Blackfin汇编语言之程序流程控制

Blackfin常用指令均摘录自blackfin编程参考手册，以方便查阅。

Blackfin流程控制指令有：

  1. jump
  2. if CC jump
  3. call
  4. rts, rti, rtx, rtn, rte
  5. lsetup, loop

分别简介之。

   * jump

     General Form
       JUMP (destination_indirect)
       JUMP (PC + offset)
       JUMP offset
       JUMP.S offset
       JUMP.L offset
    
     Syntax
       JUMP ( Preg ) ;
       /*indirect to an absolute (not PC-relative)address(a)*/
       JUMP ( PC + Preg ) ; /* PC-relative, indexed (a)*/
       JUMP pcrel25m2 ; /* PC-relative, immediate (a) or (b)*/
       JUMP.S pcrel13m2 ; /*PC-relative, immediate, short (a)*/
       JUMP.L pcrel25m2 ; /* PC-relative, immediate, long (b)*/
       JUMP user_label ;
       /* user-defined absolute address label,resolved by the 
        assembler/linker to the appropriate PC-relative 
        instruction (a) or (b) */
       
     Syntax Terminology
       Preg: P5–0, SP, FP
       pcrelm2: undetermined 25-bit or smaller signed, even
             relative offset, with a range of –16,777,216
             through 16,777,214 bytes
             (0xFF00 0000 to 0x00FF FFFE)
       pcrel13m2: 13-bit signed, even relative offset, with a
             range of –4096 through 4094 bytes (0xF000 to
             0x0FFE)
       pcrel25m2: 25-bit signed, even relative offset, with a
             range of –16,777,216 through 16,777,214 bytes
             (0xFF00 0000 to 0x00FF FFFE)
       user_label: valid assembler address label, resolved by
             the assembler/linker to a valid PC-relative offset
      
     注：1。(a)16bit指令长度，(b)32bit指令长度
            (bp)Branch Prediction
         2。跳转地址必须偶地址对齐(16bit-address)

   * if cc jump
      
     General Form
       IF CC JUMP destination
       IF !CC JUMP destination
      
     Syntax
       IF CC JUMP pcrel11m2 ;
       /* branch if CC=1, branch predicted as not taken (a)*/
       IF CC JUMP pcrel11m2 (bp) ;
       /* branch if CC=1, branch predicted as taken (a) */
       IF !CC JUMP pcrel11m2 ;
       /* branch if CC=0, branch predicted as not taken (a)*/
       IF !CC JUMP pcrel11m2 (bp) ;
       /* branch if CC=0, branch predicted as taken (a) */
       IF CC JUMP user_label ;
       /*user-defined absolute address label, resolved by the 
        assembler/linker to the appropriate PC-relative 
        instruction (a) */
       IF CC JUMP user_label (bp) ;
       /* user-defined absolute address label, resolved by the 
        assembler/linker to the appropriate PC-relative 
        instruction (a) */
       IF !CC JUMP user_label ;
       /* user-defined absolute address label, resolved by the 
        assembler/linker to the appropriate PC-relative 
        instruction(a) */
       IF !CC JUMP user_label (bp) ;
       /* user-defined absolute address label, resolved by the 
        assembler/linker to the appropriate PC-relative 
        instruction (a) */
    
     Syntax Terminology
       pcrel11m2: 11-bit signed even relative offset, with a
            range of –1024 through 1022 bytes (0xFC00 to 0x03FE)
            this value can optionally be replaced with an
            address label that is evaluated and replaced during
            linking.
       user_label: valid assembler address label, resolved by
            the assembler/linker to a valid PC-relative offset

   * call
  
      General Form
        CALL (destination_indirect)
        CALL (PC + offset)
        CALL offset
     
      Syntax
        CALL ( Preg ) ;
       /*indirect to an absolute (not PC-relative) address (a)*/
        CALL ( PC + Preg ) ; /* PC-relative, indexed (a) */
        CALL pcrel25m2 ; /* PC-relative, immediate (b) */
        CALL user_label ; /*user-defined absolute address label,
         resolved by the assembler/linker to the appropriate 
         PC-relative instruction (a) or (b) */
       
