Siemens 80C517 and 80C537

The Siemens 80C517 and 80C537 provide high-speed 32-bit and 16-bit arithmetic operations as well as 8 data pointers which can be used for memory access. Using the high-speed arithmetic unit improves the performance of many int, long, and float operations.

The MOD517 control directive instructs the C51 compiler to generate code that utilizes the advanced features of these CPUs.

Data Pointers

The Siemens 80C517 and 80C537 provide 8 data pointers which can be used to improve memory accesses. Using multiple data pointers can improve the execution of library functions such as: memcpy, memmove, memcmp, strcpy, and strcmp. The 8 data pointers of the 80C517 and 80C537 can also reduce the stack load of interrupt functions.

C51 uses only 2 of the 8 data pointers of the 80C517 at a time. In order to keep the stack load in the interrupt routines low, C51 switches to 2 unused data

pointers when switching the register bank. In this case, the contents of the 5 register DPSEL are saved on the stack, and a new pair of data pointers is

selected. Saving the data pointers on the stack is no longer required.

If an interrupt routine does not switch to another register bank (for example, the function is declared without the using attribute), the data pointers must be saved on the stack (using 4 bytes of stack space). To keep the size of the stack as small as possible, use the MOD517(NODP8) directive to compile the interrupt routine and the functions called from within the interrupt. This generates code for the interrupt that uses only one data pointer and, therefore, only 2 bytes of stack space.

High-speed Arithmetic

C51 uses the 32-bit and 16-bit arithmetic operations of the 80C517 to improve performance of a number of math-intensive operations. C language programs execute considerably faster when using either of these CPUs.

The following tables show execution times for various arithmetic operations and compare the performance of the standard 8051 to that of the 80C517 CPU.

16-bit Binary Integer Operations

Times are shown in CPU cycles.

Floating-point Operations

Times are shown in CPU cycles.

NOTES

The execution times specified in the preceding tables do not take access times for variables or stack operations into consideration. Actual processing times may consume up to 100 additional cycles depending on the stack load and address space used.

When using the arithmetic features of the 80C517 and 80C537, note that operations involving the arithmetic processor are exclusive and may not be interrupted. Do not use the arithmetic extensions in both the main program and an interrupt service routine.

Use the following suggestions to help guarantee that only one thread of execution uses the arithmetic processor:

!Use the MOD517 directive to compile functions which are guaranteed to execute only in the main program or functions used by one interrupt service routine, but not both.

!Compile all remaining functions with the MOD517(NOAU) directive.

Library Routines