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On the Apollo2 series devices from Ambiq Micro, SWO is supported. However, a few device specifics apply which are described in the following.

Clock source

For most devices, the SWO clock is derived from the current MCU clock. This is not the case for the Apollo2 series devices. On these devices, the SWO clock is derived from the internal 48 MHz High Frequency RC Oscillator (HFRC).

The SWO clock provided to the CoreSight SWO/trace units is not 1:1 the speed of the HFRC, but can be configured via the Apollo2 device specific register MCUCTRL.TPIUCTRL[CLKSEL]

CLKSEL meaning
Value Meaning
1 SWOClock == HFRC / 2
2 SWOClock == HFRC / 8
3 SWOClock == HFRC / 16
4 SWOClock == HFRC / 32

Note: J-Link handles the current setting of this register automatically when calculating the SWO speed to be used.

Note: When selecting the CPU frequency in IDEs for J-Link SWO usage, select 48 MHz for the Ambiq Apollo2 series devices.

SWO pin

On the Apollo2 series devices, multiple pins are capable of being configured as SWO:

  • PAD15
  • PAD22
  • PAD24
  • PAD30
  • PAD33
  • PAD41
  • PAD45
  • PAD46

Note: All J-Link default configurations configure and use PAD41 as SWO because this is the PAD used on the EVBs from Ambiq.

Sample projects

Sample projects that demonstrate SWO usage are available for the following eval boards: