What is a soft switch? Soft switches are relative to hard switches. Hard switches, as the name suggests, the power supply is completely dependent on the hardware, is the opening and closing of the physical layer; and the soft switch must be closed by means of software, specifically by software. Both have their own advantages and disadvantages.
Because the former is the operation of the physical layer, it can be said that the power supply and the system part are completely blocked, so the leakage current is very small when the shutdown is closed, but the defect is that the software cannot give any notification information when it is closed; the latter is only the level operation, and cannot be closed after the shutdown. The power supply is partially isolated from the system, so the leakage current is relatively large, but the advantage is that the shutdown is controlled by software, so you can prepare accordingly before shutting down. Because of this characteristic, electronic devices have very few designs with hard switches, and more are soft switches. To give a simple example, our common home computer is a soft switch design. Imagine joining a computer with a hard-switch design. What will be the result?
The result is estimated to be the same as when we used the computer and suddenly unplugged the plug. In this way, the damage caused by the computer equipment, especially the hard disk, is immeasurable.
Soft switch design hardware articlesFor the soft switch, at the moment we press, because there is no power to the CPU, there is no possibility of program execution, so the operation of "open" can only be done in hardware. When the system is running, the software is now operational and we can shut down the device by operating the GPIO. In summary, if we want to implement soft switching, we must have two GPIO ports. One is DETECT_KEY, which is used as an input to detect whether the button is pressed; the other is GPIO_SHDW, which is used as an output to control the closing of the power supply.
Now, let's look at a typical soft-switching circuit (Figure 1, the following explanation is referred to by the label of the circuit diagram):
The circuit is very simple, there are four external nodes, as follows:
PWR_ON: Used to control the power of the system. When it is high, the system supplies power normally.
VDD33D: Directly connected to 3.3V
GPIO_SHDW: Turn off system power when it is low
DETECT_KEY: Detects the state of button S1.
We now analyze the circuit step by step according to the process from boot to shutdown:
1. Not turned on, S1 is not pressed.
At this time, GPIO_SHDN is low, and the control pins (PIN1) of Q1 and Q2 are directly controlled, so that the voltage of VDD33D cannot be output to the POW_ON terminal. While D1 is not pressed, the diode is also in a blocking state, and VDD33D at the S1 terminal cannot be delivered to the POW_ON terminal. Therefore, the entire system is still closed.
2.S1 press and turn on.
When S1 is pressed, diode D1 is turned on, and the voltage of VDD33D at the S1 terminal is sent to the PWR_ON terminal, and the system starts to start. Set GPIO_SHDN high when the system starts up. At this time, PWR_ON has input R2, VDD33D voltage at R3 terminal, and the voltage on both sides of D1 is basically in equilibrium state, D1 is equivalent to disconnection, and the voltage at S1 terminal cannot be loaded to PWR_ON.
3. S1 is released and the system is running normally.
When S1 is released, D1 can no longer be turned on. At this time, the voltage has been mainly input from VDD3D of R2 and R3, so that PWR_ON is always in the high state, so the system is always in normal operation.
4.S1 is pressed and the system is running normally.
Because S1 is pressed, Q3 is turned on, pulling down the voltage under the R6 terminal. At this time, the DETECT_KEY GPIO port detects that the level is low, and the software starts to enter the timing state.
5.S1 is released.
Because S1 has been released, Q3 is no longer turned on, the voltage at the lower end of R6 is restored, and DETECT_KEY detects the level as high. At this point, the software compares with the threshold. If the predetermined threshold is exceeded, the system is shut down; otherwise, this operation is ignored. The reason why it is compared with the threshold here is the need for anti-shake. Because in actual use, there may be a slight extremely short voltage drop at the R6 end. If the software does not set a threshold, it will be turned off when it is detected, which is not allowed for the product.
Soft switch design software articlesCompared to the hardware, the soft switch software code is simpler, just need to detect DETECT_KEY. The implementation of this function is mainly through GPIO, and wince does not define the upper level of GPIO, and the operation mode of each CPU GPIO is different, so this article can not give a complete usable code, only pseudo code can be used as an example. explain. Although it is pseudo code, it still has some meaning for understanding its process.
Void Power_On()
{
...
/ / Set GPIO_SHDN to high
SetGPIO_HIGH(GPIO_SHDN);
...
}
DWORD PWR_IntrThread(PVOID pParam)
{
....
/ / Enable interrupt
EnableInterrupt();
/ / Initialize interrupt
InterruptInitialize(btnSysIntr, hNotifyEvent, 0, 0)
While(TRUE)
{
/ / Wait for the interrupt event
dwRet = WaitForSingleObject(hNotifyEvent, INFINITE);
If(dwRet == WAIT_OBJECT_0)
{
/ / Interrupt processing is completed, let the interrupt enter the processing again
InterruptDone(btnSysIntr);
/ / Wait for the interrupt processing event again
dwRet = WaitForSingleObject(hNotifyEvent, 1000);
If(dwRet == WAIT_TIMEOUT)
{
/ / When its bit WAIT_TIMEOUT, it means long press, enter the poweroff function
EnterPowerOff();
}
}
}
....
}
Void EnterPowerOff()
{
...
While(TRUE)
{
If(IsGPIOHigh(GPIO_DETECT_KEY) != FALSE)
{
//S1 has been released, jumping out of the loop
Break;
}
}
/ / Turn off the system power
SetGPIO_LOW(GPIO_SHDN);
...
}
The only thing to note here is the EnterPowerOff function, where you must check if S1 has been released. If S1 has not been released, GPIO_SHDN is set to LOW. Since the VDD33D voltage is input to the PWR_ON terminal at the S1 terminal, the system cannot be turned off.
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