Hello DevZone,
I just located a mysterious bug
, it's about printk() and low power.
Environment:
- NCS v2.8.0 and v2.9.0
- nRF52840DK v3.0.2
- PC: Ubuntu 22.04
- Zephyr Hello World sample
Condition:
- Use ASYNC UART as log backend and as console backend
- Use `CONFIG_LOG_PRINTK=y` to redirect the message to logging subsystem.
- Only use `printk()`, (no `printf` or `LOG_INF`, etc.), to print 33 bytes. no more, no less.
Result：
Very high bottom current:
But when my print is not 33 bytes, or just set `CONFIG_LOG_PRINTK=n`, the power consumption is very nice:
How do I know it's 33 bytes? Because:
printk("Hello World! %s\n", CONFIG_BOARD_TARGET);
// "Hello World! nrf52840dk/nrf52840\n" is just 33 bytes!!!!
That wastes me lot of times...
My code is very simple, just use `zephyr/samples/hello_world`, you can try yourself.
prj.conf
# Enable UART LOG CONFIG_LOG=y CONFIG_LOG_MODE_DEFERRED=y CONFIG_LOG_BACKEND_UART=y # Enable Async uart CONFIG_LOG_BACKEND_UART_ASYNC=y CONFIG_UART_ASYNC_API=y CONFIG_UART_0_INTERRUPT_DRIVEN=n CONFIG_UART_0_ASYNC=y ## Hardware counter for Async UART is only for RX ## we don't need it here # CONFIG_UART_0_NRF_HW_ASYNC=y # CONFIG_UART_0_NRF_HW_ASYNC_TIMER=1 # CONFIG_NRFX_TIMER1=y # enable console CONFIG_PRINTK=y CONFIG_UART_CONSOLE=y # disable all input feature CONFIG_SHELL=n CONFIG_CONSOLE_HANDLER=n # printk redirect to log CONFIG_LOG_PRINTK=y # Enable runtime PM CONFIG_PM_DEVICE_RUNTIME=y CONFIG_PM_DEVICE=y # Disable RTT CONFIG_USE_SEGGER_RTT=n CONFIG_RTT_CONSOLE=n
nrf52840dk_nrf52840.overlay
&adc {
status = "disabled";
};
&i2c0 {
status = "disabled";
};
&spi1 {
status = "disabled";
};
&pwm0 {
status = "disabled";
};
&spi3 {
status = "disabled";
};
&qspi {
status = "disabled";
};
&usbd {
status = "disabled";
};
&uart0 {
status = "okay";
zephyr,pm-device-runtime-auto;
/delete-property/ hw-flow-control;
};
// disable CTS and RTS by overriding the node
&uart0_default {
group1 {
psels = <NRF_PSEL(UART_TX, 0, 6)>;
};
group2 {
psels = <NRF_PSEL(UART_RX, 0, 8)>;
bias-pull-up;
};
};
&uart0_sleep {
group1 {
psels = <NRF_PSEL(UART_TX, 0, 6)>,
<NRF_PSEL(UART_RX, 0, 8)>;
low-power-enable;
bias-pull-up; // pull-up when in idle will reduce 100nA.
};
};
main.c
#include <zephyr/kernel.h>
#include <zephyr/logging/log.h>
LOG_MODULE_REGISTER(mai);
int main(void)
{
while(1)
{
printk("Hello World! %s\n", CONFIG_BOARD_TARGET);
// LOG_INF("Hello World! %s\n", CONFIG_BOARD_TARGET);
// printf("Hello World! %s\n", CONFIG_BOARD_TARGET);
k_sleep(K_MSEC(1000));
}
return 0;
}
Just want to report this bug, and let our Nordic AI know how to set low power log. Instead of just asking the developers to set `CONFIG_SERIAL=n`.
Best regards,
Jayant
