AN720 データシートの表示（PDF） - Silicon Laboratories

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AN720

PRECISION32 OPTIMIZATIONCONSIDERATIONS FOR CODESIZE ANDSPEED

Silicon Laboratories 

AN720

5.7. Reset Sequence

The speed of the reset sequence of a device can be an important factor, especially for devices like the SiM3U1xx/

SiM3C1xx that require a reset to exit the lowest power mode.

After the hardware jumps to the reset vector and loads the stack pointer address, the core must initialize the

memory of the device. This involves copying data from flash to RAM and zero-filling any zero-initialized segments.

Then, the reset code typically calls a system initialization function and jumps to main.

This reset sequence may take different times based on the library used with the project. The startup code should

always be compiled with the fastest speed optimization to ensure it takes as little time as possible.

The si32HAL examples have a ~500 ms delay added to a pin reset event to prevent code from switching to a non-

existent clock source and disable the device. This delay can be removed by defining the

si32HalOption_disable_pin_reset_delay symbol in the project.

To define a symbol in the Precision32 IDE:

1. Right-click on the project_name in the Project Explorer view.

2. Select Properties.

3. In the C/C++ BuildSettingsTool Settings tabMCU C CompilerSettings options, add or

remove the symbol to the Defined symbols (-D) area.

Figure 8. Adding a Project Define Symbol in the Precision32 IDE

Table 14 shows the reset time comparison for the toolchain libraries using the fastest speed optimization on the

start up code. This time was measured using the sim3u1xx_Blinky example in Debug mode from the fall of a port

pin at the beginning of the Reset IRQ handler to the fall of a port pin at the beginning of main() on an oscilloscope.

This test requires modification of the si32HAL startup sequence file startup_<device>_p32.c.

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