Appendix 7 Precautions; Appendix 7.1 Precautions To Be Taken When Aligning Data - Renesas M32R-FPU Software Manual

APPENDIX 7
APPENDICES

Appendix 7 Precautions

Appendix 7 Precautions

Appendix 7.1 Precautions to be taken when aligning data

When aligning or allocating the data area following the code area in a program, the
alignment must be done from an address that has an adjusted word alignment.
If the data area is aligned or allocated without adjusting the word alignment, a 16-bit
instruction may exist in the high-order halfword of the word, and data with MSB of "1"
may be aligned to the following halfword. In this case, the M32R family upward-
compatible CPU recognizes the 16-bit instruction and the data as a pair of parallel
executable instructions and executes the instructions as such.
In consideration of the upward compatibility of software when programming, if the high-
order halfword has a 16-bit instruction, make sure that the following data area is aligned
or allocated from an address that has an adjusted word alignment.
1 word
+0 +1 +2 +3
MSB MSB
0 1
16-bit instruction data
data
APPENDICES-29
M32R-FPU Software Manual (Rev.1.01)