Instant interrupts

' Save ALL the compiler's SYSTEM variables and selected SFR registers before an interrupt, then restore them
'
' This allows a greater subset of BASIC commands within an interrupt handler
'
' For 16-bit core (18F) devices only. Using PROTON+ Version 3.03 Onwards.
'
' This program can be tested using the PIC18_ALCD_VHB file in the ISIS simulator.
'
Include "PROTON18_4.INC" ' Use the PROTON Dev board for the demonstration

REMINDERS = OFF
RESERVE_RAM 127 ' Reserve enough RAM at top of memory for a worse case scenario of ALL BANKA being used for system variables
REMINDERS = On

Dim COUNTS As Word SYSTEM
Dim COUNTS2 As Word SYSTEM

Symbol TIMER1 = TMR1L.Word ' Create a WORD variable from two hardware registers
Symbol TMR1IF = PIR1.0
Symbol GIE = INTCON.7

ON_HARDWARE_INTERRUPT GoTo INTERRUPT_HANDLER ' Point the interrupt vector to the subroutine "INTERRUPT_HANDLER"
'------------------------------------------------------------------------------------------------------
DelayMS 200 ' Wait for things to stabilise
GoTo OVER_INTERRUPT ' Jump over the interrupt subroutine

'------------------------------------------------------------------------------------------------------
' Macro to save the compiler's SYSTEM variables and selected SFR registers
SYSTEM_SAVE MACRO-
ASM-
; Context SAVE the essential registers
movff STATUS,_RAM_END ; Save the STATUS register
movff WREG,_RAM_END - 1 ; Save the WREG
movff BSR,_RAM_END - 2 ; Save the bank select register
movff FSR0L,_RAM_END - 3 ; Save low byte of FSR0
movff FSR0H,_RAM_END - 4 ; Save high byte of FSR0
movff FSR1L,_RAM_END - 5 ; Save low byte of FSR1
movff FSR1H,_RAM_END - 6 ; Save high byte of FSR1
movff FSR2L,_RAM_END - 7 ; Save low byte of FSR2
movff FSR2H,_RAM_END - 8 ; Save high byte of FSR2
movff PRODL,_RAM_END - 9 ; Save the multiply registers
movff PRODH,_RAM_END - 10 ; These require saving because the compiler uses them regularly.
movff TBLPTRL,_RAM_END - 11 ; Save the Table Pointer registers
movff TBLPTRH,_RAM_END - 12 ; These require saving because the compiler uses them regularly.
movff TABLAT,_RAM_END - 13 ; Save the code memory access register

; Save the compiler's SYSTEM variables
lfsr 0,_RAM_END - 14 ; Point FSR0 to the next available piece of memory in high RAM
lfsr 1,_SYSTEM_VARIABLE_COUNT - 1 ; Point FSR1 to the end of the SYSTEM variables in Access RAM
movlw _SYSTEM_VARIABLE_COUNT ; Form a loop for the amount of system variables used
movff POSTDEC1,POSTDEC0 ; Move the compiler's SYSTEM variables from Access RAM into high memory
decfsz WREG,F ; Decrement and skip if zero the variable counter
bra $ - 6 ; Keep placing variables until all done
VARIABLE _RAM_POINTER = (_RAM_END - 14) - _SYSTEM_VARIABLE_COUNT ; Point to the finishing point of the variable save
ENDASM-
ENDM
'------------------------------------------------------------------------------------------------------
' Macro to restore the compiler's SYSTEM variables and selected SFR registers
SYSTEM_RESTORE MACRO-
ASM-
; Restore the compiler's SYSTEM variables
lfsr 0,_RAM_END - 14 ; Point FSR0 to the start of the system variables stored in high memory
lfsr 1,_SYSTEM_VARIABLE_COUNT - 1 ; Point FSR1 to the end of the SYSTEM variables in Access RAM
movlw _SYSTEM_VARIABLE_COUNT ; Form a loop for the amount of system variables used
movff POSTDEC0,POSTDEC1 ; Move the compiler's SYSTEM variables from high memory into Access RAM
decfsz WREG,F ; Decrement and skip if zero the variable counter
bra $ - 6 ; Keep placing variables until all done

; Context RESTORE the essential registers and exit the interrupt
movff _RAM_END - 13,TABLAT ; Restore the TABLAT register
movff _RAM_END - 12,TBLPTRH ; Restore high byte of TBLPTR
movff _RAM_END - 11,TBLPTRL ; Restore low byte of TBLPTR
movff _RAM_END - 10,PRODH ; Restore high byte of PROD
movff _RAM_END - 9,PRODL ; Restore low byte of PROD
movff _RAM_END - 8,FSR2H ; Restore high byte of FSR2
movff _RAM_END - 7,FSR2L ; Restore low byte of FSR2
movff _RAM_END - 6,FSR1H ; Restore high byte of FSR1
movff _RAM_END - 5,FSR1L ; Restore low byte of FSR1
movff _RAM_END - 4,FSR0H ; Restore high byte of FSR0
movff _RAM_END - 3,FSR0L ; Restore low byte of FSR0
movff _RAM_END - 2,BSR ; Restore the bank select register
movff _RAM_END - 1,WREG ; Restore the WREG
movff _RAM_END,STATUS ; Restore the STATUS register
ENDASM-
ENDM
'------------------------------------------------------------------------------------------------------
' Interrupt service routine
INTERRUPT_HANDLER:
SYSTEM_SAVE ' Save the SYSTEM variables and selected SFR registers
RESET_BANK ' Reset the RAM banks first so we know where we are in RAM
'
' The body of the Interrupt routine goes here
'
Print At 2,1, "INTERRUPT ",Dec COUNTS2," " ' Display an incrementing counter on the LCD
Inc COUNTS2 ' Increment the counter

SYSTEM_RESTORE ' Restore the SYSTEM variables and selected SFR registers
Clear TMR1IF ' Clear the Timer1 interrupt flag
retfie ' Exit the interrupt
RESET_BANK ' Reset the RAM banks so the main program knows where it is in RAM
'------------------------------------------------------------------------------------------------------
' The MAIN DEMO PROGRAM LOOP STARTS HERE
OVER_INTERRUPT:

Cls ' Clear the LCD
COUNTS = 0 ' \
COUNTS2 = 0 ' / Reset the two counting variables

GIE = 0 ' Disable All Interrupts for now
T1CON = %00000001 ' Turn on Timer1, prescaler = 1:1
PIR1.0 = 0 ' Clear TMR1 interrupt flag
PIE1.0 = 1 ' Enable TMR1 as peripheral interrupt source
INTCON = %11000000 ' Enable global interrupts and peripheral interrupts

While 1 = 1 ' Create an infinite loop
PIE1.0 = 0 ' Disable the TMR1 interrupt while we print in the foreground
Print At 1,1,"FOREGROUND ",Dec COUNTS," " ' Display an incrementing counter on the LCD
PIE1.0 = 1 ' Re-enable the TMR1 interrupt
Inc COUNTS
DelayMS 300
Wend