How to use Microchip AT91 power management modes
This page describes the way Microchip AT91 power management modes could be used in Linux.
The Microchip AT91 power management modes are
Standby - CPU switch to WFI
ULP0 - clocks are switch to low frequencies and CPU wakes on any interrupt
ULP1 - clocks are off and the number of CPU wake up sources is limited
Backup and Self-refresh (BSR) - CPU is shutdown and DDR memory is switch to self-refresh mode
The following table describes Linux Microchip AT91 power management modes supported by each individual Microchip AT91 SoC
|
|
| SoC |
Support modes |
| SAM9X60 |
standby |
| ULP0 |
| ULP1 |
| SAM9X7 |
standby |
| ULP0 |
| ULP1 |
| SAMA5D4 |
standby |
| ULP0 |
| SAMA5D3 |
standby |
| ULP0 |
| SAMA5D2 |
standby |
| ULP0 |
| ULP1 |
| BSR |
| SAMA7G5 |
standby |
| ULP0 |
| ULP1 |
| BSR |
|
|
|
The following table describes Linux Microchip AT91 power management modes supported by individual boards:
|
|
| Board |
Support modes |
| SAM9X60 Curiosity |
standby |
| ULP0 |
| ULP1 |
| SAM9X60-EK |
standby |
| ULP0 |
| ULP1 |
| SAMA5D4 Xplained |
standby |
| ULP0 |
| SAMA5D3 Xplained |
standby |
| ULP0 |
| SAMA5D2-ICP |
standby |
| ULP0 |
| ULP1 |
| BSR |
| SAMA5D27 WLSOM1 EK |
standby |
| ULP0 |
| ULP1 |
| BSR |
| SAMA5D27 SOM1 EK |
standby |
| ULP0 |
| ULP1 |
| SAMA5D2 PTC EK |
standby |
| ULP0 |
| ULP1 |
| SAMA5D2 Xplained |
standby |
| ULP0 |
| ULP1 |
| BSR |
| SAMA7G5-EK |
standby |
| ULP0 |
| ULP1 |
| BSR |
|
|
|
To be able to use
backup and self-refresh mode the
AT91Bootstrap has to be compiled with the following compilation flag:
CONFIG_BACKUP_MODE
The other power management modes could be used without special support in
AT91Bootstrap.
When switching to a low power mode Linux will use a Microchip AT91 power management modes if these modes were previously specified as kernel parameter from bootloader.
In Linux4sam reference distributions U-Boot is used as kernel bootloader. The Microchip AT91 power management modes are passed to kernel via
bootargs U-Boot variable in the format:
atmel.pm_modes=<standby-mode>,<suspend-mode>
The following table describes the value that could be provided in
atmel.pm_modes variable and it's effect when executing Linux specific power management commands.
|
|
| Mode |
Value |
Selected by Linux command |
Action while executing Linux power saving commands |
| standby-mode |
standby |
echo standby > /sys/power/state |
Switching to normal Linux standby mode |
| ulp0 |
Switching to Microchip AT91 ULP0 mode |
| ulp1 |
Switching to Microchip AT91 ULP1 mode |
| backup |
Switching to Microchip AT91 backup and self-refresh mode |
| suspend-mode |
standby |
echo mem > /sys/power/state |
Switching to normal Linux standby mode |
| ulp0 |
Switching to Microchip AT91 ULP0 mode |
| ulp1 |
Switching to Microchip AT91 ULP1 mode |
| backup |
Switching to Microchip AT91 backup and self-refresh mode |
|
|
|
In the booting process Microchip AT91 power management modes are mapped to standard Linux power management modes. Linux power management modes are called
standby and
suspend. To see how Microchip AT91 power management modes are mapped to Linux power management mode the following command could be executed after boot:
root@sama7g5ek-sd:~# dmesg | grep -i pm:
[ 0.050991] AT91: PM: standby: standby, suspend: ulp0
This means that Microchip AT91 standby mode is mapped to Linux standby mode and Microchip AT91 ULP0 mode is mapped to Linux suspend mode.
The following examples assume that user used
AT91Bootstrap and U-Boot bootloaders.
