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common.h
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common.h
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/*
Main definitions file for MegaDrive++ R
Copyright (C) 2018-2019 pcm720 <[email protected]>
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see
<http://www.gnu.org/licenses/>.
*/
#ifndef COMMON_H_
#define COMMON_H_
#include <avr/io.h>
#include <util/delay.h>
// Undefine for Mega Drives with active high reset (VA5 and lower (?))
#define RESET_ACTIVE_LOW
// Amount of (seconds - 1) to monitor the combo for before switching the region or resetting the console
#define LENGTH_COMBO 1
// Amount of (seconds - 1) to monitor reset button for
#define LENGTH_RESET 2
// Pad button status map: S A C B R L D U, button is 0 if pressed
#define COMBO_RESET 0x0F // Start + A + B + C / ~(11110000)
#define COMBO_SAVE 0x0B // Left + Start + A + B + C / ~(11110100) | Saves current region to EEPROM
#define COMBO_USA 0x3B // Left + Start + A / ~(11000100)
#define COMBO_EUR 0x6B // Left + Start + B / ~(10010100)
#define COMBO_JAP 0x5B // Left + Start + C / ~(10100100)
#define COMBO_USA_RESET 0x37 // Right + Start + A / ~(11001000)
#define COMBO_EUR_RESET 0x67 // Right + Start + B / ~(10011000)
#define COMBO_JAP_RESET 0x57 // Right + Start + C / ~(10101000)
#define COMBO_OFF 0x00 // To use when no combo is currently active, don't change this
// Pins: LANGUAGE VIDEOMODE
// USA: HIGH HIGH
// EUR: HIGH LOW
// JAP: LOW HIGH
#define JAP 0x1 // 01
#define EUR 0x2 // 10
#define USA 0x3 // 11
#define NXT 0x4 // Next region
#define DEFAULT_REGION USA // Default region to use if EEPROM read fails or if this is first boot
// End of configurable area
#ifdef RESET_ACTIVE_LOW
#define PINB_RESET ~PINB
#else
#define PINB_RESET PINB
#endif
#endif
/*
* Pin assignments:
* PORT B:
* PORTB Map: 76XXX210
* NTSC_LED PB0 (OUT)
* JAP_LED PB1 (OUT)
* PAD_DBG_LED PB2 (OUT)
* MD_RESET_IN PB6 (IN) [UNUSED]
* MD_RESET_OUT PB7 (IN/OUT)
*
* PORT C:
* PORTC Map: XXXXXX10
* NTSC PC0 (OUT)
* JAP PC1 (OUT)
*
* PORT D:
* PORTD Map: X6543210 / All are inputs except PD7
* MD_PAD_UP PD0 (Pad Pin 1 / UP)
* MD_PAD_DOWN PD1 (Pad Pin 2 / DOWN)
* MD_PAD_LEFT PD2 (Pad Pin 3 / LEFT)
* MD_PAD_RIGHT PD3 (Pad Pin 4 / RIGHT)
* MD_PAD_TL PD4 (Pad Pin 6 / A/B)
* MD_PAD_TR PD5 (Pad Pin 9 / Start/C)
* MD_PAD_TH PD6 (Pad Pin 7 / SELECT)
*
* Some technical notes on Mega Drive gamepads:
*
* 3-button pad:
* State Select(TH) Up Down Left Right TL TR
* 0 HIGH Up Down Left Right B C
* 1 LOW Up Down LOW LOW A Start
*
* 6-button pad:
* State Select(TH) Up Down Left Right TL TR
* 0 HIGH Up Down Left Right B C
* 1 LOW Up Down LOW LOW A Start
* 2 HIGH Up Down Left Right B C
* 3 LOW Up Down LOW LOW A Start
* 4 HIGH Up Down Left Right B C
* 5 LOW LOW LOW LOW LOW A Start
* 6 HIGH Z X Y Mode B C
* 7 LOW - - - - A Start
*
* Notes:
* 1. Select idles in HIGH state in official games
* Unlicensed stuff like Everdrive and chinese multicarts actually read pads incorrectly, leaving Select pulled down after reading.
* We need to consider every option.
* 2. For 3-button mode, Select pulse length is 6-6.5 us;
* For 6-button mode, Select period (Tsel) is non-uniform and depends on the game.
* For Street Fighter 2, select cycle looks like this:
* Select is active high
* first select pluse (to LOW state) is 25 us
* second (HIGH) is 4.7-5 us
* third (LOW) is 8-9 us
* fourth (HIGH) is 4.7-5 us
* fifth (LOW) is 9-11 us
* sixth (HIGH) is 4.7-5 us
* seventh (LOW) is 25 us
* For Streets of Rage 3:
* Select is active high
* first select pluse (to LOW state) is 10 us
* second (HIGH) is 6.2 us
* third (LOW) is 7.3 us
* fourth (HIGH) is 6.25 us
* fifth (LOW) is 7.3 us
* sixth (HIGH) is 6.25 us
* seventh (LOW) is 7 us
* 3. 6-button Select cycle length is around 50-100 us (50 for Streets of Rage 3, 84 for Street Fighter 2)
* 4. Pad internal reset (Tres) is 2 ms (according to SEGA specifications on 6-button pad)
* 5. Some 3-button pad-only games pulse Select line multiple times in 2 ms interval, triggering 6-button pad to output more than two states.
* For example, Ms. Pac-Man pulses Select line thrice in 100 us interval. This behaviour is considered incorrect.
* We can skip these pulses by delaying for more than 100 us after the first level change.
* 6. It takes ~200-600 ns for 6-button pad to update its output after Select level change
* 7. Frame period is 16.67 ms for NTSC and 20 ms for PAL
* 8. Since we don't really need to read all buttons of 6-button pad, we can pretend that it doesn't exist
*/