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Improved IOPAGE management

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This commit is contained in:
Jeff Parsons 2016-10-08 11:09:14 -07:00 • committed by Jeff Parsons
commit ae4fbeb489
7 changed files with 469 additions and 422 deletions
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25
modules/pdp11/lib/defines.js
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@ -79,16 +79,24 @@ var BYTEARRAYS = false;
var TYPEDARRAYS = (typeof ArrayBuffer !== 'undefined');
/**
* WORDBUS forces the Bus and Memory interfaces to assume even addresses when accessing words. Since PDPjs inherited
* its Bus component from PCx86, it originally supported both aligned and unaligned word accesses by default, but since
* the PDP-11 requires aligned (even) word addresses, we can turn off support for unaligned accesses and get some
* performance gains.
* MEMFAULT forces the Memory interfaces to signal a CPU fault when a word is accessed using an odd (unaligned) address.
*
* When WORDBUS is true, the Bus and Memory components simply ignore the low bit of word addresses, because it is the
* CPU, not the Bus, that's responsible for validating addresses and generating the appropriate traps.
* Since PDPjs inherited its Bus component from PCx86, it included support for both aligned and unaligned word accesses
* by default. However, the PDP-11 adds a wrinkle: when an odd address is used to access a memory word, a BUS_ERROR trap
* must be generated. Note that odd IOPAGE word accesses are fine; this only affects the Memory component.
*
* Don't worry that the source code looks MORE complicated rather than LESS with the additional WORDBUS checks, because
* the Closure Compiler eliminates those checks and throws away the (unreachable) code blocks that deal with unaligned
* When the MMU is enabled, these checks may also be performed at a higher level, eliminating the need for them at the
* physical memory level.
*/
var MEMFAULT = true;
/**
* WORDBUS turns off support for unaligned memory words. Whereas MEMFAULT necessarily slows down memory word accesses
* slightly, WORDBUS is able to speed them up slightly, by assuming that all word accesses (which didn't fault) must be
* aligned. This affects all word accesses, even IOPAGE accesses, because it also eliminates cross-block boundary checks.
*
* Don't worry that the source code looks MORE complicated rather than LESS with the additional MEMFAULT and WORDBUS checks,
* because the Closure Compiler eliminates those checks and throws away the (unreachable) code blocks that deal with unaligned
* accesses.
*/
var WORDBUS = true;
@ -109,6 +117,7 @@ var PDP11 = {
MAXDEBUG: MAXDEBUG, // shared
PRIVATE: PRIVATE, // shared
TYPEDARRAYS:TYPEDARRAYS,
MEMFAULT: MEMFAULT,
WORDBUS: WORDBUS,
SITEHOST: SITEHOST, // shared
XMLVERSION: XMLVERSION, // shared