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/*********************************  getch_light.as ****************************

* Author:        Agner Fog

* date created:  2021-05-25

* Last modified: 2021-05-25

* Version:       1.11

* Project:       ForwardCom library libc_light.li

* Description:   Common C functions: _kbhit, getch, getche

*                Nonstandard function: getch_nonblocking

*

* This version is for small CPUs with limited capabilities

* The following instructions are avoided: mul, div, push, pop, sys_call.

* Input comes directly from input port 8

* Output to stdout goes directly to output port 10

*

* The functions _kbhit, getch, getche are common, but not part of the official C standard.

* getch_nonblocking is my own invention. It is sadly missing in common systems

*

* C declarations:

* int _kbhit(void);

* int getch(void);

* int getche(void);

* int getch_nonblocking(void);

*

* Description:

* _kbhit:   return 1 if there is at least one character in the input buffer, 0 if buffer empty

* getch:    waits for input from stdin. returns one character

* getche:   same as getch. The input is echoed to the standard output

* getch_nonblocking: reads one character from stdin without waiting. returns -1 if the input buffer is empty

*

* Copyright 2021 GNU General Public License http://www.gnu.org/licenses

*****************************************************************************/

// define input and output ports

%stdin_port = 8

%stdin_status_port = 9

%stdout_port = 10

code section execute

// _kbhit function

// returns 0 if there is no input

// returns 1 if the standard input input buffer contains at least one character

_kbhit function public reguse = 1,0

__kbhit function public reguse = 1,0

  int r0 = input(r0, stdin_status_port)// read status port

  int16 r0 = r0 != 0                   // bit 0-15 = number of bytes in input buffer

  return

// _getch function

// waits for input from standard input. returns one character in the interval 0 - 0xFF

// no error checking

_getch function public reguse = 1,0

  do {                                 // keep reading until input data valid

    int r0 = input(r0, stdin_port)     // read from input port

  }

  while (int !(r0 & 0x100));           // bit 8 = data valid

  int8 r0 = r0                         // isolate bit 0-7

  return

// _getche function

// same as _getch

// echoes character to standard output

_getche function public reguse = 1,0

  do {                                 // keep reading until input data valid

    int r0 = input(r0, stdin_port)     // read from input port

  }

  while (int !(r0 & 0x100));           // bit 8 = data valid

  int8 r0 = r0                         // isolate bit 0-7

  int output(r0, r0, stdout_port)      // output the same character

  return

// _getch_nonblocking function

// reads input from standard input. Does not wait for input

// returns one character in the interval 0 - 0xFF if input available

// returns -1 if input buffer empty

// future implementations may return other negative values in case of error

_getch_nonblocking function public reguse = 1,0

  int r0 = input(r0, stdin_port)       // read from input port

  if (int (r0 & 0x100)) {              // bit 8 = data valid

    int8 r0 = r0                       // isolate bit 0-7

    return

  }

  int r0 = -1                          // input buffer empty. return -1

  return

code end