The YASEP's assembly language

Or maybe the high-level assembly will simply be implemented as a side-function of listed.

The YASEP's instructions are very simple but they are not always practical, so some opcodes introduce a few modifications (see here). They are usually harmless and don't impact the architecture, but they make the instructions more handy, thus helping writing/reading programs easily.

• Rule 0 : The opcode comes first.
• Rule 1 : The destination register comes after all the source operands (usually, at the end of the instruction).
• Rule 2 : Generally, the immediate value comes just after the opcode, before the other operands (except the few cases that must obey rule#1, like FORM_Ri and FORM_RI).
• Rule 3 : The conditional codes come at the end of the instruction, after the destination register.

Input processing

• The assembly routine takes a single line (a character string with no "end of line" like '\n', '\r'...)
• The line may end with a comment, started with ';'. Starting from this delimiter, all the followin characters are flushed.
• The leading and trailing spaces are removed, the comas and tabs are replaced by spaces, and duplicated spaces are merged. You are free to write add 234h d2 r3, add 234h d2, r3 or add 234h,   d2,   r3
• The whole line is converted to upper case. So it does not matter if you write adD 234h D2 r3 or ADd 234h d2 R3 because it will become ADD 234H D2 R3 internally.
• The first word must be the opcode.
• Depending on the instruction, register names, keywords and/or constant numbers follow. The order and function of these parameters are defined by the "form".

and that's all there is to say about the subject of "input syntax".

• Hexadecimal ([0-9A-F]* with a trailing 'h'), for example dw 1234h (the 0x prefix or the $ prefix is never used)
• Decimal ([0-9]* without prefix or suffix) : dw 1234.
  This is the only format that accepts a leading minus sign : dw -1234
• Binary ([01]* with a trailing 'b') : dw 01101101b

Numbers are mostly used in contexts where the number of significant bits is bounded to the size of the container (usually, the immediate fields). When more bits are input, the assembler keeps only the desired number of LSB, and discards the MSB. The following example shows how the number is truncated : db 1234h.

• DB : "Data Byte"
      outputs 8 bits : db 12h
• DH : "Data Half-word"
      outputs 16 bits : dh 1234h
• DW : "Data Word"
      output 32 bits : dw 12345678h

An unbounded number of litteral numbers is accepted (since 2007-04-04 and the limit depends on the JavaScript engine, not on the assembler's design). The floating assembler's window will not display all the digits when more than 32 bits are given but they are available through software (by defining the emit_bin() function).

Example : db 12h 34h 56h 78h 9Ah BCh DEFh
emit_bin()'s output :

The ability to include ASCII strings is still missing at this time of writing.

Since 2008-08, the YASEP exists in 16-bit and 32-bit variants. The opcodes don't change but a few of them are pointless in 16-bit mode or 32-bit mode. The source code can specify that a certain width is used so a warning is issued when a pointless instruction (probably invalid for the given CPU) is assembled.

YASEP16 specifies that the targetted CPU has a 16-bit datapath. All 32-bit only instructions generate a warning.

YASEP32 specifies that the targetted CPU has a 32-bit datapath. All 16-bit only instructions generate a warning.

YASEP resets the target CPU to generic/undefined.

These pseudo-instructions don't generate any code and can be used in any order, as they simply control an internal flag. This flag is compared with each instruction's flag (see YASEP32_ONLY and YASEP16_ONLY below).

• Register names (NPC R0 R1 R2 R3 R4 A0 D0 A1 D1 A2 D2 A3 D3 A4 D4)
• Pseudo-instructions (DB DH DW YASEP16 YASEP32 YASEP)
• The condition codes (LSB0 LSB1 MSB0 MSB1 ZERO NZ)
• The instruction opcodes and the opcode aliases ()

There are two types of aliases : form aliases (see ALIAS_RR) and instruction aliases (they are listed under the opcode map). This section is about instruction aliases.

Internally, they can be used like normal instructions, but they provide different forms and/or different semantics. However, they use real opcodes of other instructions. The substitution is handled at the assembly level and the disassembly probably won't infer the originally assembled alias. So don't be surprised if instructions like NOT or NEG assemble correctly, but the disassembly returns a different opcode.