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Improved geometry calculation for all disk images, not just those listed in DiskAPI.js

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This commit is contained in:
Jeff Parsons 2017-06-01 20:59:41 -07:00 • committed by Jeff Parsons
commit 5441c6346b
5 changed files with 76 additions and 61 deletions
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58
modules/diskdump/lib/diskdump.js
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@ -527,6 +527,22 @@ DiskDump.aDefaultBPBs = [
0x02, 0x00, // 0x1A: number of heads (2)
0x00, 0x00, 0x00, 0x00 // 0x1C: number of hidden sectors (always 0 for non-partitioned media)
],
/*
* Here's some useful background information on a 10Mb PC XT fixed disk, partitioned with a single DOS partition.
*
* The BPB for a 10Mb "type 3" PC XT drive specifies 0x5103 or 20739 for TOTAL_SECS, which is the partition
* size in sectors (10,618,368 bytes), whereas the total disk size is 20808 sectors (10,653,696 bytes). The partition
* is 69 sectors smaller than the disk because the first sector is reserved for the MBR and 68 sectors (the entire last
* cylinder) are reserved for diagnostics, head parking, etc. This cylinder usage is confirmed by FDISK, which reports
* that 305 cylinders (not 306) are assigned to the DOS partition.
*
* That 69-sector overhead is NOT the overhead incurred by the FAT file system, which is the boot sector (1), FAT
* sectors (16), and root directory sectors (32), for a total of 49 sectors, leaving 20739 - 49 or 20690 sectors.
* However, free space is measured in clusters, not sectors, and the partition uses 8 sectors/cluster, leaving room
* for 2586.25 clusters. Since a fractional cluster is not allowed, another 2 sectors are lost to FAT overhead,
* for a total of 51 sectors. So actual free space is (20739 - 51) * 512, or 10,592,256 bytes -- which is exactly
* what is reported as the available space on a freshly formatted PC XT 10Mb fixed disk.
*/
[ // define BPB for 10Mb hard drive
0xEB, 0xFE, 0x90, // 0x00: JMP instruction, following by 8-byte OEM signature
0x50, 0x43, 0x4A, 0x53, 0x2E, 0x4F, 0x52, 0x47, // PCJS_OEM
@ -2496,7 +2512,6 @@ DiskDump.prototype.convertToJSON = function()
var json = null;
var fOptimize = true; // if true, leave out any properties that are defaults
try {
var fMBR = false;
var nHeads = 0;
var nCylinders = 0;
var nSectorsPerTrack = 0;
@ -2505,7 +2520,7 @@ DiskDump.prototype.convertToJSON = function()
var cbSector = 512; // default sector size
var bMediaType = 0;
var offBootSector = 0;
var cbDiskData = this.bufDisk.length;
var cbDiskData = this.bufDisk.length, cbPartition = cbDiskData;
if (cbDiskData >= 3000000) { // arbitrary threshold between diskette image sizes and hard drive image sizes
var wSig = this.bufDisk.readUInt16LE(DiskAPI.BOOT.SIG_OFFSET);
@ -2517,8 +2532,7 @@ DiskDump.prototype.convertToJSON = function()
for (var offEntry = 0x1BE; offEntry <= 0x1EE; offEntry += 0x10) {
if (this.bufDisk.readUInt8(offEntry) >= 0x80) {
offBootSector = this.bufDisk.readUInt32LE(offEntry + 0x08) * cbSector;
cbDiskData = this.bufDisk.readUInt32LE(offEntry + 0x0C) * cbSector;
fMBR = true;
cbPartition = this.bufDisk.readUInt32LE(offEntry + 0x0C) * cbSector;
break;
}
}
@ -2548,7 +2562,7 @@ DiskDump.prototype.convertToJSON = function()
* image whose logical format doesn't agree with its physical structure.
*/
var fXDFOutput = false;
var diskFormat = DiskAPI.DISK_FORMATS[cbDiskData];
var diskFormat = DiskAPI.GEOMETRIES[cbDiskData];
if (diskFormat) {
nCylinders = diskFormat[0];
nHeads = diskFormat[1];
@ -2579,11 +2593,7 @@ DiskDump.prototype.convertToJSON = function()
var nSectorsTotalBPB = this.bufDisk.readUInt16LE(offBootSector + DiskAPI.BPB.TOTAL_SECS);
var nSectorsPerCylinderBPB = nSectorsPerTrackBPB * nHeadsBPB;
var nCylindersBPB = Math.floor(nSectorsTotalBPB / nSectorsPerCylinderBPB);
/*
* TODO: Detect newer BPBs (ie, where the HIDDEN_SECS and LARGE_SECS fields are valid),
* so that we can determine the true geometry of the disk, instead of having to rely on our
* DISK_FORMATS table.
*/
if (diskFormat) {
if (nCylinders != nCylindersBPB) {
DiskDump.logWarning("BPB cylinders (" + nCylindersBPB + ") do not match actual cylinders (" + nCylinders + ")");
@ -2599,9 +2609,13 @@ DiskDump.prototype.convertToJSON = function()
}
}
else {
nCylinders = nCylindersBPB;
nHeads = nHeadsBPB;
nSectorsPerTrack = nSectorsPerTrackBPB;
nCylinders = cbDiskData / (nHeads * nSectorsPerTrack * cbSector);
if (nCylinders != (nCylinders|0)) {
DiskDump.logWarning("total cylinders (" + nCylinders + ") not a multiple of heads (" + nHeads + ") and sectors/track (" + nSectorsPerTrack + ")");
nCylinders |= 0;
}
bMediaType = bMediaTypeBPB;
}
@ -2645,8 +2659,11 @@ DiskDump.prototype.convertToJSON = function()
if (bMediaType) {
for (i = 0; i < DiskDump.aDefaultBPBs.length; i++) {
if (DiskDump.aDefaultBPBs[i][DiskAPI.BPB.MEDIA_TYPE] == bMediaType) {
iBPB = i;
break;
var cbDiskBPB = (DiskDump.aDefaultBPBs[i][DiskAPI.BPB.TOTAL_SECS] + (DiskDump.aDefaultBPBs[i][DiskAPI.BPB.TOTAL_SECS + 1] * 0x100)) * cbSector;
if (cbDiskBPB == cbDiskData) {
iBPB = i;
break;
}
}
}
}
@ -2696,15 +2713,14 @@ DiskDump.prototype.convertToJSON = function()
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 (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 pre-2.0 disks (and non-DOS disks, obviously).
*/
this.bufDisk.write(DiskDump.PCJS_OEM, DiskAPI.BOOT.OEM_STRING + offBootSector, DiskDump.PCJS_OEM.length);
}
if (!nHeads) {
/*
* Next, check for a DSK header (an old private format I used to use, which begins with either