Jaguar with slow running EFM32 microcontrollers

by Crossware 23. September 2011 21:14

If the Core clock of an Energy Micro EFM32 microcontroller is running slow, then it may be necessary for the operating frequency of Jaguar to be reduced.

To change the operating frequency of Jaguar, choose Project->Settings->Debug and select a Jaguar frequency divisor from the drop-down list.  Allowable divisors are 1, 2, 4, 8, 16 and 32.  The default when EFM32 firmware is installed is 1.

We experimented with the an EFM32G890 running from it's default 14MHz high speed internal RC clock and obtained the following results.

EFM Core Clock Divider     Required Jaguar Clock Divider
64 (220kHz)     32
32 (440kHz)     <=16
16 (880kHz)     <=8
8 (1.75MHz)     <=4
4 (3.5MHz)     <=2
2 (7MHz)     <=1
1 (14MHz)     <=1

If the EFM32 Core clock was divided by by 128, Jaguar was not able to run slow enough and so lost control.  In this situation, a mass erase may be required before Jaguar can take control again.

Keep in mind that the EFM32 high speed RC clock does not operate at a precise frequency and so our tests may not have been done at a base frequency of exactly 14MHz.

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