Freescale Semiconductor StarCore SC140 - Manual (Page 260)

7-10 SC140 DSP Core Reference Manual
Static Programming Rules
Example 7-8 Duplicate Register Destinations
move.w #$1234,d0.h move.w #$5678,d0.l ;not allowed
bmset #3,sr.h bmset #4,sr.l ;not allowed
Note that BMSET #$3,SR.H reads and writes the 32-bit SR register.
• MOVE-like instructions that write the SR or EMR register cannot be grouped in a VLES with
instructions that affect individual status bits in the same register.
Example 7-9 Duplicate SR/EMR Register Destinations
pop sr add d0,d1,d2 ;not allowed - C bit is written twice
ift pop sr iff add d0,d1,d2 ;allowed
pop sr bmtstc #$3,d0.l ;not allowed - T bit is written twice
add d0,d1,d2 bmset #$0040,emr.l ;not allowed - DOVF is written twice
add d0,d1,d2 bmset #$0040,emr.h ;not allowed - DOVF is written twice
Note that BMSET #$3,SR.H reads and writes the 32-bit SR register, while BMTSTC #$3,D0.L
affects only the T status bit in SR.
• Multiple instructions that affect the same status bit (T, VF0-3, DI, LF0-3, or SLF bits in SR) cannot
be grouped in a VLES.
Example 7-10 Duplicate Status Bit Destinations
cmpeq d0,d1 tstgea.l r0 ;not allowed - multiple T bit updates
cmpeq d0,d1 bmtstc #$3,d0.l ;not allowed - multiple T bit updates
Note that BMSET #$3,SR.H reads and writes the 32-bit SR register, while BMTSTC #$3,D0.L
affects only the T status bit in SR.
• Rule G.G.4 also applies to core vs. ISAP instructions in addition to ISAP vs. ISAP instructions. For
the latter case, the ISAP assembler is responsible for detecting the violation.
Rule G.G.4 Exceptions
• Two push or pop instructions that both implicitly write the SP register can be grouped in a VLES if
they access different, De (even) and Do (odd), register fields. For the following groupings, the
SC140 ensures that the SP register is written correctly. This case applies to the whole VLES.
Example 7-11 Dual Stack Pointer Destination Exception
push De field push Do field ;allowed
pushn De field pushn Do field ;allowed
pop De field pop Do field ;allowed
popn De field popn Do field ;allowed
ift push De field ifa push Do field ;allowed
• Two mutually exclusive writes to the same register (except the PC register) can be grouped in a
VLES.