During a debug session when the target device is running, the debugger usually only polls the target for its run/stopped state. The data polling service can make more use of this time by reading data sources on the target at a faster rate than can be achieved from the software frontend. On ARM-based devices as well as AVR UC3 devices, data can be read directly from memory during run mode, but on AVR 8-bit MCUs this data is transferred using the OCD Register, with the exception of AVR devices with UPDI, which can read some memory areas non-intrusively while in run mode. In addition, SAMD devices have two Debug Communication Channels (DCCn) available.
All polling functions are intended for use in RUN mode only. For AVR devices the polling service will be disabled when the device halts. When using the SAM polling modes however, the user must be sure to disable the service when the device halts.
The data polling service uses vendor command 'A' (0x8A).