Re: 3 Key Presses---(I know it wasn't directed to me.. but..)


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Posted by Andy Warne on 20, 2001 at 2:53 PM:

In Reply to: 3 Key Presses---(I know it wasn't directed to me.. but..) posted by Intensify on 19, 2001 at 9:25 AM:

Everything "Intensify" said is correct. The key codes each take 1.5 millisecs to send, in order, to the PC. One frame is about 40 milliseconds so assuming 25 FPS so in theory the encoder could do it provided it is a type which handles each key individually with respect to de-bounce etc. The problem is not with the encoder but with the emulator and the keyboard engine. This may introduce a delay which exceeds one frame. So there may still be a problem with this.
Regarding USB, a USB keyboard sends a "report" of all keys pressed so it is sending all the codes at the same time. But this advantage is more than cancelled out by the USB drivers on the PC which actually (believe it or not!) reformat the USB data byte into PS/2 style key codes and send it to the ordinary keyboard driver.
It would probably be quite easy to write a program around the Allegro keyboard engine to test this functionality. Anyone....?

: Bugfinder:

: This is definitely a limitation of the keyboard (ps2 port). It is, technically, IMPOSSIBLE to push 3 buttons at **EXACTLY** the same time. It may be close (like milliseconds), but the keyboard encoder scans at a fixed rate picking up keypresses and sending them IN ORDER to the computer via the PS/2 Port.

: On an arcade machine, however, the buttons are, more or less, wired DIRECTLY to the pcb (through some kind of connector). This allows you to literally register 3 button presses at EXACTLY the same time.

: However, the chances that you actually pushed all 3 buttons in the arcade at *EXACTLY* the same time are slim to none, there had to be a delay, albeit VERY SMALL, between the presses. However, if a ps/2 keyboards scan rate is too slow, it would show that delay as much larger.

: Now i've heard that USB Keyboards have a faster scan rate than ps/2 keyboard but am unsure if this is a limitation of the ps/2 port or just the keyboardds themselves.

: I have an e-mail into Hagstrom Electronics (keyboard encoders) and am inquiring about the whole situation, and will let you know as soon as I get a response what they said.

: --Intensify




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