Reading CDDA sound levels: Difference between revisions
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(Created page with "Registers '''REG_CDDALEFTL''' ($FF0188) and '''REG_CDDARIGHTL''' ($FF01AA) hold the values of the currently streamed CD audio data, in a reversed 16bit 2's complement format suit…") |
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The CD2 [[BIOSes|BIOS]] uses the following code to reverse the bits: | The CD2 [[BIOSes|BIOS]] uses the following code to reverse the bits: | ||
<pre> | <pre> | ||
;D1:Input | ;D1:Input, D0:Output | ||
reverse16bits: | reverse16bits: | ||
moveq #16-1,d7 | moveq #16-1,d7 | ||
| Line 16: | Line 15: | ||
</pre> | </pre> | ||
The CD2 BIOS reads both registers multiple times during each frame (every 16 raster lines, by using the [[68k interrupts|raster interrupt]]) to get an average value. The displayed vu-meters use a double buffer to avoid getting updated with the average of only the first few register reads (those that were made before the vu-meters were actually drawn to the screen). | |||
==Demo== | |||
[[File:screencap_cddaviz.png|right]] | |||
Uses: | |||
*Raster line interrupts | |||
*[[Sprites]] (shrink and displacement) | |||
*[[Fix layer|Fix]] (displays hex value) | |||
*[[Palettes]] | |||
[[http://furrtek.free.fr/noclass/neogeo/demo_vumeter1.zip Source and ISO image]] | |||
[[http://www.youtube.com/watch?v=JP5VAypJIYk Youtube video | [[http://www.youtube.com/watch?v=JP5VAypJIYk Youtube video]] | ||
[[Category:Code]] | [[Category:Code]] | ||
[[Category:HowTo]] | |||
Revision as of 22:49, 20 April 2011
Registers REG_CDDALEFTL ($FF0188) and REG_CDDARIGHTL ($FF01AA) hold the values of the currently streamed CD audio data, in a reversed 16bit 2's complement format suited for the LC78815 DAC (Sample rate =~ 100kHz ?).
The CD2 BIOS uses the following code to reverse the bits:
;D1:Input, D0:Output
reverse16bits:
moveq #16-1,d7
moveq #0,d0
rev:
lsr #1,d1
bcc zerobit
bset d7,d0
zerobit:
dbf d7,rev
The CD2 BIOS reads both registers multiple times during each frame (every 16 raster lines, by using the raster interrupt) to get an average value. The displayed vu-meters use a double buffer to avoid getting updated with the average of only the first few register reads (those that were made before the vu-meters were actually drawn to the screen).
Demo
Uses: