Format of Flash and ROM SSD cards
This document describes information about the structure of existing types of Flash and ROM SSDs. It does not apply to RAM cards as they use FAT16. 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.
trip values are offsets from the start of the card. The term "NULL" means the value
Flash and ROM cards always begin with:
|2||4||unique ID of SSD|
|6||2||unknown (only ever seen 1)|
|8||3||unknown (only ever seen 1)|
|11||3||pointer to the root directory entry|
|25||4||count of times flash card has been formatted, or
|29 (Flash only)||2||size of the card in 256 byte units (i.e.
|31 (Flash only)||2||unknown (only ever seen
|33 (Flash only) or 29 (ROM only)||Until
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 IDs. 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
0xFF byte. The identity strings seen to date are:
PSION 1.0 01/80
PSION 1.0 06/80
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
The root directory entry is a filing system record. The directory name is
File and folder entries
Filesystem 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:
|0||3||Pointer to the next entry in same directory|
|15||3||Pointer to first entry record|
|18||3||Pointer to alternate record|
|26 (File only)||3||Pointer to start of first data record|
|29 (File only)||2||Length of first data record|
Flags and Properties
The flags are as follows:
|0||entry deleted||entry still valid|
|1||properties, time, and date valid|
|2||directory||file or volume name|
|3||no entry record (so NULL at offset 15)|
|4||no alternate record (so NULL at offset 18)|
|5||no more entries in same directory (so NULL at offset 0)|
|6||all entries seen so far have this bit set to 1|
|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:
|3||Is a volume name|
|4||Is a directory|
Time and Date Codes
The time code is:
0x800 * hour + 0x20 * minute + second / 2
The date code is:
0x200 * (year - 1980) + 0x20 * 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:
|0||1||Flags (as above)|
|1||3||pointer to next continuation record|
|4||3||pointer to alternate continuation record|
|7||3||pointer to data record|
|10||2||length of data record, or
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 EPOC16, 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 reorganised 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 initialise 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))
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.