A disk made of memory, brought up by whoever owns it
THE MACHINE SUPPLIES BLOCKS AND SAYS WHAT A DRIVE IS. It says nothing about filesystems, which is what leaves room for a system that would rather have its own - and is why the volatile bit is a fact about the hardware rather than a promise about SBFS. 0x26 what the selected drive is: bit 0, contents do not survive 0x27, 0x28 how many blocks it has --ram-disk N a drive of N blocks with memory behind it A drive of memory selects, reads, writes and has a size like any other, and a program cannot tell the difference except by how fast it was. The one thing it cannot work out for itself is that the contents are volatile, because an empty disk and a volatile disk look identical from outside. THAT BIT IS THE DIFFERENCE BETWEEN A DRIVE A SYSTEM MAY FORMAT ON SIGHT AND ONE IT MUST NOT. CosmOS formats a volatile drive it cannot read, because there was never anything on it to lose, and leaves every other unreadable drive alone - an unformatted floppy is not an invitation, it is a blank floppy. Removing that check formats somebody's blank disk, which is checked rather than asserted: cosmosBlankDisk boots with one and requires it to be refused. So CosmOS grew a format. The size comes from the drive rather than from a superblock, since a superblock states a size too and that is no use on a disk which has not got one yet. Sixteen directory blocks, 128 names, chosen rather than worked out: a scratch disk runs out of names long before room, and this machine cannot divide. The RAM disk is no faster on this emulator by default, and that is honest rather than disappointing: the emulated disk has no seek time unless asked for one. With --disk-cycles 10000 the same copy is 7.94M cycles against 8.70M, the difference being every write. run.sh takes "ram:2048" where an image name goes, which needs no removing between runs because there is nothing to remove. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
This commit is contained in:
Anachronaut
co-authored by
Claude Opus 5
Claude Opus 5
parent
6b51d6391f
commit
04f1ffabd4
@@ -136,6 +136,138 @@ sbfsMountTooBig:
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ADD ; Q is not zero: not a disk this will mount.
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RET
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; ---- Making a disk into a filesystem ----
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;
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; The machine hands out blocks and says how many; what they mean is the system's business.
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; That is the whole reason this exists here rather than only in the host tool: a machine with
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; a drive made of memory comes up with a drive full of zeroes, and zeroes are not a
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; filesystem. Somebody has to write the first one, and it should be whoever is going to read
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; it - which is also what leaves room for a system that would rather have its own.
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;
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; Q is zero if it worked. Everything on the drive is lost, which is why nothing calls this
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; except on a drive the machine has said is volatile.
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sbfsFormat:
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; How big it is, which only the drive can say. A superblock would say too, and a disk with
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; no superblock is exactly the case this is for.
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INA 0x27
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SETD.1 SbfsScratch
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STA.1
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INA 0x28
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INCD.1
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STA.1
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; The buffer, cleared, because everything not written below has to be nought and the
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; controller's buffer holds whatever was last read.
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SETD.0 SbfsBuffer
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RSTB
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sbfsFormatClear:
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RSTA
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STA.0
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INCD.0
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DECB
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BNB sbfsFormatClear ; 256 of them: B wraps from nought to 255 and back to nought.
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; "SBFS", and the version. Two, because a disk made now has directories.
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SETD.0 SbfsMagic
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SETD.1 SbfsBuffer
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INIB 0d4
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sbfsFormatMagic:
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LDA.0
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STA.1
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INCD.0
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INCD.1
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DECB
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BNB sbfsFormatMagic
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INIA 0d2
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STA.1 ; Offset 4: the version.
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; Offset 6, how many blocks the disk has, as the drive reported it.
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SETD.1 SbfsBuffer
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DPUP.1 0d06
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SETD.0 SbfsScratch
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LDA.0
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STA.1
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INCD.0
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INCD.1
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LDA.0
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STA.1
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; Offset 8, where the directory starts: block one, straight after this one.
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SETD.1 SbfsBuffer
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DPUP.1 0d08
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RSTA
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STA.1
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INCD.1
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INIA 0d1
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STA.1
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; Offset 10, how many blocks of directory. SIXTEEN, WHICH IS 128 NAMES, and chosen rather
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; than worked out: a scratch disk runs out of names long before it runs out of room, and
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; this machine cannot divide, so a number that fits every size this is used for is worth
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; more than arithmetic to find a better one.
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SETD.1 SbfsBuffer
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DPUP.1 0d10
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RSTA
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STA.1
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INCD.1
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INIA 0d16
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STA.1
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; Block nought, written.
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SETD.0 SbfsBlock
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RSTA
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STA.0
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INCD.0
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STA.0
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SETD.1 SbfsBuffer
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CALL sbfsBufferIn
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CALL sbfsWriteBlock
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BNQ sbfsFormatFailed
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; And the directory cleared, so that no entry is in use. The buffer is already nought
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; everywhere the superblock did not reach, so it is cleared once more and written sixteen
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; times rather than built again each time.
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SETD.0 SbfsBuffer
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RSTB
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sbfsFormatBlank:
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RSTA
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STA.0
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INCD.0
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DECB
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BNB sbfsFormatBlank
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INIA 0d16
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SETD.1 SbfsCount
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STA.1
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sbfsFormatDirectory:
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SETD.0 SbfsBlock
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INCD.0
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LDA.0
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INCA
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STA.0 ; Blocks one to sixteen. A directory never crosses 255 here.
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SETD.1 SbfsBuffer
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CALL sbfsBufferIn
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CALL sbfsWriteBlock
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BNQ sbfsFormatFailed
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SETD.1 SbfsCount
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LDA.1
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DECA
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STA.1
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BNA sbfsFormatDirectory
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RSTA
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RSTB
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CCF
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ADD
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RET
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sbfsFormatFailed:
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RSTA
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INIB 0d1
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CCF
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ADD
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RET
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; ---- Every drive the machine has ----
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;
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; Asked for rather than assumed: the controller says how many are plugged in, and each is
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@@ -192,7 +324,29 @@ sbfsMountEach:
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STA.1
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CALL sbfsMount
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BNQ sbfsMountNext ; Nothing readable in that drive, and its slot stays empty.
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BRQ sbfsMountGot
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; ---- Nothing readable, and whether that is an invitation ----
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;
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; A drive the machine calls VOLATILE loses everything when the machine stops, so a volatile
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; drive with no filesystem on it never had one to lose and bringing it up is the system's
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; job. Anything else is somebody's disk: an unformatted floppy is not an invitation, it is
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; a blank floppy, and a system that formatted it on sight would be a system you could not
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; safely put a disk into.
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;
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; THE MACHINE SAYS WHAT THE DRIVE IS AND NOTHING ABOUT FILESYSTEMS. A system that would
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; rather have its own reads the same bit and writes whatever it likes.
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INA 0x26
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INIB 0x01 ; VOLATILE
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AND
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BRQ sbfsMountNext ; Not ours to touch.
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CALL sbfsFormat
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BNQ sbfsMountNext
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CALL sbfsMount
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BNQ sbfsMountNext
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sbfsMountGot:
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; Mounted: remember which, and put the live record where it belongs.
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SETD.1 SbfsDriveAt
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