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# D10V Dependent Features

- D10V-Opts: D10V Options
- D10V-Syntax: Syntax
- D10V-Float: Floating Point
- D10V-Opcodes: Opcodes

## D10V Options

The Mitsubishi D10V version of `as` has a few machine dependent options.

``-O'`
  The D10V can often execute two sub-instructions in parallel. When this option is used, `as` will attempt to optimize its output by detecting when instructions can be executed in parallel.

## Syntax

The D10V syntax is based on the syntax in Mitsubishi's D10V architecture manual. The differences are detailed below.

- D10V-Size: Size Modifiers
- D10V-Subs: Sub-Instructions
- D10V-Chars: Special Characters
- D10V-Regs: Register Names
- D10V-Addressing: Addressing Modes
- D10V-Word: @WORD Modifier

### Size Modifiers

The D10V version of `as` uses the instruction names in the D10V Architecture Manual. However, the names in the manual are sometimes ambiguous. There are instruction names that can assemble to a short or long form opcode. How does the assembler pick the correct form? `as` will always pick the smallest form if it can. When dealing with a symbol that is not defined yet when a line is being assembled, it will always use the long form. If you need to force the assembler to use either the short or long form of the instruction, you can append either ``.s'` (short) or ``.l'` (long) to it. For example, if you are writing an assembly program and you want to do a branch to a symbol that is defined later in your program, you can write ``bra.s foo'`. Objdump and GDB will always append ``.s'` or ``.l'` to instructions which have both short and long forms.

### Sub-Instructions

The D10V assembler takes as input a series of instructions, either one-per-line, or in the special two-per-line format described in the next section. Some of these instructions will be short-form or sub-instructions. These sub-instructions can be packed into a single instruction. The assembler will do this automatically. It will also detect when it should not pack instructions. For example, when a label is defined, the next instruction will never be packaged with the previous one. Whenever a branch and link instruction is called, it will not be packaged with the next instruction so the return address will be valid. Nops are automatically inserted when necessary.

If you do not want the assembler automatically making these decisions, you can control the packaging and execution type (parallel or sequential) with the special execution symbols described in the next section.

### Special Characters

``;'` and ``#'` are the line comment characters. Sub-instructions may be executed in order, in reverse-order, or in parallel. Instructions listed in the standard one-per-line format will be executed sequentially. To specify the executing order, use the following symbols:

``->'`
  Sequential with instruction on the left first.
``<-'`
  Sequential with instruction on the right first.
``||'`
  Parallel

The D10V syntax allows either one instruction per line, one instruction per line with the execution symbol, or two instructions per line. For example

`abs a1 -> abs r0`
  Execute these sequentially. The instruction on the right is in the right container and is executed second.
`abs r0 <- abs a1`
  Execute these reverse-sequentially. The instruction on the right is in the right container, and is executed first.
`ld2w r2,@r8+ || mac a0,r0,r7`
  Execute these in parallel.
`ld2w r2,@r8+ ||`
`mac a0,r0,r7`
  Two-line format. Execute these in parallel.
`ld2w r2,@r8+`
`mac a0,r0,r7`
  Two-line format. Execute these sequentially. Assembler will put them in the proper containers.
`ld2w r2,@r8+ ->`
`mac a0,r0,r7`
  Two-line format. Execute these sequentially. Same as above but second instruction will always go into right container.

Since ``$'` has no special meaning, you may use it in symbol names.

### Register Names

You can use the predefined symbols ``r0'` through ``r15'` to refer to the D10V registers. You can also use ``sp'` as an alias for ``r15'`. The accumulators are ``a0'` and ``a1'`. There are special register-pair names that may optionally be used in opcodes that require even-numbered registers. Register names are not case sensitive.

Register Pairs

`r0-r1`
`r2-r3`
`r4-r5`
`r6-r7`
`r8-r9`
`r10-r11`
`r12-r13`
`r14-r15`

The D10V also has predefined symbols for these control registers and status bits:

`psw`
  Processor Status Word
`bpsw`
  Backup Processor Status Word
`pc`
  Program Counter
`bpc`
  Backup Program Counter
`rpt_c`
  Repeat Count
`rpt_s`
  Repeat Start address
`rpt_e`
  Repeat End address
`mod_s`
  Modulo Start address
`mod_e`
  Modulo End address
`iba`
  Instruction Break Address
`f0`
  Flag 0
`f1`
  Flag 1
`c`
  Carry flag

### Addressing Modes

`as` understands the following addressing modes for the D10V. `Rn` in the following refers to any of the numbered registers, but not the control registers.

`Rn`
  Register direct
`@Rn`
  Register indirect
`@Rn+`
  Register indirect with post-increment
`@Rn-`
  Register indirect with post-decrement
`@-SP`
  Register indirect with pre-decrement
`@(disp, Rn)`
  Register indirect with displacement
`addr`
  PC relative address (for branch or rep).
`#imm`
  Immediate data (the ``#'` is optional and ignored)

### @WORD Modifier

Any symbol followed by `@word` will be replaced by the symbol's value shifted right by 2. This is used in situations such as loading a register with the address of a function (or any other code fragment). For example, if you want to load a register with the location of the function `main` then jump to that function, you could do it as follws:

    ldi     r2, main@word
    jmp     r2

## Floating Point

The D10V has no hardware floating point, but the `.float` and `.double` directives generates IEEE floating-point numbers for compatibility with other development tools.

## Opcodes

For detailed information on the D10V machine instruction set, see D10V Architecture: A VLIW Microprocessor for Multimedia Applications (Mitsubishi Electric Corp.). `as` implements all the standard D10V opcodes. The only changes are those described in the section on size modifiers

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