SpecServer/SerialServ file mapping ================================== Native ------ BBC load and execution addresses hold Spectrum load and execution addresses, and the Spectrum filetype: BBC Spectrum Load Addr b0-b15 <-> Start Addr (autorun line, array name, load address) Exec Addr b0-b15 <-> Parameter Addr (VARS-PROG, execution address) Length <-> Length Load/Exec b16-b17 <-> File type On loading, the Spectrum filetype is formed by reading b16-17 from the BBC load address and adding 4 times the difference between b16-17 of the BBC load address and b16-b17 of the execution address. On saving, b0-1 of the Spectrum filetype is stored in b16-17 of the BBC load address and the filetype divided by 4 is subtracted from b0-b1 and stored in b16-b17 of the BBC execution address. This results in Spectrum filetypes 0, 1, 2 and 3 being reflected in the load and execution address high bytes being the same, as here: LoadAddr ExecAddr &0000xxxx &0000xxxx -> Type 0 (BASIC) &0001xxxx &0001xxxx -> Type 1 (NumArray) &0002xxxx &0002xxxx -> Type 2 (CharArray) &0003xxxx &0003xxxx -> Type 3 (Code) Any more Spectrum filetypes would be encoded as follows: &0000xxxx &0001xxxx -> Type 4 &0001xxxx &0002xxxx -> Type 5 &0002xxxx &0003xxxx -> Type 6 &0003xxxx &0000xxxx -> Type 7 &0000xxxx &0002xxxx -> Type 8 &0001xxxx &0003xxxx -> Type 9 &0002xxxx &0000xxxx -> Type 10 &0003xxxx &0001xxxx -> Type 11 &0000xxxx &0003xxxx -> Type 12 &0001xxxx &0000xxxx -> Type 13 &0002xxxx &0001xxxx -> Type 14 &0003xxxx &0002xxxx -> Type 15 Tapefile -------- File is filetyped to "TAPE" (DOS ".TAP"), type &11D (BBC load address is &FFF11Dxx) or to Speculator "SpecTape" (DOS ".SPT"), type &701 (BBC load address &FFF701xx). The file contains the file information header prefixed to the file data, as follows for a TAPE file: Byte Content 0-1: &0013 - Length of header, ignored on loading 2: &00 - Header type, ignored on loading 3: File type: &00=Basic, &01=NumArray, &02=CharArray, &03=Code, etc. 4-13: Filename, duplicate of leafname on saving, ignored on loading 14-15: Length of data, lo-hi - ignored on loading 16-17: Start address, lo-hi (load address) 18-19: Extra address, lo-hi (exec address) 20: Header checksum, ignored on loading 21-22: &nnnn - Length of data portion, ignored on loading 23: &FF - Data type, ignored on loading 24...: Actual data 25+len: Data checksum, ignored on loading A Speculator SpecTape file is the same, but the length fields are two less - eg, bytes 0/1 contain &0011 - and the checksum bytes are omitted, so the data starts at byte 23. The embedded header and data length, type and checksum, as well as the embedded filename and file length are written correctly when saving, but are ignored when loading. The checksums are generated by XORing all the bytes from after the length (byte 2 or byte 23) to before the checksum (byte 19 or byte 24+len). The server program only fetches the first entry in a tapefile. Load Address ------------ This is the "parameter 1" or "start" field in the Spectrum file header. For a Basic program it is the autorun line if <&8000. For a Code file, it is the address to load to if none is specified. For an array the high byte is the array name. Execution Address ----------------- This is the "parameter 2" or "extra" field in the Spectrum file header. For a Basic program it is VARS-PROG, the length of the Basic program before the variables. For a Code file it is the start address the code is executed from if RUN as machine code. Running Machine Code -------------------- When a piece of machine code is loaded and run it is entered with the registers in the following state: BC= entry address DE=>command tail HL= undefined Cy=1 A,Z=undefined If a file's load address is &0000 it is loaded to a temporarily allocated piece of memory. It's execution address is taken as the offset from the start of the code at which to enter. This is useful for small transient utilities. If it is small enough, transient code is run on the stack. Where the transient memory is, and what the system thinks is "small enough" are system-specific and may change from time to time, including within a running system. File Headers ------------ The load and execution addresses are store in the order they occur in the tape header. Interface 1 headers hold the information in a slightly different order. These diagrams show where the addresses are expected. (LOAD) means that on reading this field is filled with the load address; but this field is ignored when writing. Tape Header Interface 1 Header ----------- ------------------ Type 00 - BASIC 00 01 - - 0A 0B 0C 0D 0E 0F 10 00 01 02 03 04 05 06 07 08 +--+--- -- ---+--+--+---+--+---+--+ +--+--+--+---+--+---+--+---+--+ |00| Filename | LEN | LOAD | EXEC | |00| LEN |(LOAD)| EXEC | LOAD | +--+--- -- ---+--+--+---+--+---+--+ +--+--+--+---+--+---+--+---+--+ Length --+ | | Length --+ | | Autostart line -----+ | VARS-PROG -----+ | VARS-PROG --------+ Autostart line -------+ Type 01 - Number Array 00 01 - - 0A 0B 0C 0D 0E 0F 10 00 01 02 03 04 05 06 07 08 +--+--- -- ---+--+--+---+--+---+--+ +--+--+--+---+--+---+--+---+--+ |01| Filename | LEN | LOAD | EXEC | |01| LEN | EXEC | LOAD |(LOAD)| +--+--- -- ---+--+--+---+--+---+--+ +--+--+--+---+--+---+--+---+--+ Length --+ | Length --+ | Array name -----+ Array name -----+ Type 02 - Character Array 00 01 - - 0A 0B 0C 0D 0E 0F 10 00 01 02 03 04 05 06 07 08 +--+--- -- ---+--+--+---+--+---+--+ +--+--+--+---+--+---+--+---+--+ |02| Filename | LEN | LOAD | EXEC | |02| LEN | EXEC | LOAD |(LOAD)| +--+--- -- ---+--+--+---+--+---+--+ +--+--+--+---+--+---+--+---+--+ Length --+ | Length --+ | Array name -----+ Array name -----+ Type 03 - CODE 00 01 - - 0A 0B 0C 0D 0E 0F 10 00 01 02 03 04 05 06 07 08 +--+--- -- ---+--+--+---+--+---+--+ +--+--+--+---+--+---+--+---+--+ |03| Filename | LEN | LOAD | EXEC | |03| LEN | LOAD | EXEC |(LOAD)| +--+--- -- ---+--+--+---+--+---+--+ +--+--+--+---+--+---+--+---+--+ Length --+ | | Length --+ | | Start address -----+ | Start address --+ | Execution address --------+ Execution address -----+ History ------- 1.00 12-04-88 Initial version. 1.10 15-03-92 Added support for TAPE files.