PSIONICS FILE - FLASH
=====================
Format of Flash SSD cards and ROMs
Last modified 1994-09-12
==================================
This file describes information about the structure of existing types of
Flash cards. It does not apply to RAM cards, and might not apply to new types
of SSDs that may become available in the future. It does, however, appear to
apply to the ROM in the 3-Link pod and the SSD ROM used to ship the
Spreadsheet.
The term "erased flash card" is one that was partially formatted, after which
the format was stopped, and then reformatted. This causes the contents of the
start of the flash card, which is normally preserved by the formatting process
(see Psionics file FILEIO) to be lost.
All "trip" values are offsets from the start of the card. The term "NULL"
means the value $FFFFFF.
The flash card always begins with:
Offset 0 (word): $F1A5 ('Flas')
Offset 2 (long): unique ID of SSD
Offset 6 (word): unknown @only ever seen 1@
Offset 8 (trip): unknown @only ever seen 1@
Offset 11 (trip): pointer to the root directory entry
Offset 14 to 21: volume name
Offset 22 to 24: volume extension
Offset 25 (long): count of times flash card has been formatted, or
$FFFFFFFF for ROMs
It then continues with either:
Offset 29 (word): size of the card in 256 byte units (i.e. $1000 = 1Mb)
Offset 31 (word): unknown @only ever seen $FFFF@
Offset 33 onward: identity string
Or:
Offset 29 onward: identity string
The first form is seen on flash cards, and the second on ROMs and erased flash
cards.
The unique ID is placed there when the SSD is first created, and is preserved
even when the SSD is formatted. There is no obvious pattern to the ID's.
Note that different 3-Link pods have different unique IDs.
If the first byte of the volume name is 00, the volume name is not in
offsets 14 to 24, but is instead found in a special file record within the
root directory.
The identity string is terminated by a zero byte or a $FF byte. The identity
strings seen to date are:
"PSION 1.0 01/80"
"PSION 1.0 06/80"
"PSION 1.0"
"Copyright (c) Psion Plc 1991"
The first two were seen on flash cards, the third on an erased flash card,
and the last on both the 3-Link pod ROM and the spreadsheet SSD ROM.
The rest of the flash card is divided into records (unused portions of the
card are full of $FF bytes).
The root directory entry is a filing system record. The directory name is
"ROOT.".
Filing system records represent entries in directories: other directories,
files, and volume names. A filing system record is 31 bytes if it represents
a file, and 26 bytes otherwise:
Offset 0 (trip): pointer to the next entry in same directory
Offset 3 to 10: entry name
Offset 11 to 13: entry extension
Offset 14 (byte): flags
Offset 15 (trip): pointer to first entry record
Offset 18 (trip): pointer to alternate record
Offset 21 (byte): entry properties
Offset 22 (word): time code
Offset 24 (word): date code
Offset 26 (trip): (file only) pointer to start of first data record
Offset 29 (word): (file only) length of first data record
The flags are as follows:
Bit 0: 1 = entry still valid, 0 = entry deleted
Bit 1: 1 = properties, time, and date valid
Bit 2: 1 = file or volume name, 0 = directory
Bit 3: 1 = no entry record (so NULL at offset 15)
Bit 4: 1 = no alternate record (so NULL at offset 18)
Bit 5: 1 = no more entries in same directory (so NULL at offset 0)
Bit 6: all entries seen so far have this bit set to 1
Bit 7: all entries seen so far have this bit set to 1
The first entry record is:
for files: first continuation record of file; if the pointer is NULL,
the file only contains one data record
for directories: filing system record of first directory entry; if the
pointer is NULL, the directory is empty
for volume names: all entries seen so far have a NULL pointer
If the alternate record exists, then most of the data in the record pointing
to the alternate record should be ignored, and replaced by the corresponding
data in the alternate record. The alternate record is:
for files: a continuation record; ignore the first entry record
and the data record in the original record
for directories: alternate records are not used
for volume names: alternate records are not used
The entry properties are:
Bit 0: 1 = read-only file
Bit 1: 1 = hidden file
Bit 2: 1 = system file
Bit 3: 1 = is a volume name
Bit 4: 1 = directory
Bit 5: 1 = modified
The time code is: $800 * hour + $20 * minute + second / 2.
