Adding a DOS port to run on x86 single board computer.
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skarg
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/**************************************************************************
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*
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* Copyright (C) 2007 Steve Karg <skarg@users.sourceforge.net>
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be included
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* in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*
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*********************************************************************/
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#include <stdint.h>
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#include <stdio.h>
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#include <dos.h>
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/* global variable counts milliseconds */
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volatile unsigned long Timer_Milliseconds;
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/* MS/TP Silence Timer */
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static volatile int SilenceTime;
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/* counts ticks */
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volatile unsigned long Timer_Milliseconds;
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#define RTC_CMD_ADDR 0x70 // RTC internal register offset goes here
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#define RTC_DAT_ADDR 0x71 // RTC internal register R/W access here
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static uint8_t RTC_RS_Convert(
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uint16_t hertz)
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{
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uint8_t RS = 0;
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/* from DS12887A datasheet
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SELECT BITS tPI PERIODIC
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REGISTER A INTERRUPT SQW OUTPUT
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RS3 RS2 RS1 RS0 RATE FREQUENCY
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--- --- --- --- ------------ ----------
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0 0 0 0 None 0Hz
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0 0 0 1 3.90625ms 256Hz
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0 0 1 0 7.8125ms 128Hz
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0 0 1 1 122.070µs 8192Hz
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0 1 0 0 244.141µs 4096Hz
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0 1 0 1 488.281µs 2048Hz
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0 1 1 0 976.5625µs 1024Hz
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0 1 1 1 1.953125ms 512Hz
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1 0 0 0 3.90625ms 256Hz
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1 0 0 1 7.8125ms 128Hz
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1 0 1 0 15.625ms 64Hz
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1 0 1 1 31.25ms 32Hz
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1 1 0 0 62.5ms 16Hz
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1 1 0 1 125ms 8Hz
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1 1 1 0 250ms 4Hz
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1 1 1 1 500ms 2Hz
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*/
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/* FIXME: create a clever formula to replace switch */
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switch (hertz) {
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case 8192: RS = 3; break;
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case 4096: RS = 4; break;
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case 2048: RS = 5; break;
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case 1024: RS = 6; break;
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case 512: RS = 7; break;
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case 256: RS = 8; break;
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case 128: RS = 9; break;
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case 64: RS = 10; break;
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case 32: RS = 11; break;
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case 16: RS = 12; break;
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case 8: RS = 13; break;
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case 4: RS = 14; break;
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case 2: RS = 15; break;
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default:
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break;
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}
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return RS;
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}
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/* setting for 8192 interrupts per second
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which is an interrupt every 122uS. */
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#define INT_FREQ 8192
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static void interrupt Timer_Interrupt_Handler(
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void)
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{
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static uint16_t Timer_Ticks = 0;
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static uint16_t Elapsed_Milliseconds = 0;
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uint16_t milliseconds = 0;
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uint16_t diff = 0;
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uint8_t temp_reg;
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Timer_Ticks++;
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milliseconds = (Timer_Ticks * 1000)/INT_FREQ;
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diff = milliseconds - Elapsed_Milliseconds;
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if (diff >= 1) {
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Elapsed_Milliseconds = milliseconds;
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Timer_Milliseconds++;
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if (SilenceTime < 60000)
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SilenceTime++;
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}
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/* max resolution */
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if (Timer_Ticks >= INT_FREQ) {
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Timer_Ticks = 0;
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Elapsed_Milliseconds = 0;
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}
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/* clear interrupt */
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outportb( RTC_CMD_ADDR, 0x0C ); // select RTC register C
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temp_reg = inportb( RTC_DAT_ADDR ); // read RTC register C
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/* signal end of interrupt to slave PIC */
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outportb( 0xA0, 0x20 );
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/* signal end of interrupt to master PIC */
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outportb( 0x20, 0x20 );
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}
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/* previous interrrupt vector */
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static void interrupt(*OldVector)();
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void Timer_Cleanup(void)
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{
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setvect(0x70,OldVector);
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}
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void Timer_Init(
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void)
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{
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uint8_t RC = RTC_RS_Convert(INT_FREQ);
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/* get old interrupt vector to re-install on exit */
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OldVector = getvect(0x70);
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/* disable interrupts */
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disable();
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/* set RTC int. vector for our routine */
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setvect(0x70,Timer_Interrupt_Handler);
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/* set register B with PIE enabled */
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outportb( RTC_CMD_ADDR, 0x0B );
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outportb( RTC_DAT_ADDR, 0x42 );
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/* set register A to our frequency */
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outportb( RTC_CMD_ADDR, 0x0A );
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outportb( RTC_DAT_ADDR, (0x20 | (RC & 0x0F)) );
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/* re-enable system interrupts */
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enable();
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atexit(Timer_Cleanup);
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}
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int Timer_Silence(
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void)
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{
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uint16_t time_value;
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disable();
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time_value = SilenceTime;
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enable();
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return time_value;
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}
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void Timer_Silence_Reset(
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void)
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{
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disable();
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SilenceTime = 0;
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enable();
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}
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