern char cur_page;
/* the current video address. this is
* the base address plus the offset to
* the current page */
extern char far *video_address;
/* the transfer address specified in the
* request header */
extern char far *transfer;
/* the count specified in the request
* header */
extern int count;
/*
* pointer to the request headerd
*/
extern struct
{
char rlength;
char units;
char command;
unsigned status;
char reserved [ 8 ];
char data;
char far *transfer;
unsigned count;
} far *rh;
extern int k; /* generic int */
/* pointer to the length field
* for the selected buffer */
extern char *len;
/* pointer to the definition
* field for the selected buffer */
extern char *ptr;
extern KEY kbuffer[NKEYS]; /* the buffers */
extern KEY *kp; /* pointer to a buffer */
/* r_buf[ r_index ] is the
* next byte to be read */
extern unsigned r_index;
/* r_buf[ w_index ] is where
* the next-byte can be written */
extern unsigned w_index;
extern char r_buf [ RLEN ]; /* ring buffer */
/*
* a temporary variable for storing either the delimiter while
* the escape sequence is in the IN_STRING state, or the value
* being computed if the escape sequence is in the IN_NUMBER
* state. a convenient way of doubling the utility of a byte
* of storage while keeping track of just what we're doing
* with it.
*/
extern union
{
char delim;
char value;
} tmp;
extern char state; /* the escape sequence state */
extern POSITION saved; /* the saved cursor position */
extern char wrap; /* wrap flag: wrap on if set */
extern char *cur_val; /* line or column parameter being
manipulated by w_cursor() */
extern char delta; /* incr/decr to cur_val */
extern char limit; /* limit of *cur_val */
