How we write our interrupt handler depends if we're running from RAM or ROM. Here We'll assume we're running from a ROM cartridge, as it's the harder method. The technique is almost identical for a RAM based interrupt handler though.

The video hardware can cause a VBLANK interrupt once per frame, but for this to happen we need to set bit 5 of VDP Register 1 to one. Otherwise no interrupts will occur and we won't get any sound!
IM1 causes a call to address &0038 on interrupt, If we're working on a system with 64k ram, we can page in RAM and put a JP at that address. Otherwise if we're running from cartridge we have to 'Chain onto' the firmware interrupt handler, we do this by writing a jump at address &FD9Ah
We should ensure IM1 is set, and enable interrupts to get things started.
Our interrupt handler updates the music. Note: As we're chaining onto the firmware routine, enabling interrupts and clearing the interrupt by reading the VDP status is done for us - we need to do this ourselves if we're writing our own complete interrupt handler
Reading in from the control port will mess up our address selection, if an interrupt occurs in between writing the H and L part of the address, to ensure this doesn't happen we disable interrupts at that time. We also use stack misuse during our draw routines, which will not go well, so we keep interrupts disabled. As the joystick connects to the AY port, There are also problems if interrupts occur during Joystick reading It's safest to disable interrupts for any code that may cause problems, the interrupts will wait if they occur while DI is in operation

ChibiTracks

To use ChibiTracks, we need to include the modules of the music player, We also need the platform specific "Chibisound Pro" sound driver.
We need to have a ChiBiTracks music file to play.
We have two options 'Allow Speed change' allows us to change the speed of our song. This is useful to keep the song playing the same speed on 50hz and 60hz screens. NOTE: Whether this will work effectively depends on if the speed was pre-multiplied on export (faster playback, but stops this function working) AllowRelocation allows the binary to be loaded at any memory address, not just the one 'compiled' into the binary at export time - while disabling this will save a little speed/memory it's recommended you keep this enabled!
We need to allocate up to 128 bytes of memory for ChibiSoundPro, and ChibiTracks player. We define pointers to the ChibiTracks variables within this ram. "ChibiOctaveAddr" is exclusive to the MSX - The WSX turbo mode plays at a different pitch, and we use this to tweak the octave table to compensate.
Before we play anything we need to init the ChibiSoundPro Driver. To start our song, we set SongBase to point to the music file we want to play, and call StartSong - we do this any time we want the music to change
All that's left is to execute the PLAY routine to update the playing music. ChibiTracks uses AF,BC,DE,HL and IX... it does not use IY or shadow registers.

In this mode an address is formed by taking the top byte from the R register, and the bottom byte from the interrupting device.
A 16 bit word is read from that address, and that address is called.
We can't effectively predict what the bottom byte will be, so we need to define a block of 257 bytes which all point to the same address.
The common solution is to fill memory addresses $8000-$8101 with the value $81. The effect of this is that all interrupts will call to $8181, and it's at that address  we put the code for (or jump to) our actual interrupt handler.
This is not very convenient, and IM 1 is far more useful. But on systems like the Spectrum, where low memory (Address &0038) is ROM, then this is the best solution for us.

Here we are reserving a block of 400 bytes at &8000 We'll use this to define the 257 byte address block for the IM2 handler, and the jump to the handler itself. Because we're at address &8000, the byte in register I will need to be &80
We use a LDIR to fill the 257 bytes with &8181 We load I with &80 - as our IM2 block starts at &80xx We as our IM2 block contains &8181, we put a jump at address &8181 to our actual interrupt handler. The area &8102-&817F is actually free for use (eg ram vars/stack)
Our interrupt handler updates the music. Chibitracks uses HL,BC,DE IX and AF only

ChibiTracks

To use ChibiTracks, we need to include the modules of the music player, We also need the platform specific "Chibisound Pro" sound driver.
We need to have a ChiBiTracks music file to play.
We have two options 'Allow Speed change' allows us to change the speed of our song. This is useful to keep the song playing the same speed on 50hz and 60hz screens. NOTE: Whether this will work effectively depends on if the speed was pre-multiplied on export (faster playback, but stops this function working) AllowRelocation allows the binary to be loaded at any memory address, not just the one 'compiled' into the binary at export time - while disabling this will save a little speed/memory it's recommended you keep this enabled! UseBeeper enables the beeper version (rather than the AY one for 128k) NoSilentPause disables the delay for silent ticks - our speed is controlled by the interrupt handler, so we don't need this SingleChannelBeeper will ignore all but channel 1 in the song, disabling this means the loudest of the 3 channels will be selected for the beeper to play
We need to allocate up to 128 bytes of memory for ChibiSoundPro, and ChibiTracks player. We define pointers to the ChibiTracks variables within this ram.
The spectrum beeper needs cpu time to make a sound - we set the speed with SetZX, we need to set short beeps (3) so that the interrupt handler doesn't take too much time and slow down our game. We clear the 'sound cache' used by the speccy ChibiSoundPro Driver - this is used to record what each channel should be playing, so the one that the beeper plays can be decided. Before we play anything we need to init the ChibiSoundPro Driver. To start our song, we set SongBase to point to the music file we want to play, and call StartSong - we do this any time we want the music to change
All that's left is to execute the PLAY routine to update the playing music. ChibiTracks uses AF,BC,DE,HL and IX... it does not use IY or shadow registers.

The gameboy processor isn't a Z80,but it's based on the 8080. It doesn't use IM1 for interrupts, but has a similar address that's called during vblank (&0040) - we'll update our music during that interrupt.

We need to put a jump to our interrupt handler on the VBLANK interrupt - this is at address &0040 We do this at the start of our ROM cartridge.
Our interrupt handler jump is in place, but we need to get the hardware to generate the interrupt , we do this with bit 0 of address &FFFF
Our interrupt handler updates the music. ChibiTracks uses all the registers, it also uses the 'fake' IX registers held in memory - we back these up as the rest of our program uses them too. We return with a RETI command

ChibiTracks

To use ChibiTracks, we need to include the modules of the music player. We also need the platform specific "Chibisound Pro" sound driver. ChibiTracks uses a variety of Z80 commands which do not exist on the GB, but we can simulate these with the "\SrcALL\CPU_Compatability.asm" macros
We need to have a ChiBiTracks music file to play.
We have two options 'Allow Speed change' allows us to change the speed of our song. This is useful to keep the song playing the same speed on 50hz and 60hz screens. NOTE: Whether this will work effectively depends on if the speed was pre-multiplied on export (faster playback, but stops this function working) AllowRelocation allows the binary to be loaded at any memory address, not just the one 'compiled' into the binary at export time - while disabling this will save a little speed/memory it's recommended you keep this enabled!
We need to allocate up to 128 bytes of memory for ChibiSoundPro, and ChibiTracks player. We define pointers to the ChibiTracks variables within this ram.
Before we play anything we need to init the ChibiSoundPro Driver. To start our song, we set SongBase to point to the music file we want to play, and call StartSong - we do this any time we want the music to change
All that's left is to execute the PLAY routine to update the playing music. ChibiTracks uses AF,BC,DE,HL and IX... On the gameboy, Z80 registers that do not exist are simulated with bytes in memory (r_ixl and r_ixh)