Description:
BSPEC stands for "Begin Special Mode" and ESPEC stands for "End Special Mode".
The assembler writes the text between these two instructions directly to the output file, but does not load it as part of the assembled program. This mechanism can be used to transmit information from the source to the object file for later use. For instance high level languages might embed debug information into the object file.
Regular MMIX instructions are not allowed in special mode, however, the pseudo instructions IS, PREFIX, BYTE, WYDE, TETRA, OCTA, GREG, and LOCAL are allowed.
The Expression following BSPEC should fit into two byte and can be used to pass information regarding format and type of the following information. For example BSPEC 1 might be used to pass source line numbers and BSPEC 2 for source file names.