I've got a custom-made board with Atmel SAM4S MCU on it. Currently this board doesn't have anything but MCU, decoupling capacitors, one LED on PA20 and a battery holder for powering up the MCU. Programming is occurring using SWD protocol via SWDIO/SWDCLK pins without any pullups. NRST is connected to a simple button that connects it to ground when pressed (according to the manual NRST doesn't require any external components). No crystals are used at all, MCU uses internal 4/8/12 RC oscillator and slow clock.
All works fine, I can access the MCU and it performs well.
But the problem is - I can't get it to consume less than ~400uA even in Backup mode. I've created a simple program that configures all PIOs as inputs with pull-ups (tried to configure them as outputs, with different combination of pull-ups,pull-downs,opendrain inputs/outputs, but it seems to consume the least amount of current when configured as input with pull-ups) and then immediately goes into backup mode without any wakeup source. I've googled everything, found several Atmel manuals about low power modes and they all recommend to configure SAM3/SAM4 ports as outputs with pull-down. But if I do that - MCU starts to consume ~4mA at 4MHz in backup mode agains ~0.7mA in Active mode at 4MHz.
Can anybody help me? What I might be doing wrong? I'm using ASF to configure all ports and I've configured MATRIX to use all ports as GPIO before going to sleep.
Discussion around product based on ARM Cortex M4 core.
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