Hi, all
could you please help me to figure out how to wake up duo256m after power off without reconnecting the power source?
Are there some pins which must be shorted to wake up? From what I have understood from data sheet, there are none, but I’m not good at understanding schematics at all )
Assume the following scenario:
AFAIK, ARM or RISC-V cores in such an SoC either go deep sleep (wakeups are possible from low power cores — secondary or MCU), or stop. And in the second case you can’'t do a thing unless you power-cycle the whole system.
What you need, as I see it, is the first scenario: the first core goes to sleep until woken up by other cores or an interrupt.
Maybe you can do something with the 8051 core.
Thank you guys. Simple power on/off button seems to be a much longer story than I expected. I planned to utilize gpiokeys and busybox acpid for safe power off, but hoped that wake up could be not so complex
Hi, all
To continue the topic, I would like to share my experience in creating a hardware power-off button to safely shutdown Duo256m. There are a lot of such guides for Raspberry Pi, but as we do not have such luxury as prebuilt device tree overlays, all-in-one kernel, etc, it makes sense to describe how to achieve the same with Duo Buildroot SDK v2. I built RISCV version, but this is applicable for ARM, and original Duo
The outline of steps is as follows:
For step 1 select a pin and make sure it is configured as GPIO in duo-pinmux (pinmux | Milk-V ). Connect it to the one contact of the button, and other contact to the ground.
For step 2 we will utilize the gpio-keys feature (gpio-keys). First, we have to add our button to the device tree as a “device”. For this we have to add its definition to the root node in build/boards/cv181x/sg2002_milkv_duo256m_musl_riscv64_sd/dts_riscv/sg2002_milkv_duo256m_musl_riscv64_sd.dts ( path will be slightly different for other boards/platforms). Using this file is most straightforward but not the most elegant way to add a new device.
gpio-keys {
compatible = "gpio-keys";
power-button {
label = "power";
linux,code = <116>; // KEY_POWER
gpios = <&porte 4 GPIO_ACTIVE_LOW>;
wakeup-source;
};
};
Key codes are in dt-bindings/input/linux-event-codes.h. You have to lookup your pin GPIO bank and offset in Duo256M | Milk-V I use GP22, which belongs to porte and has offset 4.
Launch kernel menuconfig as described in Using a usb camera on milk-v Duos and select Device Drivers → Input Device Support → Keyboards → GPIO Buttons to buit in kernel [*] ( CONFIG_KEYBOARD_GPIO =y). Rebuild and flash firmware. If everything is ok, in dmesg there will be something like:
[ 1.207892] input: gpio-keys as /devices/platform/gpio-keys/input/input0
There will also be /dev/input/event0 device node.
To test the button, it makes sense also add evtest utility in buildroot configuration before build as described in Introduction | Milk-V
After reflashing, launch it and press the button a couple of times . If everything is set up properly, evtest will report key up/down events as below:
[root@milkv-duo]~# evtest /dev/input/event0
Input driver version is 1.0.1
Input device ID: bus 0x19 vendor 0x1 product 0x1 version 0x100
Input device name: "gpio-keys"
Supported events:
Event type 0 (EV_SYN)
Event type 1 (EV_KEY)
Event code 116 (KEY_POWER)
Properties:
Testing ... (interrupt to exit)
Event: time 1747244396.860994, type 1 (EV_KEY), code 116 (KEY_POWER), value 1
Event: time 1747244396.860994, -------------- SYN_REPORT ------------
Event: time 1747244397.138591, type 1 (EV_KEY), code 116 (KEY_POWER), value 0
Event: time 1747244397.138591, -------------- SYN_REPORT ------------
Event: time 1747244399.938112, type 1 (EV_KEY), code 116 (KEY_POWER), value 1
Event: time 1747244399.938112, -------------- SYN_REPORT ------------
Event: time 1747244400.164853, type 1 (EV_KEY), code 116 (KEY_POWER), value 0
Event: time 1747244400.164853, -------------- SYN_REPORT ------------
Now step 3 - handle key press to power off. Most common options are systemd-logind or acpid daemons. But 1) we do not have systemd-logind and definitely do not want it 2) we don’t have ACPI as well… There is acpid implementation in busybox, and before I’ve realized 2), I had built it as described in Introduction | Milk-V by including
CONFIG_ACPID=y
CONFIG_FEATURE_ACPID_COMPAT=y
In busybox.config. To my surprise, it is pretty able to detect key presses!
[root@milkv-duo]~# acpid -d
acpid: power
Now we have to configure acpid to execute the poweroff command at key press. There is a tutorial Power management - Alpine Linux for this. The last step is to launch acpid at system start-up. For this let’s create /etc/init.d/S03acpid script, using S49ntp as an example and make it executable. Now we have a fully working power-off button!
The last step to finalize the design would be creating an external circuit to safely disconnect the PSU after power off and re-apply power to turn the board on.
I wonder how critical it is to have a “safe poweroff” capability. I’ve been studying the CV1800 datasheet in preparation for some hardware work and I noticed that it has a rudimentary power warning capability - pin 30 “PWR_VBAT_DET” is described thus: “PWR_VBAT_DET is used to detect the status of the main power supply. If the voltage is low, the software will receive an interrupt first (such as stopping writing flash to prevent damage to the file system). If the voltage continues to drop, the RTC module will actively start the power-down program.”
I don’t know if the vendor’s Linux kernel supports this or not, but it seems like a fairly robust approach to preserving the integrity of the filesystem.
PWR_VBAT_DET appears to be early brown-out detection due to a low battery voltage. A sudden loss of power would probably not trigger the interrupt.
OP was asking how to power on. According to section 3.12.4.1 the RTC power domain is always on. Refer to RTC_EN_PWR_UP: power can be turned on with PWR_BUTTON1. Section 3.9.4.7:
Power off and power on
By configuring the req_shdn register to 1, the system software can put the chip into a power-off state (poweroff) including DDR. The RTC_EN_PWR_UP register can be configured to select the source that triggers the chip to power up and boot (powerup).
PWR_BUTTON1 looks to be pin 44 (ADC1) and is broken out to pin 32 of the Duo 64M. I suggest setting required registers and experimenting. I do not have the SG2002 datasheet detail to review differences for Duo 250M.
Hi, guys
The duo 256m schematic is here: duo-files/duo-256M/hardware/duo-256m-v1.01-schematic.pdf at main · milkv-duo/duo-files · GitHub
I definitely lack skills to fully understand it, but it seems that PWR_BUTTON1 is connected to PWR_GPIO[8] (sheet 7 in schema), which is not connected to any physical pin