#ifndef _MC6840_H_
#define _MC6840_H_

#include <inttypes.h>

#define MC6840_CON13    (*(volatile uint8_t*)0x6480)
#define MC6840_CON2    (*(volatile uint8_t*)0x6481)
#define MC6840_STATUS    (*(volatile uint8_t*)0x6481)
#define MC6840_TIMER1    (*(volatile uint16_t*)0x6482)
#define MC6840_TIMER2    (*(volatile uint16_t*)0x6484)
#define MC6840_TIMER3    (*(volatile uint16_t*)0x6486)

#define Swap2Bytes(val) \
 ( (((val) >> 8) & 0x00FF) | (((val) << 8) & 0xFF00) )

#define TM_COUNTER_OUTPUT_ENABLE      0x80
#define TM_COUNTER_OUTPUT_DISABLE      0x00

#define TM_INTERUPT_ENABLE            0x40
#define TM_INTERUPT_DISABLE            0x00

#define TM_CONT_OP_MODE1            0x00
#define TM_FREQ_COMP_MODE1            0x20
#define TM_CONT_OP_MODE2            0x10
#define TM_PUSE_WIDTH_COMP_MODE2      0x30
#define TM_SINGLE_SHOT_MODE1         0x08
#define TM_FREQ_COMP_MODE2            0x28
#define TM_SINGLE_SHOT_MODE2         0x18
#define TM_PULSE_WIDTH_COMP_MODE2      0x38

#define TM_NORMAL_16BIT               0x00
#define TM_DUAL_8BIT               0x04

#define TM_EXT_CLK                  0x00
#define TM_SYS_CLK                  0x02

#define TMCR1_ALL_TIMERS_ALLOWED      0x00
#define TMCR1_ALL_TIMERS_PRESET         0x01

#define TMCR2_WRITE_CR3               0x00
#define TMCR2_WRITE_CR1               0x01

#define TMCR3_T3_CLK_NO_PRESCALER      0x00
#define TMCR3_T3_CLK_DIV8_PRESCALER      0x01


void m6840_init (void);
uint32_t millis(void);
uint32_t uptime(void);
uint16_t get_geiger_pulses (void);
void set_sound_frequency (uint16_t freq);

#endif //_MC6840_H_

#include <6502.h>
#include "mc6840.h"
#include "ff.h"

volatile uint32_t milliseconds = 0;
volatile uint32_t uptime_value = 0;
volatile uint8_t  geiger_ind = 0;
volatile uint16_t geiger_pulses[60];
volatile uint8_t  geiger_ovf = 0;

uint32_t tmp;
uint8_t i;

void m6840_init (void) {
    MC6840_CON13 = TM_COUNTER_OUTPUT_DISABLE | TM_INTERUPT_ENABLE | TM_CONT_OP_MODE1 | TM_NORMAL_16BIT | TM_SYS_CLK | TMCR3_T3_CLK_NO_PRESCALER;   //CON3 first by default after reset. TIMER3 is used for systick. Output diable and sys clk.
    MC6840_CON2 = TM_COUNTER_OUTPUT_ENABLE | TM_INTERUPT_DISABLE | TM_CONT_OP_MODE1 | TM_NORMAL_16BIT | TM_SYS_CLK | TMCR2_WRITE_CR1;            //CON2 accessed directly. TIMER2 generates sound. Output enable and sys clk.
    MC6840_CON13 = TM_COUNTER_OUTPUT_DISABLE | TM_INTERUPT_DISABLE | TM_CONT_OP_MODE1 | TM_NORMAL_16BIT | TM_EXT_CLK | TMCR1_ALL_TIMERS_ALLOWED;   //CON1. TIMER1 counts Geiger pulses, so external source
    MC6840_TIMER1 = Swap2Bytes(0xFFFF);       //Remember about endianess - MC6800 family is big endian, 6502 is little endian. Remember that timer is decremented.
    MC6840_TIMER2 = Swap2Bytes(0x07D0);       //500 Hz signal on audio output
    MC6840_TIMER3 = Swap2Bytes(0x03E8);       //1ms interrupt
   
    for (i=0; i<60; i++) geiger_pulses[i] = 0x00;
}

DWORD get_fattime (void)
{
   return(0);
}

uint32_t millis(void) {
    CLI();
    tmp = milliseconds;
    SEI();
   return tmp;
}

uint32_t uptime (void) {
   CLI();
   tmp = uptime_value;
   SEI();
   return tmp;
}

void update_geiger_pulses (void) {
    CLI();
    geiger_pulses[geiger_ind] = 0xFFFF - Swap2Bytes(MC6840_TIMER1);
    SEI();
    geiger_ind++;
    if (geiger_ind > 59) geiger_ind = 0;
}

uint16_t get_geiger_pulses (void) {
   for (i=0; i<60; i++) tmp += geiger_pulses[i];
    return tmp/60;
}


void set_sound_frequency (uint16_t freq) {
    if (freq < 24) return;          //Min required frequency. It will solve div/0 and word size issues.
    MC6840_TIMER2 = Swap2Bytes(1000000/freq);
}

