HP-41 and Hepax Filesystem

[Sylvain Cote]

I never found that information but I did spent some time reverse engineering it.

HEPAX file header uses 10 bytes
HEPAX data record use 6 bytes

4K page structure (warning: it may contains errors) [P means page address -> P001 could be 8001, 9001, etc]

Code:

P000  00B  < XROM Number (ROM assign an unused ID)
P001  000  < CAT Entry 00
P002  000  / FAT Space (64 fn + eof)
...        | (64*2)+2 = 130d = 82h
P083  000  \ Unused by HEPAX
P084  000  / Unused by HEPAX
P08F  000  \

Code:

P090  000  / 
...        | HEPAX DATA
PFE5  000  \

Code:

PFE6  000  < ? spacer ?
PFE7  000  < HEPAX pages linked list: prev page (0 = end of list)
PFE8  009  < HEPAX pages linked list: next page (0 = end of list)
PFE9  091  / Address of the first file in page
PFEA  000  \ 0091
PFEB  000  / Address of the active File
PFEC  000  \ 0000 (0000 = None)

Code:

PFED  090  / Start of usable page address
PFEE  000  \ 0090
PFEF  091  / Next file free space address
PFF0  000  \ 0091
PFF1  0E5  / End of usable page address
PFF2  00F  \ 0FE5
PFF3  200  < ? marker ? 512 what ?

Code:

PFF4  000  IVT Pause Loop
PFF5  000  IVT Main Running Loop
PFF6  000  IVT Deep Sleep Wake up, no key down
PFF7  000  IVT Off
PFF8  000  IVT I/O Service
PFF9  000  IVT Deep Sleep Wake up
PFFA  000  IVT Cold Start

Code:

PFFB  000  /
PFFC  000  | ROM Trailer
PFFD  000  | 
PFFE  000  \ 
PFFF  000  < Checksum