Misc/abrash-black-book
Watch
1
0
Fork
You've already forked abrash-black-book
 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Normal quotes

Browse source
This commit is contained in:
James Gregory 2013-12-30 18:34:31 +11:00
commit 18011c595a
352 changed files with 6040 additions and 6040 deletions
Download patch file Download diff file Expand all files Collapse all files

14
47-06.md
View file

@ -10,15 +10,15 @@ suffices to make Mode X about as fast as mode 13H. That alone makes Mode
X an attractive mode, given its square pixels, page flipping, and
offscreen memory, but superior performance would nonetheless be a
pleasant addition to that list. Superior performance is indeed possible
in Mode X, although, oddly enough, it comes courtesy of the VGA’s
in Mode X, although, oddly enough, it comes courtesy of the VGA's
hardware, which was never designed to be used in 256-color modes.
All of the VGA’s hardware assist features are available in Mode X,
All of the VGA's hardware assist features are available in Mode X,
although some are not particularly useful. The VGA hardware feature
that’s truly the key to Mode X performance is the ability to process
four planes’ worth of data in parallel; this includes both the latches
that's truly the key to Mode X performance is the ability to process
four planes' worth of data in parallel; this includes both the latches
and the capability to fan data out to any or all planes. For rectangular
fills, we’ll just need to fan the data out to various planes, so I’ll
fills, we'll just need to fan the data out to various planes, so I'll
defer a discussion of other hardware features for now. (By the way, the
ALUs, bit mask, and most other VGA hardware features are also available
in mode 13H—but parallel data processing is not.)
@ -45,7 +45,7 @@ potentially speeding up operations like rectangle fills by four times.
And, as it turns out, four-plane parallelism works quite nicely indeed.
Listing 47.6 is yet another rectangle-fill routine, this time using the
Map Mask to set up to four pixels per **STOS.** The only trick to
Listing 47.6 is that any left or right edge that isn’t aligned to a
Listing 47.6 is that any left or right edge that isn't aligned to a
multiple-of-four pixel column (that is, a column at which one four-pixel
set ends and the next begins) must be clipped via the Map Mask register,
because not all pixels at the address containing the edge are modified.
@ -55,7 +55,7 @@ than Listing 47.5—and also about four times faster than the same
rectangle fill in mode 13H. Understanding the bitmap organization and
display hardware of Mode X does indeed pay.
Note that the return from Mode X’s parallelism is not always 4x; some
Note that the return from Mode X's parallelism is not always 4x; some
adapters lack the underlying memory bandwidth to write data that fast.
However, Mode X parallel access should always be faster than mode 13H
access; the only question on any given adapter is how *much* faster.