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I and a co-worker are programming an 8051 uController in C. Last week we were struggling with a poor perfomance time of our program. So I talked to the assembly guy and we figured that our way of software timer handling was too slow. We were using 16 bit variables. Now I tweaked the timer software a bit and it runs about 4x faster, which is fast enough.
Digging a little deeper in the produced assembly code we found a 'persistent nuisance'. As a test I wrote these lines in code:
uint8 j; for(j=10;j--;){ rightTorqueArray[j] = j; }
The array is an unsigned char array but when we observe the assembly
MOV R7,#0AH ?C0001: MOV R6,AR7 DEC R7 MOV A,R6 JZ ?C0002 ; rightTorqueArray[j] = j; } ; SOURCE LINE # 52 MOV A,#LOW (rightTorqueArray) ADD A,R7 MOV DPL,A CLR A ADDC A,#HIGH (rightTorqueArray) MOV DPH,A MOV A,R7 MOVX @DPTR,A SJMP ?C0001 ?C0002:
We noticed that the array is adressed with LOW and HIGH so apparantly it is treated as a 16 bit variable. But my assembly-nese is not so well, so please correct me if I am wrong.
I set the Code Optimalization at level 8: reuse Common entry code and the emphasis at Favor speed.
The assembly was produced as a .SRC file using #pragma SRC on top of the C-file.