AN1278 datasheet(37/44 Pages) STMICROELECTRONICS

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LIN (LOCAL INTERCONNECT NETWORK) SOLUTIONS

sponding software performance is different. Table 9 and Table 10 give performance summa-

ries for both examples.

Table 9. ST72254 Example performance summary

Table 10. ST72334 Example performance summary

4.4.1 Timing considerations

The runtime performance of the software depends on many parameters like the memory

model, the compiler options and the compiler version and also on the application (lin_ai.c is

part of the LIN interrupt). As a result it is impossible to give generally applicable software

runtime performance data.

A first timing consideration is the maximum reachable speed running the software without any

application software. In this case only the software emulating the SCI communication

(ST72254 example) has speed limitations. In the above ST72254 example the maximum

speed reachable was 16kbaud. The software using the on-chip SCI peripheral has no LIN

speed limitation.

Then if you add some application code in the lin_ai.c file, you make the LIN interrupt service

routine longer and therefore decrease the software performance. That’s why in order to

achieve better performance you should keep actions done in the lin_ai.c file as short as pos-

sible. Nevertheless the software that uses the on-chip SCI peripheral should not be speed lim-

ited under 20kbaud.

The final timing consideration is when the application software needs to interrupt the LIN com-

munication. The LIN software is interrupt-driven and between two interrupts the application

software can run some other code. As long as the application software is interruptable, the LIN

software will interrupt it when needed. Problems can occur if the application software is not in-

Compiler version

v4.3a

Memory model

+modm - memory short

Compiler options

+debug

Code size

whole project

2.1 kbyte

lin.o

1.8 kbyte

lin_ai.o

44 byte

LIN interrupt - CPU load

17%

Max LIN baudrate @16MHz

16kbaud

Compiler version

v4.3a

Memory model

+modms - memory small

Compiler options

+debug

Code size

whole project

1.4 kbyte

lin.o

1.0 kbyte

lin_ai.o

44 byte

LIN interrupt - CPU load

Max LIN baudrate @16MHz

no limit-20kbaud

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