Thiago, this code might help you, first to register into HKEY_I hook:
Wow, do you know me? Sorry, I can't remember you. :-( At least not by this nickname.
ramad1 equ 0xF342 di ld (intr_handler+1), hl ; Replace in intr_handler the address ; save hookint ld hl, #hookint ld de, #backup_hookint ld bc, #5 ldir ld a, #0xF7 ; RST_30 (interslot call both dos and bios) ld (hookint), a ld a, (ramad1) ld (hookint+1), a ld hl, #intr_handler ld (hookint+2), hl ld a, #0xc9 ld (hookint+4), a ei backup_hookint: .ds 5
This might help you, even though it is intended to use interslot call, you can replace it by call to a P3 address if your routine is there, instead of using it, then you won't need ramad1 (slot of ram in page 1, which is the program ram in case of DOS, you might want to change to ramad2 depending on your needs, i.e.: if it is something running in BASIC, it will be running on page 2). It is important to backup the original hook 5 bytes so you can call it after doing your interrupt, you need to chain in this way, otherwise, it won't be nice to any other piece of BIOS/ROM/DRIVER that is hooking there and will no longer get called on interrupts... By the way, this code assumes HL has the address of your HKEY_I routine...
is this some kind of hook installer that don't trashes already installed hooks? Neat!
At the end of your program, you can try to get yourself out of the hook by doing this, but only if you are running a program, if you are doing resident stuff (i.e.: allocating a system mapper segment that gets called) this might not work as there is a good chance you are no longer the last to hook:
di ld hl, #backup_hookint ld de, #hookint ld bc, #5 ldir ei ret
intr_handler: call dummy_handler ; This will be replaced by user routine address dummy_handler: jp backup_hookint ; And continue processing interrupt hooks ret
And this is your code executing whenever an interrupt is called... As you can see, this is as generic as can be (this was my proposition, which I had help from DarkSchneider, for functions to register a SDCC function to HKEY_I interrupt). In your case, you might just erase the first LD after DI in the install routine, and below intr_handler put all your interrupt code, just make sure it ends with jp backup_hookint to execute the previous hook and has a ret below, so you will return after the backup hook returns...
This works quite well with SDCC and should work on your code as well. 
Well... this code is meant to be "resident stuff" (it will grow to animate tiles and palettes, it already has a very simple V9990 splitscreen code) so it should RETurn normally.
Thiago, this code might help you, first to register into HKEY_I hook:
Wow, do you know me? Sorry, I can't remember you. :-( At least not by this nickname.
Hi, yeah, Facebook MSX Group, I'm Oduvaldo, the guy behind MSX Telnet and SM-X WiFi 
Well... this code is meant to be "resident stuff" (it will grow to animate tiles and palettes, it already has a very simple V9990 splitscreen code) so it should RETurn normally.
By resident, I mean a code that is running besides another application, i.e.: a ROM DISK, an UNAPI ROM or driver... Those codes only execute to install it's hooks (both hooking to hooks or creating their own hooks, i.e.: UNAPI hook, EXTBIO, etc) and initialize everything, then that code will be running along with other applications, being either invoked by a hook, interrupt, etc... In that case, as you install your stuff and system continues with other applications, someone else might hook after you and if you simply remove your hook, you kill the hook chain after you, for resident applications, if you wan't to disable your hooking, instead of removing yourself from the hook, you just make your hook code to jump directly to your hook backup, so it doesn't break the hook chain...
If your code will not, ever, exit and return control, or if when it exits it is done and no part of it is kept running, it is not resident (i.e.: games, most dos applications, etc). In that case, just remove your hook entry before exiting, so the system won't crash once your program is unloaded or overwritten in the memory
(...)By resident, I mean a code that is running besides another application, i.e.: a ROM DISK, an UNAPI ROM or driver... Those codes only execute to install it's hooks (both hooking to hooks or creating their own hooks, i.e.: UNAPI hook, EXTBIO, etc) and initialize everything, then that code will be running along with other applications, being either invoked by a hook, interrupt, etc... In that case, as you install your stuff and system continues with other applications, someone else might hook after you and if you simply remove your hook, you kill the hook chain after you, for resident applications, if you wan't to disable your hooking, instead of removing yourself from the hook, you just make your hook code to jump directly to your hook backup, so it doesn't break the hook chain...
In my MS-DOS days, this type of program were called "TSR" (Terminate and Stay Resident). Yes, that's exactly what I am doing here.
If your code will not, ever, exit and return control, or if when it exits it is done and no part of it is kept running, it is not resident (i.e.: games, most dos applications, etc). In that case, just remove your hook entry before exiting, so the system won't crash once your program is unloaded or overwritten in the memory
It may happen in the future