; ---------------------------------------------------------------------------
; interrupt.s
; ---------------------------------------------------------------------------
;
; Interrupt handler.
;
; Checks for a BRK instruction and returns from all valid interrupts.

.import   _init, _milliseconds, _geiger_ovf, _uptime_value
.import   _update_geiger_pulses
.export   _irq_int, _nmi_int

MC6840_STA     = $6481
M6242_STA     = $640D
MC6840_TIMER1 = $6482
MC6840_TIMER3 = $6486

.segment  "CODE"

.PC02                             ; Force 65C02 assembly mode

; ---------------------------------------------------------------------------
; Non-maskable interrupt (NMI) service routine

_nmi_int:  RTI                    ; Return from all NMI interrupts

; ---------------------------------------------------------------------------
; Maskable interrupt (IRQ) service routine

_irq_int:  PHX                    ; Save X register contents to stack
           TSX                    ; Transfer stack pointer to X
           PHA                    ; Save accumulator contents to stack
           INX                    ; Increment X so it points to the status
           INX                    ;   register value saved on the stack
           LDA $100,X             ; Load status register contents
           AND #$10               ; Isolate B status bit
           BNE break              ; If B = 1, BRK detected

; ---------------------------------------------------------------------------
; IRQ detected

irq_chk_t1:
           LDA MC6840_STA         ; Load MC6840 status register
           TAX                 ; Preserve A, it will be destroyed by AND
           AND #$01               ; Check if T1 interrupt flag is set
           BEQ irq_chk_t3         ; If flag is cleared, go to the next stage (check T3 interrupt flag)
           INC _geiger_ovf        ; Otherwise increment timer overflow variable
           LDA MC6840_TIMER1      ; You must read T1 to clear interrupt flag!!!
           LDA MC6840_TIMER1+1
irq_chk_t3:
         TXA                 ; Restore A that might have been destroyed by AND
           AND #$04               ; Check if T3 interrupt flag is set
           BEQ irq_chk_rtc        ; If flag is cleared, go to the next stage
           LDA MC6840_TIMER3      ; You must read T3 to clear interrupt flag
           LDA MC6840_TIMER3+1
           INC _milliseconds      ; Increment milliseconds variable
           BNE irq_chk_rtc
           INC _milliseconds+1
           BNE irq_chk_rtc
           INC _milliseconds+2
           BNE irq_chk_rtc
           INC _milliseconds+3
irq_chk_rtc:
           LDA M6242_STA          ; Load RTC status register
           AND #04                ; Check if IRQ flag is set
           BEQ irq_ret            ; If not, this is not RTC interrupt, co continue
           LDA #$00               ; Otherwise clear flag
           STA M6242_STA
           JSR _update_geiger_pulses ; goto the subroutine updating giger pulses
           INC _uptime_value      ; And increment uptime variable
           BNE irq_ret
           INC _uptime_value+1
           BNE irq_ret
           INC _uptime_value+2
           BNE irq_ret
           INC _uptime_value+3
           BNE irq_ret
irq_ret:   PLA                    ; Restore accumulator contents
           PLX                    ; Restore X register contents
           RTI                    ; Return from all IRQ interrupts

; ---------------------------------------------------------------------------
; BRK detected, stop

break:     JMP _init              ; If BRK is detected, something very bad
                                   ; has happened, restart

mos6551_puts("Millis: ");
ultoa(millis(), buffer, 10);
mos6551_puts(buffer);
mos6551_puts("\r\n");

    MC6840_TIMER1 = Swap2Bytes(0xFFFF);       //Remember about endianess - MC6800 family is big endian, 6502 is little endian. Remember that timer is decremented.
    MC6840_TIMER2 = Swap2Bytes(0x07D0);       //500 Hz signal on audio output
    MC6840_TIMER3 = Swap2Bytes(0x03E8);       //1ms interrupt