How to use ULP0 and BSR Microchip AT91 power management modes
To be able to use ULP0 and BSR Microchip AT91 power management modes the following settings has to be done:
1. Compile AT91Bootstrap with CONFIG_BACKUP_MODE flag
2. U-Boot bootargs variable has to contain: atmel.pm_modes=ulp0,backup
For instance, on SAMA5D2 Xplained board which boots form SD card, U-Boot
bootargs should look similar to this:
bootargs=console=ttyS0,115200 root=/dev/mmcblk0p2 rw rootfstype=ext4 rootwait atmel.pm_modes=ulp0,backup
To switch to
ULP0 mode from Linux execute the following command:
echo standby > /sys/power/state
To switch to
backup and self-refresh mode from Linux execute the following command:
echo mem > /sys/power/state
How to use ULP0 and ULP1 Microchip AT91 power management modes
To be able to use ULP0 and ULP1 Microchip AT91 power management modes the following settings has to be done:
1. U-Boot bootargs variable has to contain: atmel.pm_modes=ulp0,ulp1
For instance, on SAMA5D2 Xplained board which boots form SD card, U-Boot
bootargs should look similar to this:
bootargs=console=ttyS0,115200 root=/dev/mmcblk0p2 rw rootfstype=ext4 rootwait atmel.pm_modes=ulp0,ulp1
To switch to
ULP0 mode from Linux execute the following command:
echo standby > /sys/power/state
To switch to
ULP1 mode from Linux execute the following command:
echo mem > /sys/power/state
If, instead of using
echo standby > /sys/power/state to switch to ULP0 you want to use
echo mem > /sys/power/state and vice versa, the
atmel.pm_modes variable has to be in the format:
atmel.pm_modes=ulp1,ulp0
For instance, on SAMA5D2 Xplained board which boots form SD card, U-Boot
bootargs should look similar to this:
bootargs=console=ttyS0,115200 root=/dev/mmcblk0p2 rw rootfstype=ext4 rootwait atmel.pm_modes=ulp1,ulp0
How to use standard Linux power management modes
To be able to use standard Linux power management modes just don't place
atmel.pm_modes as part of U-Boot
bootargs variable
or specify
standby in
atme.pm_modes (something like
atmel.pm_modes=standby,ulp0)
For instance, on SAMA5D2 Xplained board which boots form SD card, U-Boot
bootargs should look similar to this:
bootargs=console=ttyS0,115200 root=/dev/mmcblk0p2 rw rootfstype=ext4 rootwait
This section will explain the wake up sources for SAMA5D2 Xplained board.
Wake up sources for ULP0 and standard Linux standby mode
ULP0 and normal Linux standby mode could use any interrupt to wake up from a power management mode. There are 2 ways of configuring wake up sources:
1. via /sys/devices/.../power/wakeup
2. via device tree
/sys/devices/.../power/wakeup
To configure a device to act as a wake up source for ULP0 and standard Linux standby mode just type
enabled or
disabled in power/wakup file specific to the device.
For instance, to configure PB1 button on SAMA5D2 Xplained board, to act as wake up source for ULP0 enter the following command on Linux:
echo enabled > /sys/devices/platform/gpio_keys/power/wakeup
Or, to disable it:
echo disabled > /sys/devices/platform/gpio_keys/power/wakeup
Device tree wake up
To configure a device to act as a wake up source for ULP0 and standard Linux standby mode just use "wakup-source" device tree propriety on the device itself in device tree.
For instance, to configure PB1 button on SAMA5D2 Xplained board, to act as wake up source for ULP0 the device tree bindings for PB2 button should look similar to this:
gpio_keys {
compatible = "gpio-keys";
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_key_gpio_default>;
bp1 {
label = "PB_USER";
gpios = <&pioA PIN_PB9 GPIO_ACTIVE_LOW>;
linux,code = <0x104>;
wakeup-source;
};
};
Wake up sources for ULP1 mode
In ULP1 wake up source are limited.
Linux4sam 6.0 kernel
In Linux4sam 6.0 wake up source for ULP1 could be configured via device tree.
For instance, to configure PB2 button and Ethernet to act as a wake up sources the device tree bindings for PMC should look similar to this:
pmc: pmc@f0014000 {
pmc_fast_restart {
compatible = "atmel,sama5d2-pmc-fast-startup";
#address-cells = <1>;
#size-cells = <0>;
wkpin: input@0 {
reg = <0>;
};
gmac_wol: input@10 {
reg = <10>;
atmel,wakeup-active-high;
};
};
};
For more information check
Fast startup for Ultra Low-Power (ULP) Mode 1
in SAMA5D2 datasheet
Vanilla kernel
In vanilla kernel ULP1 wake up sources could be configured via /sys/devices/.../power/wakeup files as explained above.
Wake up sources for backup and self-refresh mode
In backup and self refresh-mode wake up sources for SAMA5D2 Xplained boards are limited to PB2 button.
|
|
| Board |
BSR wakeup sources |
| SAMA5D2-ICP |
RTC |
| START button |
| SAMA5D27 WLSOM1 EK |
RTC |
| START SOM button |
| SAMA5D2 Xplained |
RTC |
| PB2 button |
| SAMA7G5-EK |
RTC |
| nSTART button |
|
|
|
For instance, to configure PB2 button on SAMA5D2 Xplained board to act as wake up source the device tree bindings for shutdown controller should look similar to this:
shdwc@f8048010 {
atmel,shdwc-debouncer = <976>;
input@0 {
reg = <0>;
atmel,wakeup-type = "low";
};
};
For ULP1 implementation in vanilla kernel, currently, there is no way to resume from
ACC or
RXLP events. For this reason the in Linux4sam 6.0 implementation is still based on device tree bindings.
--
Claudiu Beznea - 2018-10-17