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Updated PIT nomenclature, added more DeskPro 386 ROM notes

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This commit is contained in:
Jeff Parsons 2015-04-15 10:59:57 -07:00 • committed by jeffpar
commit 9b1de72137
5 changed files with 594 additions and 548 deletions
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14
modules/pcjs/lib/memory.js
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@ -498,6 +498,18 @@ Memory.prototype = {
/**
* readNone(off)
*
* Previously, this always returned 0x00, but the initial memory probe by the Compaq DeskPro 386 ROM BIOS
* writes 0x0000 to the first word of every 64Kb block in the nearly 16Mb address space it supports, and so
* it would initially think that LOTS of RAM existed, only to be disappointed later when it performed a more
* exhaustive memory test, and generating error messages in the process.
*
* TODO: Determine if we should have separate readByteNone(), readShortNone() and readLongNone() functions
* to return 0xff, 0xffff and 0xffffffff|0, respectively. This seems sufficient, as it seems unlikely
* that a system would require nonexistent memory locations to have all bits set.
*
* Also, I'm reluctant to address that potential issue by simply returning -1, because to date, the Memory
* component has always provided return values that are properly masked, and some callers may depend on that.
*
* @this {Memory}
* @param {number} off
* @return {number}
@ -506,7 +518,7 @@ Memory.prototype = {
if (DEBUGGER && this.dbg.messageEnabled(Messages.MEM) /* && !off */) {
this.dbg.message("attempt to read invalid block %" + str.toHex(this.addr) + " from " + this.dbg.hexOffset(this.cpu.getIP(), this.cpu.getCS()));
}
return 0;
return 0xff;
},
/**
* writeNone(off, v)