AMOS file formats

Table of contents

• About the formats
• AMOS source code file format
  • Tokenised BASIC code format
    • Specially printed tokens
    • Specially sized tokens
    • Procedure decryption source code
• AMOS Sprite and Icon formats
• AMOS Memory Bank formats
  • AMOS Music Bank format
  • AMOS AMAL Bank format
  • AMOS Menu Bank format
  • AMOS Data Bank format
  • AMOS Work Bank format
  • AMOS Asm Bank format
  • AMOS Picture Bank format
  • AMOS Samples Bank format

About the formats

AMOS is the name given to a number of BASIC-like programming languages created for the Amiga by François Lionet, who is also known for the BASIC-like language STOS for the Atari ST and ClickPlay for the IBM PC. AMOS languages include "AMOS The Creator", "Easy AMOS" and "AMOS Professional".

This document attempts to cover all file formats defined by the AMOS software itself. File formats invented in third party software shall not be included. This is a first draft and many formats are not included.

All multi-byte integers are big-endian unless otherwise specified.

AMOS source code file format

AMOS source code is normally stored in a file with the extension ".AMOS". It begins with 16 bytes of ASCII text from the following list:

As you can see the upper-case "V" shows that the source code has been tested, and the lower-case "v" shows that the source code has not been tested. This refers to whether the AMOS interpreter has performed a sanity test on all lines of code, and found no syntax errors.

After the 16 byte header is a 4-byte 32-bit unsigned integer stating the number of bytes of tokenised BASIC code. This is immediately followed by the BASIC code itself, for the length given.

Finally, the 4-bytes ASCII identifier "AmBs" is given, followed by a 2-byte 16-bit unsigned integer with the number of memory banks to follow. This is followed by the banks themselves, individually sized. Each bank can either be a sprite bank, an icon bank or a regular memory bank. There is no more data in the source code file after this. If a sprite bank is given, it always occupies bank 1 and there must not be another sprite bank or regular memory bank with a bank number of 1. If an icon bank is given, it always occupies bank 2 and there must not be another icon bank or regular memory bank with a bank number of 2.

Tokenised BASIC code format

The tokenised BASIC code is a stream of tokenised lines. Each tokenised line has the following format:

• 1 byte: The length of this line in words (2 bytes), including this byte. To get the length of the line in bytes, double this value.
• 1 byte: The indent level of this line. AMOS automatically indents lines to show program structure. If printing this line as ASCII text, you should print {indent level + 1} space characters as the beginning of the line, or no spaces if the value is less than 2.
• many bytes: a sequence of tokens. Each token is at least two bytes, and all tokens are rounded to to a multiple of two bytes. Each token is individually sized. The tokens always end with a compulsory null token.

AMOS considers each token as a signed 16-bit number. Token values between 0x0000 and 0x004E are special printing and have differing sizes, all others are simply a signed offset into AMOS's internal token table. The text of the token in the internal token table is what should be printed. Some of these tokens have special size rules, all others are 2 bytes in size.

Specially printed tokens

Specially sized tokens

Procedure decryption source code

If you should find a procedure (0x0376) token with the "is encrypted" bit set, run this C function on the code and it will decrypt the contents of the procedure.

/* fetches a 4-byte integer in big-endian format */
#define EndGetM32(a)  ((((a)[0])<<24)|(((a)[1])<<16)|(((a)[2])<<8)|((a)[3]))
/* fetches a 2-byte integer in big-endian format */
#define EndGetM16(a)  ((((a)[0])<<8)|((a)[1]))

void decrypt_procedure(unsigned char *src) {
  unsigned char *line, *next, *endline;
  unsigned int key, key2, key3, size;

  /* ensure src is a pointer to a line with the PROCEDURE token on it */
  if (EndGetM16(&src[2]) != 0x0376) return;

  /* do not operate on compiled procedures */
  if (src[10] & 0x10) return;

  /* size+8+6 is the start of the line after ENDPROC */
  size = EndGetM32(&src[4]);
  endline = &src[size+8+6];
  line = next = &src[src[0] * 2];

  /* initialise encryption keys */
  key = (size << 8) | src[11];
  key2 = 1;
  key3 = EndGetM16(&src[8]);

  while (line < endline) {
    line = next;
    next = &line[line[0] * 2];

    /* decrypt one line */
    for (line += 4; line < next;) {
      *line++ ^= (key >> 8) & 0xFF;
      *line++ ^=  key       & 0xFF;
      key  += key2;
      key2 += key3;
      key = (key >> 1) | (key << 31);
    }
  }
  src[10] ^= 0x20; /* toggle "is encrypted" bit */
}

AMOS Sprite and Icon bank formats

A sprite bank and an icon bank share very similar attributes. They define graphic data which can be drawn onscreen.

