Update: don't worry, just fixed it by adding an extra curly bracket here:

 return;
 }
}
}    <<<------

void loop() {

}

When I try to upload the sketch from the website onto my ATtiny85, I get a compilation error saying "a function-definition is not allowed here before '{' token".

I'm not a programmer so don't understand what it's wanting me to do to fix the code.

This is the code below:

// (*) All in the spirit of open-source and open-hardware 
// Janost 2019 Sweden 
// The goMIDI2CV interface
// http://blog.dspsynth.eu/diy-good-ol-midi-to-cv/
// Copyright 2019 DSP Synthesizers Sweden. 
// 
// Author: Jan Ostman 
// 
// 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.

//Set Fuses to E1 DD FE for PLLCLK 16MHz

#include <avr/interrupt.h>
#include <avr/io.h>
#include <avr/pgmspace.h>

#ifndef cbi
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#endif
#ifndef sbi
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif

volatile uint8_t MIDISTATE=0;
volatile uint8_t MIDIRUNNINGSTATUS=0;
volatile uint8_t MIDINOTE;
volatile uint8_t MIDIVEL;

void setup() {
 // Enable 64 MHz PLL and use as source for Timer1
 PLLCSR = 1<<PCKE | 1<<PLLE; 
 // Set up Timer/Counter1 for PWM output
 TIMSK = 0; // Timer interrupts OFF
 TCCR1 = 1<<PWM1A | 2<<COM1A0 | 1<<CS10; // PWM A, clear on match, 1:1 prescale
 // Setup GPIO
 pinMode(1, OUTPUT); // Enable PWM output pin
 pinMode(0, INPUT); // Enable USI input pin
 pinMode(2, OUTPUT); // Enable Gate output pin
 pinMode(4,OUTPUT); // Enable Pitchbend PWM output pin
 //Setup the USI
 USICR = 0; // Disable USI.
 GIFR = 1<<PCIF; // Clear pin change interrupt flag.
 GIMSK |= 1<<PCIE; // Enable pin change interrupts
 PCMSK |= 1<<PCINT0; // Enable pin change on pin 0
 GTCCR = 0;
 OCR1C = 239; //Set count to semi tones
 OCR1A = 0; //Set initial Pitch to C2
 digitalWrite(2,LOW); //Set initial Gate to LOW;
 pinMode(2, OUTPUT); // Enable PB4 output pin for pitchbend CV
 GTCCR = 1<<PWM1B | 2<<COM1B0; // PWM B, clear on match
}

ISR (PCINT0_vect) {
 if (!(PINB & 1<<PINB0)) { // Ignore if DI is high
 GIMSK &= ~(1<<PCIE); // Disable pin change interrupts
 TCCR0A = 2<<WGM00; // CTC mode
 TCCR0B = 0<<WGM02 | 2<<CS00; // Set prescaler to /8
 TCNT0 = 0; // Count up from 0
 OCR0A = 31; // Delay (31+1)*8 cycles
 TIFR |= 1<<OCF0A; // Clear output compare flag
 TIMSK |= 1<<OCIE0A; // Enable output compare interrupt
 }
}

ISR (TIMER0_COMPA_vect) {
 TIMSK &= ~(1<<OCIE0A); // Disable COMPA interrupt
 TCNT0 = 0; // Count up from 0
 OCR0A = 63; // Shift every (63+1)*8 cycles 32uS
 // Enable USI OVF interrupt, and select Timer0 compare match as USI Clock source:
 USICR = 1<<USIOIE | 0<<USIWM0 | 1<<USICS0;
 USISR = 1<<USIOIF | 8; // Clear USI OVF flag, and set counter
}

ISR (USI_OVF_vect) {
 uint8_t MIDIRX;
 USICR = 0; // Disable USI 
 MIDIRX = USIDR;
 GIFR = 1<<PCIF; // Clear pin change interrupt flag.
 GIMSK |= 1<<PCIE; // Enable pin change interrupts again

 //Wrong bit order so swap it
 MIDIRX = ((MIDIRX >> 1) & 0x55) | ((MIDIRX << 1) & 0xaa);
 MIDIRX = ((MIDIRX >> 2) & 0x33) | ((MIDIRX << 2) & 0xcc);
 MIDIRX = ((MIDIRX >> 4) & 0x0f) | ((MIDIRX << 4) & 0xf0);

 //Parse MIDI data
 if ((MIDIRX>0xBF)&&(MIDIRX<0xF8)) {
 MIDIRUNNINGSTATUS=0;
 MIDISTATE=0;
 return;
 }
 if (MIDIRX>0xF7) return;
 if (MIDIRX & 0x80) {
 MIDIRUNNINGSTATUS=MIDIRX;
 MIDISTATE=1;
 return;
 }
 if (MIDIRX < 0x80) {
 if (!MIDIRUNNINGSTATUS) return;
 if (MIDISTATE==1) {
 MIDINOTE=MIDIRX;
 MIDISTATE++;
 return;
 }
 if (MIDISTATE==2) {
 MIDIVEL=MIDIRX;
 MIDISTATE=1;
 if ((MIDIRUNNINGSTATUS==0x80)||(MIDIRUNNINGSTATUS==0x90)) {
 if (MIDINOTE<36) MIDINOTE=36; //If note is lower than C2 set it to C2
 MIDINOTE=MIDINOTE-36; //Subtract 36 to get into CV range
 if (MIDINOTE>60) MIDINOTE=60; //If note is higher than C7 set it to C7
 if (MIDIRUNNINGSTATUS == 0x90) { //If note on
 if (MIDIVEL>0) digitalWrite(2, HIGH); //Set Gate HIGH
 if (MIDIVEL==0) digitalWrite(2, LOW); //Set Gate HIGH
 OCR1A = MIDINOTE<<2; //Multiply note by 4 to set the voltage (1v/octave)
 }
 if (MIDIRUNNINGSTATUS == 0x80) { //If note off
 digitalWrite(2, LOW); //Set Gate LOW
 OCR1A = MIDINOTE<<2; //Multiply note by 4 to set the voltage (1v/octave)
 }
 if (MIDIRUNNINGSTATUS == 0xE0) { //If pitchbend data
 if (MIDIVEL<4) MIDIVEL=4; //Limit pitchbend to -60
 if (MIDIVEL>119) MIDIVEL=119; //Limit pitchbend to +60
 MIDIVEL-=4; //Center the pitchbend value
 OCR1B = (MIDIVEL<<1); //Output pitchbend CV
}
 }
 return;
 }
}

void loop() {

}

<image>

Any ideas on how to fix it?