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Added BPB to pre-2.0 DOS disks, for consistency and mounting support

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This commit is contained in:
Jeff Parsons 2017-06-01 09:15:39 -07:00 • committed by Jeff Parsons
commit b42c858c44
10 changed files with 58 additions and 32 deletions
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61
modules/diskdump/lib/diskdump.js
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@ -413,12 +413,6 @@ DiskDump.PCJS_OEM = "PCJS.ORG";
/**
* The BPBs that buildImage() currently supports; these BPBs should be in order of smallest to largest capacity,
* to help ensure we don't select a disk format larger than necessary.
*
* TODO: For now, the code that chooses a default BPB is starting with #3 instead of #0, because Windows 95 (at least
* when running under VMware) fails to read the contents of such disks correctly. Whether that's my fault or Windows 95's
* fault is still TBD (although it's probably mine -- perhaps 160Kb diskettes aren't supposed to have BPBs?) The simple
* work-around is to avoid creating 160Kb diskette images (and, to play it safe, I skip 180Kb and 320Kb as well, since
* 360Kb was the most commonly used format after DOS 2.0 introduced it).
*/
DiskDump.aDefaultBPBs = [
[ // define BPB for 160Kb diskette
@ -1460,7 +1454,7 @@ DiskDump.prototype.validateTime = function(dateTime)
/*
* The year in a DOS modification date occupies 7 bits and is interpreted as a non-negative value (0-127)
* that is added to the base year of 1980, so the range of valid years is 1980-2107. However, it's worth
* nothing that in PC-DOS 2.0, I observed a date with the largest possible year value (127) displayed as
* noting that in PC-DOS 2.0, I observed a date with the largest possible year value (127) displayed as
* "12-31-:7" (an ASCII ':' is the next highest character after '0'). While that DOES distinguish the year
* 2007 from the year 2107, we probably shouldn't allow any year > 2099, to eliminate confusion.
*
@ -1496,7 +1490,7 @@ DiskDump.prototype.buildData = function(cb, abInit)
{
var ab = new Array(cb);
for (var i = 0; i < cb; i++) {
ab[i] = (abInit && i < abInit.length? abInit[i] : 0);
ab[i] = abInit && abInit[i] || 0;
}
return ab;
};
@ -2329,14 +2323,23 @@ DiskDump.prototype.buildImageFromFiles = function(aFiles, done)
var cRootEntries, cRootSectors, cTotalSectors, cSectorsPerTrack, cHeads, cDataSectors, cbAvail;
/*
* Find or build a BPB with enough capacity, and at the same time, calculate all
* the other values we'll need, including total number of data sectors (cDataSectors).
* Find or build a BPB with enough capacity, and at the same time, calculate all the other values we'll need,
* including total number of data sectors (cDataSectors).
*
* TODO: For now, the code that chooses a default BPB is starting with #3 instead of #0, because Windows 95
* (at least when running under VMware) fails to read the contents of such disks correctly. Whether that's my
* fault or Windows 95's fault is still TBD (although it's probably mine -- perhaps 160Kb diskettes aren't
* supposed to have BPBs?) The simple work-around is to avoid creating 160Kb diskette images (and, to play it
* safe, I skip 180Kb and 320Kb as well, since 360Kb was the most commonly used format after DOS 2.0 introduced it).
*/
for (var iBPB = 3; iBPB < DiskDump.aDefaultBPBs.length; iBPB++) {
/*
* Use slice() to copy the default BPB, as a precaution (to avoid any changes to the default).
*/
abBoot = DiskDump.aDefaultBPBs[iBPB].slice();
/*
* If this BPB is for a hard drive but a disk size was not specified, skip it.
*/
abBoot = DiskDump.aDefaultBPBs[iBPB];
if ((abBoot[0x15] == 0xF8) != (this.kbTarget >= 10000)) continue;
cbSector = abBoot[0x0B] | (abBoot[0x0C] << 8);
cSectorsPerCluster = abBoot[0x0D];
@ -2384,7 +2387,7 @@ DiskDump.prototype.buildImageFromFiles = function(aFiles, done)
this.bufDisk.fill(0);
/*
* Output a Master Boot Record (MBR), if a hard drive image was requested
* Output a Master Boot Record (MBR), if a hard drive image was requested.
*/
if (this.kbTarget >= 10000) {
abSector = this.buildMBR(cHeads, cSectorsPerTrack, cbSector, cTotalSectors);
@ -2392,10 +2395,10 @@ DiskDump.prototype.buildImageFromFiles = function(aFiles, done)
}
/*
* Output a boot sector
*
* NOTE: I don't put a [0x55,0xAA] signature at the end, since it's not actually bootable.
