A d v a nce d I n fo rm a t i o n

Eterna Datasheet

Linear Technology / Dust Networks

11

4.2

Serial Flash Emulation

When both RESETn and FLASH_P_ENn are asserted, Eterna disables normal operation and enters a mode to emulate the

operation of a serial flash. In this mode, its flash can be programmed with software updates. For details, see Section 2.10.

4.3

Operation

Once Eterna has completed startup, Eterna transitions to the Operational group of states (active / CPU active, active / CPU

inactive, and Doze). There, Eterna cycles between the various states, automatically selecting the lowest power state possible

while fulfilling the demands of network operation.

4.3.1

Active State

In Active state, Eterna’s relaxation oscillator is running and peripherals are enabled as needed. The ARM Cortex-M3 cycles

as needed between CPU-active and CPU-inactive (referred to in the ARM Cortex-M3 literature as “Sleep Now” or “Sleep on

Exit” modes). Eterna’s extensive use of DMA and intelligent peripherals that can independently move Eterna between the

Active and Doze states minimizes the time the CPU is active, significantly reducing Eterna’s energy consumption.

4.3.2

Doze State

The Doze state consumes orders of magnitude less current than the Active state (see Table 6) and is entered when all of the

peripherals, save the low power portion of the timer module, and the CPU are inactive. In the Doze state Eterna’s full state is

retained and Eterna is configured to detect, wake, and rapidly respond to activity on I/Os (such as UART signals and the

TIMEn pin). The Doze state also uses the 32.768-kHz oscillator and 32 kHz based timers are active.

4.4

Duty Cycling and Autonomous Peripherals

Eterna’s ability to quickly and efficiently transition between Doze and Active states, in conjunction with the ability of

peripherals to operate autonomously for most operations (shown in Figure 9), enables the system solution to significantly

reduce power consumption. For example the system can automatically go from Doze to Active and determine if RF energy is

present. The CPU is then only woken if a packet is detected, otherwise Eterna returns to Doze mode.

Figure 9

Low Energy Duty Cycling