The date code is: $200 * (year - 1980) + $20 * month + date.
A file is represented by a linked list of records. The first record is the
filing system record, or its alternate, and the remaining records are all
continuation records. A continuation record is 17 bytes:
Offset 0 (byte): flags (as above)
Offset 1 (trip): pointer to next continuation record
Offset 4 (trip): pointer to alternate continuation record
Offset 7 (trip): pointer to data record
Offset 10 (word): length of data record, or $FFFF if it is unknown and the
file is still open
Offset 12 (byte): entry properties
Offset 13 (word): time code
Offset 15 (word): date code
Note that bits 5, 2, and 0 of the flags will always be set, and that bits 4
and 3 refer to offsets 1 and 4 respectively. In addition, it is possible for
bit 3 to be clear but for there to be no next continuation record.
To examine all the data in a file, start at the filing system record, and then
proceed as follows for each record in turn:
If flag bit 4 is set, go to the alternate record and repeat this step.
Otherwise the next part of the file is given by the data pointer and length
within this record.
After using the data: if flag bit 3 is clear and the next continuation
record pointer is not null, go to that record, starting by examining flag
bit 4. Otherwise the end of file has been reached.
As files are modified, the records on the flash card become out of date.
For example, data that has been overwritten will remain on the card. In
particular, the properties, time, and date bytes of records will remain even
when they are not valid (as indicated by flag bit 1). Also note that a
change to a file may cause several continuation records to be written at the
same time. In these circumstances, only one of these will have the correct
properties, time, and date, and the others will be written without them, and
with some other record overlapping these 5 bytes.
Reading flash cards
-------------------
On later versions of EPOC, flash cards can be read with FilLocReadPDD (see
Psionics file SYSCALLS). If this is not available, the following code can be
used to read flash cards. The left four columns give individual bytes; the
right column is the bytes reorganized as long words.
EB 3A 55 E8 E8553AEB
95 00 83 EC EC830095
0E 8B F4 8D 8DF48B0E
7E 28 BA 21 21BA287E
DD 2B DB B4 B4DB2BDD
0A CD 85 83 8385CD0A
C4 0E 8B D8 D88B0EC4
B4 02 CD 85 85CD02B4
89 46 00 89 89004689
5E 02 CD 8F 8FCD025E
8C 46 32 B4 B432468C
00 CD 88 80 8088CD00
E4 0F 89 46 46890FE4
30 9C FA 1E 1EFA9C30
07 9D 5D CB CB5D9D07
83 FB 04 72 7204FB83
05 B8 FC FF FFFCB805
EB 51 8B F0 F08B51EB
55 E8 4F 00 004FE855
88 5E 20 FF FF205E88
36 12 00 8D 8D001236
46 04 A3 12 12A30446
00 FF 36 20 2036FF00
00 80 26 20 20268000
00 00 E4 14 14E40000
C4 7E 30 26 26307EC4
FE 45 0D 1E 1E0D45FE
07 8B FA B0 B0FA8B07
00 FF 5E 00 005EFF00
98 8B D8 C4 C4D88B98
7E 30 26 FE FE26307E
4D 0D 9C FA FA9C0D4D
1E 07 9D 8F 8F9D071E
06 20 00 80 80002006
3E 20 00 00 0000203E
74 02 E6 14 14E60274
8B C3 8F 06 068FC38B
12 00 5D CB CB5D0012
58 FF E0 E8 E8E0FF58
FA FF 05 06 0605FFFA
00 8B E8 C3 C3E88B00
00 00 00 00 00000000
00 00 00 00 00000000
00 00 00 00 00000000
00 00 00 00 00000000
00 00 00 00 00000000
00 00 00 00 00000000
00 00 00 00 00000000
00 00 00 00 00000000
00 00 00 00 00000000
00 00 00 00 00000000
4C 4F 43 2E 2E434F4C
54 59 31 00 00315954
00 00 00 00 00000000
If this code is placed at location bin%, then to initialize the code, call
USR (bin% + 2, 0, 0, 0, 0)
Then, to copy date from the flash card:
rc% = USR (bin%, ADDR (loc&), drive%, length%, ADDR (buffer))
copies length% bytes into the buffer, starting from address loc& on card
drive% (0 is A:, 1 is B:, 2 is C:, etc.). A returned value of 0 indicates
success.
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