• 4 bytes: "AmSp" for sprites (bank 1) or "AmIc" for icons (bank 2)
• 2 bytes: the number of sprites or icons to follow
• many bytes: the above-counted sprites or icons
• 64 bytes: a 32-entry colour palette. Each entry has the Amiga COLORx hardware register format, which is 0x0RGB, where R, G and B represent red, green and blue colour components and are between 0x0 (minimum) and 0xF (maximum).

Each sprite or icon has this format:

• 2 bytes: width, in 16-bit words
• 2 bytes: height, in raster lines
• 2 bytes: depth, in bitplanes (1 to 5)
• 2 bytes: hot-spot X co-ordinate
• 2 bytes: hot-spot Y co-ordinate
• many bytes: width*height*depth*2 bytes of planar graphic data

AMOS Memory Bank formats

An AMOS Memory bank is simply a named block of data. AMOS allows for 15 such banks in an AMOS program, and they can also be loaded and saved at runtime using the "Load" and "Save" commands. Each bank has a standard 20 byte header, although the "length" field in this header does not count the "name" field of this header as part of the header. Each bank can be located in "chip" memory, which is accessible to the Amiga's custom graphics and sound processors, or it can be located in "fast" memory, which is only accessible to the CPU. The header format is as follows:

• 4 bytes: the ASCII identifier "AmBk"
• 2 bytes: the bank number (1-15)
• 2 bytes: 0 for chip memory bank, 1 for fast memory bank
• 4 bytes: bank length, but only bits 27 to 0. Bits 28 and 29 are undefined, not part of the length field. Bit 30 means "try chip memory", bit 31 means "try fast memory" if set.
• 8 bytes: the bank name. It is always an unterminated ASCII string which is padded with spaces.

The header is followed by the bank data, which is {bank length - 8} bytes long.

AMOS Music Bank format

This bank has the name "Music" and is created with various conversion utilities shipped with AMOS. It is played back with the Music extension. See the accompanying AMOS Music file format document for more details.

AMOS AMAL Bank format

This bank has the name "Amal". It contains instructions in AMOS Animation Language format. This will be described in more detail in a later draft of this document.

AMOS Menu Bank format

This bank has the name "Menu". It contains pull-down menu definitions. This will be described in more detail in a later draft of this document.

AMOS Data Bank format

This bank has the name "Datas". It is created in AMOS using the "Reserve As Data" command, and has no specific format.

AMOS Work Bank format

This bank has the name "Work". It is created in AMOS using the "Reserve As Work" command, and has no specific format. As a Work bank, it is not saved as part of the source code, unlike normal data banks.

AMOS Asm Bank format

This bank has the name "Asm". It contains Amiga machine code that was loaded into a bank using the "Pload" command and has no specific format (other than containing MC680x0 binary code).

AMOS Picture Bank format

This bank has the name "Pac.Pic." and is created with the Compact extension's "Pack" command. See the accompanying AMOS Pac.Pic. file format document for more details.

AMOS Samples Bank format

This bank has the name "Samples" and is created with the Sample Bank Editor shipped with AMOS. The samples can be played back with the Music extension. The format of the bank is as follows:

• 20 byte: the regular bank header, as described above
• 2 bytes: the number of samples in this bank
• many bytes: A list of offsets, each 4 bytes long, to each sample. The offset is relative to the location of the "number of samples" field above.

The format of each sample is as follows:

• 8 bytes: the name for the sample, in ASCII.
• 2 bytes: the frequency of the sample in hertz.
• 4 bytes: the length of the sample in bytes.
• many bytes: the sample data itself, a stream of twos complement signed 8-bit PCM samples