Aseba Specification 001

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AS001: Bytecode serialisation

This specification describes the bytecode serialisation format.

Status

Deployed since commit a017da2f.

Written by

Stéphane Magnenat and Philippe Rétornaz

File structure and extension

The file is a binary file, in which words are 16-bit integers in little endian. The extension shall be "abo".

Memory layout

address	field type	length	content
0x0	null-terminated string	4	"ABO\0"
0x4	word	2	binary format version (currently: 0)
0x6	word	2	aseba protocol version
0x8	word	2	product id
0xA	word	2	firmware version
0xC	word	2	node id
0xE	word	2	CRC-16 of node name
0x10	word	2	CRC-16 of VM description (see below)
0x12	word	2	len: length of bytecode in words
0x14	array of words	2 * len	bytecode data
0x14 + 2 * len	word	2	CRC-16 of bytecode data

To compute CRC, we use the CRC-CCITT variant. When a value is on 8 bits, we pad the MSB with 0. If a value is signed, the CRC is applied on the bits directly considering the value as unsigned. We define the CRC of a string or of an array as the sequential application of CRC to every element of the string/array. Note that we do not use the length of the string/array, as applying the CRC to every element already captures the length.

CRC-16 of VM description

We compute the CRC with the following algorithm:

crc = 0
crc C= bytecodeSize
crc C= variablesSize
crc C= stackSize
for (varLength, varName) in namedVariables:
    crc C= varLength
    crc C= varName
for (eventName) in localEvents:
    crc C= eventName
for (funcName, funcArgs) in nativeFunctions:
    crc C= funcName
    for (argLength, argName) in funcArgs:
        crc C= argLength
        crc C= argName

where a C= b is a shortcut for a = CRC(a, b) and CRC is the CRC-16 poly: 0x1021, init 0x0