C51: Dual Data Pointer Performance Increase

Information in this article applies to:

• C51 Version 5.50 and later

QUESTION

How are the dual data pointers of the several 8051 derivatives used by the C compiler? What is the performance advantage?

ANSWER

In C51, only the library routines use the dual data pointers. The dual data pointers are not used by the C compiler to optimize your program code.

The following library routines use dual data pointers when copying or comparing 2 memory blocks:

• memmove
• memcpy
• memcmp
• strcpy
• strcmp

There is a distinct performance advantage in using dual data pointers. As an example, we profiled the memcpy function. This function shows the best performance increase you can expect. The following table gives the performance increase by using dual data pointers on the Dallas Semiconductor 320. This is compared to the same speed 8051 CPU with only 1 data pointer.

memcpy 1 Byte         2.4x
memcpy 10 Bytes       3.3x
memcpy 100 Bytes      3.8x
memcpy 1000 Bytes     3.9x

Note that the Dallas part already runs 3 times faster than a standard 8051.

SEE ALSO

• C51: Dual Data Pointers for DALLAS Parts
• C51: Dual Data Pointer and Philips
• C51: CORRUPTION OF DPTR WHEN USING MODP2
• MON51: Doesn't Save the Dual Data Pointers
• C51: ?C?COPYXX UNRESOLVED EXTERNAL FROM EVAL VERSION

Last Reviewed: Thursday, February 25, 2021