      Syntax Terminology
        Preg: P5–0, SP, FP
        pcrel25m2: 25-bit signed, even, PC-relative offset; can
           be specified as a symbolic address label, with a
           range of –16,777,216 through 16,777,214 (0xFF00 0000
           to 0x00FF FFFE) bytes.
        user_label: valid assembler address label, resolved by
           the assembler/linker to a valid PC-relative offset
       
    * RTS, RTI, RTX, RTN, RTE (Return)
   
      General Form
        RTS, RTI, RTX, RTN, RTE
       
      Syntax
        RTS ; // Return from Subroutine (a)
        RTI ; // Return from Interrupt (a)
        RTX ; // Return from Exception (a)
        RTN ; // Return from NMI (a)
        RTE ; // Return from Emulation (a)
     
      Types of Return Instruction


     
    * LSETUP, LOOP
   
    General Form
      There are two forms of this instruction. The first is:

      LOOP loop_name loop_counter
      LOOP_BEGIN loop_name
      LOOP_END loop_name
     
      The second form is:
     
      LSETUP (Begin_Loop, End_Loop)Loop_Counter
     
    Syntax
      For Loop0
     
      LOOP loop_name LC0 ; /* (b) */
      LOOP loop_name LC0 = Preg ; /*autoinitialize LC0 (b)*/
      LOOP loop_name LC0 = Preg >> 1 ; /* autoinit LC0(b) */
      LOOP_BEGIN loop_name ;
      /* define the 1st instruction of loop(b)*/
      LOOP_END loop_name ;
      /* define the last instruction of the loop (b) */
      /* use any one of the LOOP syntax versions with a 
       LOOP_BEGIN and a LOOP_END instruction. The name of the 
       loop (“loop_name” in the syntax) relates the three 
       instructions together. */
      LSETUP ( pcrel5m2 , lppcrel11m2 ) LC0 ; /* (b) */
      LSETUP ( pcrel5m2 , lppcrel11m2 ) LC0 = Preg ;
      /* autoinitialize LC0 (b) */
      LSETUP ( pcrel5m2 , lppcrel11m2 ) LC0 = Preg >> 1 ;
      /* autoinitialize LC0 (b) */
     
      For Loop1
     
      LOOP loop_name LC1 ; /* (b) */
      LOOP loop_name LC1 = Preg ; /* autoinitialize LC1 (b)*/
      LOOP loop_name LC1 = Preg >> 1;/*autoinitialize LC1 (b)*/
      LOOP_BEGIN loop_name ;
      /* define the first instruction of the loop (b) */
      LOOP_END loop_name ;
      /* define the last instruction of the loop (b) */
      LSETUP ( pcrel5m2 , lppcrel11m2 ) LC1 ; /* (b) */
      LSETUP ( pcrel5m2 , lppcrel11m2 ) LC1 = Preg ;
      /* autoinitialize LC1 (b) */
      LSETUP ( pcrel5m2 , lppcrel11m2 ) LC1 = Preg >> 1 ;
      /* autoinitialize LC1 (b) */
     
    Syntax Terminology
      Preg: P5?b>C0 (SP and FP are not allowed as the source
         register for this instruction.)
      pcrel5m2: 5-bit unsigned, even, PC-relative offset; can
         be replaced by a symbolic label. The range is 4 to 30.
      lppcrel11m2: 11-bit unsigned, even, PC-relative offset
         for a loop; can be replaced by a symbolic label. The
         range is 4 to 2046 (0x0004 to 0x07FE).
      loop_name: a symbolic identifier
  
    Blackfin包含两组寄存器用于硬件循环：
    Loop_Top (LTx)： LT0,LT1
    Loop_Bottom (LBx): LB0,LB1
    Loop_Count (LCx): LC0,LC1