'*************************************************** ' IRQ coding for midi-in * ' by * ' Godfried-Willem Raes * ' Version 2.8 * '*************************************************** ' Interrupt-driven serial buffer for USART MIDI receive using a hardware high priority interrupt. ' 08.10.2025 - Version for the robot ' 05.08.2026: adapting for ' 20.10.2026: adapted for ' Create the SYSTEM variables and aliases for the Buffered commands Dim PP0 As Byte System ' \ Dim PP0H As Byte System ' / Storage for FSR0L\H registers Dim FSR0SaveInt As PP0 ' alias Dim FSR0SaveIntH As PP0H ' alias Dim USART_FSR0_Save As FSR0SaveInt.Word ' Alias the FSR0L\H storage to PP0\H Dim USART_FSR1_Save As Word System ' Storage for FSR1L\H registers Dim USART_FSR0 As FSR0L.Word ' alias Dim USART_FSR1 As FSR1L.Word ' alias Dim IndexIn As Byte System ' Pointer to the next empty location in the buffer Dim IndexOut As Byte System ' Pointer to the location of the oldest character in the buffer Reminders = On Warnings = On ' Point to the high priority hardware interrupt handler On_Hardware_Interrupt GoTo High_Prior_Interrupt On_Low_Interrupt GoTo Low_Prior_Interrupt GoTo _Over_IRQ_Handler ' Jump over the subroutines High_Prior_Interrupt: _Timer0_IRQ: If INTCONbits_T0IF = 1 Then Clear INTCONbits_T0IF ' Clear the Timer0 Overflow flag Inc Cnt.Word1 ' would it be slower to do Inc Cnt.Word1 instead of CntHw here? Cnt.Word0 = CntLw ' 08.12.2019 Btg Debug_Led ' asm bit toggle - debug led watchdog.Port must be set to output!!! Retfie Fast EndIf _UART_IRQ: If PIR1bits_RCIF = 1 Then ' Was it a USART1 byte Receive that triggered the interrupt ? Movlw 6 ' Yes. So Mask out unwanted bits Andwf RCSTA,w ' Check for errors Bnz _Uart_Error ' Was either error status bit set? USART_FSR1_Save = USART_FSR1 ' Save FSR1L\H registers Inc IndexIn ' Move up the buffer index (0-255) ' if the buffer is smaller, but still a power of 2, we can 'implement circularity simply as: 'IndexIn = IndexIn & ~USART_Buffersize 'or, if it's faster, mask the highest limit bit: 'Clear IndexIn.7 = for a 128 byte buffer 'Clear IndexIn.6 = for a 64 byte buffer USART_FSR1 = VarPtr Ringbuffer ' Point FSR1L\H to _USART_RingBuffer USART_FSR1 = USART_FSR1 + IndexIn ' Add the buffer position to FSR1L\H INDF1 = RCREG ' Place the received character into the buffer USART_FSR1 = USART_FSR1_Save ' Restore FSR1L\H registers 'Toggle PORTB.5 'debug - checked. This works. Retfie Fast ' Exit from the interrupt, restoring the WREG, STATUS, and BSR registers _Uart_Error: WREG = RCREG ' empty the 2 byte UART buffer WREG = RCREG Clear RCSTAbits_CREN ' Clear receiver status Set RCSTAbits_CREN EndIf Retfie Fast Proc GetMidiIn (), Byte If IndexIn <> IndexOut Then Inc IndexOut ' Increment IndexOut pointer (0 to 255) USART_FSR0_Save = USART_FSR0 ' Save FSR0L\H registers USART_FSR0 = VarPtr Ringbuffer ' Point FSR0L\H to Ringbuffer USART_FSR0 = USART_FSR0 + IndexOut ' Add the buffer position to FSR0L\H WREG = INDF0 ' Read buffer location (IndexOut) into WREG Result = WREG ' return it in the function USART_FSR0 = USART_FSR0_Save ' Restore FSR0\H registers Set STATUSbits_C ' Set CARRY flag to indicate a byte received Ret ' compulsary here! Else WREG = 255 Result = WREG Btfss STATUS,C ' Return with the CARRY