Indeed, IMHO people is overreacting a bit about that. IIRC someone gave here some more details about those PSG bits and the strange behaviour behind them, I don't remember the thread; but he told us that if they're badly initialized, they make the joysticks stop working...and not always. I doesn't care anymore, luckily it's very easy to avoid, just a matter of be careful...

I say: Myth 60% / Fact 40%

 

There are MSX2 machines that hang very hard and need a power cycle to work again (reset doesn't work) when these bits are badly written. Quibus confirmed this with his Sony HB-G900P. That means there is a high possibility a lot of MSX1 machines will have the same reaction, or possibly even one involving smoke.

Just think about it: You're making and input port out of an output (or an output out of an input) and then put 5V on it... What do you think will happen Try driving on the wrong side of the road with your car to find out!

But, regardless of any physical damage:
1. It makes joysticks not work for a lot of machines. (so it's a BUG)
2. It's against the MSX standard.
3. It's so easy to fix...

If you feel sad about programmers getting bad comments, maybe you also feel sad when they don't know how to access the disk properly and format your harddisk by accident? It's the same thing...

Denying this 'myth' is the same as saying it's ok to play with a loaded gun.

after a brief talk in the cool irc channel

set the ports the correct way, or the joysticks don't work, but it probably isn't harmful "generally"

if your msx is setup the way the schematic is in the tech manual, then "no joystick"

if however some are different, as it seems to be from the stuff above with some machines crashing hard, then not setting up r7 in the correct way is a programmer fault, it's meant to be one way only, or else it's wrong, I'd call the joyports being disabled wrong.

maybe someone could put up a list of the machines that completely malfunction and the ones that just have no joyport functionality.

having said all this of course, a machine that stops dead when r7 isn't the way it's meant to be is maybe a borked by design machine

either way, just set up r7 the happy way and it'll work for everyone

I'm just going off the pictures in the sony msxtech.pdf it shows an actual ay chip connected to actual 74 series chips, msx engine machines may have subtle variations that cause this to vary from inconvenience to badness.

if you got both ports as input it'l mean that the then "inputs" on port b would be connected to inputs on the 74 series chips that are directly connected, been given the impression that 's not a harmful situation, but it does mess with my head as being abuse of logic

other way around feels like bad karma to me but I'm probably just being scared

the machines that stop dead on r7 abuse, all msx engine machines? I take it there's different versions of msx engine maybe there's subtle optimisations and differences that give rise to badness

so I guess it's setup r7 the one true way™ and that's that

that makes a lot of sense actually, as you aren't supposed to alter them from what they are meant to be, trying to do anything to them would be meaningless in this case

I guess it's just one of those subtle design things that requires doing things in a particular way due to the design

er, if that makes any sense