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#letscode

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Hm, I think Turbo C 2.01 has a very tricky, and VERY ancient bug. The intr() function from <dos.h> header SHOULD be able to pass ES:BP pointers to interrupts. However I think it doesn't. Using this gives garbage (or probably: the stack pointer) to the interrupt vector instead. I wonder if this could be patched...? How hard can it be to disassemble the .lib files?
#retrocomputing #turboc #letscode

New video:
Let's Code MS DOS 0x28: Expanded Memory EMS

The original IBM PC and MS DOS could — for the most part — only access 640KB of memory. The LIM EMS standard was at first a standard for RAM expansion cards to overcome this limit. Today we learn how to utilize EMS memory to play back an animation that is too large for conventional memory.

youtu.be/QS060vSzWLY

The Yamaha #opl2 is documented to have an ADSR curve where the key off triggers the release phase, as shown in the picture. However my tests using DOSBox show that the key off doesn't matter at all. It seems release is triggered as soon as decay phase is done. Is there a trick or another register that controls this behavior?
#letscode #retrocomputing

New video: Let's Code MS DOS 0x26: AdLib Drum Machine

Programming the OPL2 FM chip on the original AdLib card can be a bit tedious. Join me in this episode to learn how to program the drums on the AdLib card to create a simple sequencer or drum machine. In the future we will also look at the melodic instruments, but for now we try to create some nice percussion!

youtu.be/kP2B9a7Btpk

Let's Code MS DOS 0x24: Low Level Keyboard Programming

Getting input from the keyboard can be as easy as calling the getch() function. But for games we need a better solution. For games on MS DOS machines you need quick, unbuffered input. To simply get the state of keypresses we need to talk to the keyboard controller directly. Let’s have a look at how that’s done!

youtu.be/njeViEGaP-8

Let's Code MS DOS 0x23: 2nd Reality Lens Effect

In 1993 the Future Crew released the seminal demo “Second Reality”. Last episode we re-implemented the tunnel effect, this time we try to understand and replicate the lens effect. A bouncing, tinted glass ball that distorts the background image. Thirty years back it was pretty jaw dropping, and even today we can learn something!

youtu.be/7Lf4Z5YYbtU