* Output a boot sector.
*/
abBoot[DiskAPI.BOOT.SIG_OFFSET] = 0x55;
abBoot[DiskAPI.BOOT.SIG_OFFSET + 1] = 0xAA;
abSector = this.buildData(cbSector, abBoot);
offDisk += this.copyData(offDisk, abSector);
@ -2497,8 +2500,8 @@ DiskDump.prototype.convertToJSON = function()
var cbDiskData = this.bufDisk.length;
if (cbDiskData >= 3000000) { // arbitrary threshold between diskette image sizes and hard drive image sizes
var wSig = this.bufDisk.readUInt16LE(0x1FE);
if (wSig == 0xAA55) {
var wSig = this.bufDisk.readUInt16LE(DiskAPI.BOOT.SIG_OFFSET);
if (wSig == DiskAPI.BOOT.SIGNATURE) {
/*
* In this case, the first sector should be an MBR; find the active partition entry,
* then read the LBA of the first partition sector to calculate the boot sector offset.
@ -2642,13 +2645,22 @@ DiskDump.prototype.convertToJSON = function()
var bActual = this.bufDisk.readUInt8(offBootSector + i);
if (bDefault != bActual) {
DiskDump.logWarning("BPB byte " + str.toHexByte(i) + " default (" + str.toHexByte(bDefault) + ") does not match actual byte: " + str.toHexByte(bActual));
fBPBExists = false;
}
}
}
else if (bByte0 == X86.OPCODE.JMPS && bByte1 >= 0x22) {
/*
* I'm going to stick my neck out here and slam a BPB into this disk image, since it doesn't appear
* to have one, which should make it more "mountable" on modern operating systems.
* to have one, which should make it more "mountable" on modern operating systems. PC-DOS 1.x (and
* the recently unearthed PC-DOS 0.x) are OK with this, because they don't put anything important in
* the BPB byte range (0x00B-0x023), just a 9-byte date string (eg, " 7-May-81") at 0x008-0x010,
* followed by zero bytes at 0x011-0x030.
*
* They DO, however, store important constants in the range later used as the 8-byte OEM string at
* 0x003-0x00A. For example, the word at 0x006 contains the starting segment for where to load
* IBMBIO.COM and IBMDOS.COM. Those same early boot sectors are also missing the traditional 0xAA55
* signature at the end of the boot sector.
*/
for (i = DiskAPI.BPB.SECTOR_BYTES; i < DiskAPI.BPB.LARGE_SECS+4; i++) {
this.bufDisk.writeUInt8(DiskDump.aDefaultBPBs[iBPB][i] || 0, offBootSector + i);
@ -2667,6 +2679,14 @@ DiskDump.prototype.convertToJSON = function()
else {
DiskDump.logWarning("unrecognized boot sector: " + str.toHexByte(bByte0) + "," + str.toHexByte(bByte1));
}
if (fBPBExists) {
/*
* Overwrite the OEM string with our own, so that people know how the image originated. We do this
* only for disks with pre-existing BPBs; it's not safe for older disks (and non-DOS disks, obviously).
*/
this.bufDisk.write(DiskDump.PCJS_OEM, DiskAPI.BOOT.OEM_STRING, DiskDump.PCJS_OEM.length);
}
}
if (!nHeads) {
@ -3204,9 +3224,10 @@ DiskDump.prototype.convertToIMG = function()
*/
var bByte0 = buf.readUInt8(DiskAPI.BOOT.JMP_OPCODE);
var cbSectorBPB = buf.readUInt16LE(DiskAPI.BPB.SECTOR_BYTES);
if ((bByte0 == X86.OPCODE.JMP || bByte0 == X86.OPCODE.JMPS) && cbSectorBPB == 512) {
var wSig = buf.readUInt16LE(DiskAPI.BOOT.SIG_OFFSET);
if ((bByte0 == X86.OPCODE.JMP || bByte0 == X86.OPCODE.JMPS) && cbSectorBPB == 512 && wSig == DiskAPI.BOOT.SIGNATURE) {
/*
* Overwrite the OEM string with our own, so that people know how the image originated
* Overwrite the OEM string with our own, so that people know how the image originated.
*/
buf.write(DiskDump.PCJS_OEM, DiskAPI.BOOT.OEM_STRING, DiskDump.PCJS_OEM.length);
}