User manual

Atmel-ICE [USER GUIDE]

42330A-MCU-07/2014

9. Special Considerations

9.1 Atmel AVR XMEGA OCD

OCD and clocking

When the MCU enters stopped mode, the OCD clock is used as MCU clock. The OCD clock is either the JTAG

TCK if the JTAG interface is being used, or the PDI_CLK if the PDI interface is being used.

I/O modules in stopped mode

In contrast to earlier Atmel megaAVR devices, in XMEGA the I/O modules are stopped in stop mode. This

means that USART transmissions will be interrupted, timers (and PWM) will be stopped.

Hardware breakpoints

There are four hardware breakpoint comparators - two address comparators and two value comparators. They

have certain restrictions:

● All breakpoints must be of the same type (program or data)

● All data breakpoints must be in the same memory area (IO, SRAM or XRAM)

● There can only be one breakpoint if address range is used

Here are the different combinations that can be set:

● Two single data or program address breakpoints

● One data or program address range breakpoint

● Two single data address breakpoints with single value compare

● One data breakpoint with address range, value range or both

Atmel Studio will tell you if the breakpoint can't be set, and why. Data breakpoints have priority over program

breakpoints, if software breakpoints are available.

External reset and PDI physical

The PDI physical interface uses the reset line as clock. While debugging, the reset pullup should be 10k

or more or be removed. Any reset capacitors should be removed. Other external reset sources should be

disconnected.

Debugging with sleep for ATxmegaA1 rev H and earlier

There was a bug in the early versions of the ATxmegaA1 family that prevented the OCD to be enabled while

the device was in certain sleep modes. There are two methods to use to get back on the debugging:

● Go into the Atmel-ICE Options in the Tools menu and enable "Always activate external reset when

reprogramming device"

● Perform a chip erase

The sleep modes that trigger this bug are:

● Power-down

● Power-save

● Standby

● Extended standby

9.2 Atmel megaAVR OCD and debugWIRE OCD

IO Peripherals

Most I/O peripherals will continue to run even though the program execution is stopped by a breakpoint.

Example: If a breakpoint is reached during a UART transmission, the transmission will be completed and