I have a custom board built around the nRF52840, which spends most of its life sleeping. I'm able to achieve ~3uA current draw when it is sleeping, but I've recently started running into corner cases where the current draw is much higher. I suspect that it is an issue with UART0.
As a specific example, if I disable UART0 and the other peripherals before going to sleep, I hit 3uA. However, if I transmit on the UART just before disabling it, I see ~620uA of current in sleep. Waiting on nrfx_uarte_tx_in_progress() and using delays does not seem to resolve the issue.
Here's a stripped down version of my code. The "printf("Going to sleep...\r\n");" is the offending line. If I comment that out, the sleep current is ok. Any idea how to fix this?
int main(void){ int32_t r; // Initialize HW peripherals r = HWC_UartInit(); if(r) SC_printf("HWC_UartInit: failed to initialize (%i)\r\n", r); printf("Going to sleep...\r\n"); // Uninitialize UART HWC_UartDeinit(); __SEV(); // Send an event (guarantees an event is set) __WFE(); // Will wake up immediately, clearing the event __WFE(); // This will put the device to sleep for realzies // Reinitialize the UART HWC_UartInit(); SC_printf("Awake again...\r\n"); while(1);}int32_t HWC_UartInit(){ nrfx_uarte_config_t uartConfig = NRFX_UARTE_DEFAULT_CONFIG; uartConfig.pseltxd = PIN_UART_TX; uartConfig.pselrxd = PIN_UART_RX; uartConfig.hwfc = NRF_UARTE_HWFC_DISABLED; uartConfig.parity = NRF_UARTE_PARITY_EXCLUDED; uartConfig.baudrate = NRF_UARTE_BAUDRATE_115200; nrfx_err_t e = nrfx_uarte_init(&uartInstance, &uartConfig, HWC_UartEventHandle); if(NRFX_SUCCESS==e) e = nrfx_uarte_rx(&uartInstance, &rxByte, 1); return NRFX_SUCCESS == e ? 0 : -1; }void HWC_UartDeinit(){ nrfx_uarte_rx_abort(&uartInstance); nrfx_uarte_uninit(&uartInstance); // Need to restart UARTE0 to reduce power. This may be related to an erratum. // devzone.nordicsemi.com/.../184882 *(volatile uint32_t *)0x40002FFC = 0; *(volatile uint32_t *)0x40002FFC; *(volatile uint32_t *)0x40002FFC = 1;}
