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Mistakes in books: Sedoric à Nu

Posted: Fri Dec 04, 2015 10:52 pm
by Symoon
Page 207, address D503, André wonders if there's not a bug as a JSR D7BD seems to be repeated very closely.
It is also listed as an uncorrected bug page 571.

This is not a bug.
Actually, the code here is trying to validate the drive letter asked by the user. But there are two ways to ask for a drive:
1- entering "A-" (or B- or C- or D- ) will set the default drive to the chosen letter. Any file load attempt will be made from this default drive
2- loading a file specifying the drive where it's stored, therefore bypassing the default drive, for instance: LOAD"B-ZAKMCKRAK" will load the file ZAKMCKRAK on the drive B, whatever the default drive is (and providing Chema has ported the game ;))

So the two JSR D7BD are there for these two ways of asking for a drive: one will just be used to load a file, the other will set the default drive. They are two different entries, each one requiring (more or less, but that's another story) the JSR D7BD.

Re: Mistakes in books: Sedoric à Nu

Posted: Fri Dec 04, 2015 11:12 pm
by Symoon
Page 497, is written:
octet 0F attribut de protection (b6=1, PROT si b7=1, UNPROT si b7=0)
(#40 = 0100 0000 pour UNPROT et #C0 = 1100 0000 pour PROT). b0 à b5 = HH du nombre de secteurs = rarement utilisés, sauf pour les très gros fichiers mergés.
In other words, the book explains that in a file catalog entry, bits 0 to 5 of a dedicated byte are the most significant bits of a file size (in occupied sectors). So displaying this size would use 8 bits + bits 0 to 5 = up to 14 bits.

This seems unlikely, it should rather be bits 0 to 3 (so 12 bits), leading to a maximum size of 4096 sectors, which is 1MB. Don't think any disk would hold such a big file!
Also, page 278, address #E331, is an AND#0F (mask 00001111), proof that only 4 bits are used.
This has also been tested by setting the 5th bit to 1: DIR doesn't show any file size change, but altering the 3rd bit instead affects the displayed size indeed.

So actually, bit 4 and bit 5 were unused. Bit 5 is now dedicated to flag a directory (in the Sedoric directories demo).
(This mistake was explained in the CEO-Magazine looong ago)

Re: Mistakes in books: Sedoric à Nu

Posted: Sun Dec 06, 2015 11:39 pm
by Godzil
Thanks Symoon for that errata :)