flag clear to indicate timed out Ret 'compulsary here EndIf EndProc Proc Init_Usart_Interrupt () Clear IndexIn ' Clear the buffer internal pointer Clear IndexOut ' Clear the buffer external pointer Set PIE1bits_RCIE ' Enable interrupt on USART1 receive #ifdef __Low_Interrupts_Enabled ' Are we using low priority interrupts as well ? Set IPR1bits_RCIP ' Yes. So USART1 Receive Interrupt to High priority #endif Set INTCONbits_GIE ' enable general interrups Set INTCONbits_PEIE ' Enable global and peripheral interrupts 'Set INTCONbits_T0IE ' Enable Timer0 overflow interrupt, done on opentimer0() EndProc Proc Clear_Serial_Buffer () PIE1bits_RCIE = 0 ' Disable interrupt on USART1 receive Clear Ringbuffer ' Clear the serial buffer Clear IndexIn ' Clear the buffer internal pointer Clear IndexOut ' Clear the buffer external pointer Set PIE1bits_RCIE ' Re-Enable interrupt on USART1 receive EndProc '-------------------------------------------------------------------------------- ' Initialise the USART1 interrupt ' Input : None ' Output : None ' Notes : Enables interrupt on USART1 receive. ' : Enables global and peripheral interrupts ' : If Prioritised interrupts are used, the USART interrupt priority is made high '$define InitUSARTInterrupt () Init_Usart_Interrupt 'added 31.08.2010 gwr 'Init_Usart_Interrupt Macro ' GoSub _Init_Usart ' Endm '#ifdef Init_Usart_Interrupt#Req '_Init_Usart: ' Clear IndexIn ' Clear the buffer internal pointer ' Clear IndexOut ' Clear the buffer external pointer ' Set PIE1bits_RCIE ' Enable interrupt on USART1 receive ' #ifdef __Low_Interrupts_Enabled ' Are we using low priority interrupts as well ? ' Set IPR1bits_RCIP ' Yes. So USART1 Receive Interrupt to High priority ' #endif ' Set INTCONbits_GIE ' enable general interrups ' Set INTCONbits_PEIE ' Enable global and peripheral interrupts ' 'Set INTCONbits_T0IE ' Enable Timer0 overflow interrupt, done on opentimer0() ' Return '#endif '-------------------------------------------------------------------------------- ' Clear the Serial Buffer ' Input : None ' Output : None ' Notes : Also resets the index pointers to the serial buffer '$define ClearSerialBuffer () Clear_Serial_Buffer ' added 31.08.2010 - gwr 'Clear_Serial_Buffer Macro ' GoSub _Clear_Usart_Buffer ' Endm '#ifdef Clear_Serial_Buffer#Req '_Clear_Usart_Buffer: ' PIE1bits_RCIE = 0 ' Disable interrupt on USART1 receive ' Clear Ringbuffer ' Clear the serial buffer ' Clear IndexIn ' Clear the buffer internal pointer ' Clear IndexOut ' Clear the buffer external pointer ' Set PIE1bits_RCIE ' Re-Enable interrupt on USART1 receive ' Return '#endif '------------------------------------------------------- ' Low Priority Interrupt on Timer3 overflow Low_Prior_Interrupt: Timer3_ISR: ' for we use this timer for motor control ' for we can use it for lite automation. Context Save ' Save the contents of WREG, STATUS, and BSR Clear PIR2bits_TMR3IF ' Clear the Timer3 interrupt flag. Clear Tim3 If CC69 > 0 Then If NrLowNotes = 0 Then Clear Lite120 Else Set Lite120 EndIf If NrHighNotes = 0 Then Clear Lite122 Else Set Lite122 EndIf EndIf Context Restore ' Restore the contents of WREG, STATUS, and BSR, then exit interrupt '------------------------------------------------------- _Over_IRQ_Handler: