HP-41 and Hepax Filesystem

[Ángel Martin]

(02-07-2020 11:35 AM)pablo2000 Wrote:  Many thanks to both of you - some useful stuff in there, although I was already aware of much, but by no means all, of it.

The key information I'm after is this bit ->

(02-06-2020 04:07 AM)Sylvain Cote Wrote:  HEPAX file header uses 10 bytes
HEPAX data record use 6 bytes

I can reverse engineer it if I have to, but it strikes me as odd that a module as revered, almost a cult following, as Hepax has so little publicly available information. And believe me, I've trawled all the old publications, forums and corners of the internet! It may help if I share a little of the purpose for it. Apologies if this is a little long.

Probably the lack of information available is due to two factors: the completeness of its function set and functionality on one hand, and on the other the late date in the game it was introduced (and relative high price), limiting a widespread adoption by the community.

Not sure this is still interesting but I've checked my notes on the file HEPAX file system and found this on the headers:

File headers are located atop the file. They are sequentially accessed by HEPDIR and all other filesys operations

The file headers have 14 words, as follows:

First word (lowest address): File type (1: program, 2: Data, 3: ASCII, etc...)
Next 6 words: compressed file name, up to 7 chars long
Next 2 words: File size in registers (for programs) and words (for other types)
Next 5 words: unknown purpose.

ASCII files have an EOF word a the very bottom, value "0FF"

FileSys Info

The control area is located at 0xpFE7 - 0xpFF3.
Fields are as follows:

0xFE7 : Previous HRAM page id# (aero if first)
0xFE8: Next HRAM page id# (zero if last)

0xFE9-A: next available address . Initial value = 091 / 000

0xFEB-C: current file address , Initial value - 000 / 000

0xFED-E: first file address. Initial value 091 / 000

0xFEF-F0: last file address . Initial value 091 / 000

0xFF!-2: bottom of RAM in this page. Fixed values= 0E5 / 00F

0xFF3: initialized flag. Initial value = 100, changes to 200 after initialization

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Looking forward to seeing this project develop further, looks like a wonderful design!

ÁM