An embedded system is a specialized computer system that is part of a device or device. Typically, an embedded system is an embedded processor control board in which the control program is stored in ROM. In fact, all devices with digital interfaces, such as watches, microwave ovens, video recorders, and automobiles, use embedded systems. Some embedded systems also include an operating system, but most embedded systems implement full control from a single program. logic.
An embedded system device generally consists of an embedded computer system and an execution device. The embedded computer system is the core of the entire embedded system, and is composed of a hardware layer, an intermediate layer, a system software layer, and an application software layer. The execution device, also known as the controlled object, can accept control commands issued by the embedded computer system to perform the specified operations or tasks. The actuator can be very simple, such as a tiny motor on the phone, which is turned on when the phone is in vibration receiving state; it can also be complicated, such as the SONY smart robot dog, which integrates multiple micro-small control motors and various sensors. Thereby, various complicated actions and various state information can be performed.
Defined from the application object, the embedded system is a combination of software and hardware, and can also cover auxiliary devices such as machinery. The embedded system generally recognized in China is defined as: application-centered, computer-based, software and hardware tailored to meet the strict requirements of the application system for functions, reliability, cost, size, power consumption and other special computer systems.
1, small external bus such as single chip
Small MCUs such as single-chip microcomputers generally have an external bus, which can be used to connect a true color LCD (asynchronous bus interface TFT display). Most of the phones use a screen that synchronizes (first give an address, then continuously brush the data) interface.
2, ARM processor application scenarios
ARM7: industrial control, mobile phone;
ARM9: image display;
Cortex-A: High-performance applications: mobile phones, cottages;
Cortex-M: low-end applications;
Cortex-R: mid-range applications are relatively rare;
3, ARM processor exception
In general, some of the previous interrupts (such as the first 15) are designed by ARM itself and are fixed. The middle part of the latter part is defined by different chip manufacturers.
4, the processor's System Timer
The System Timer, Systick, can be used as a general-purpose timer when there is no OS. When the OS is required, it can be used as the system clock of the OS.
5. The same interrupt is disabled and enabled by different registers.
At present, there are many phenomena in the processing, and the prohibition and enable of the same interrupt are controlled by different registers. When the interrupt is disabled, write 1 to the corresponding bit in the interrupt mask register. When the interrupt is enabled, write 1 to the corresponding bit in the interrupt enable register.
The benefits of this separate control are:
A. It is not necessary to read out the value of the interrupt control register first, and then write back after performing the OR operation;
B. Write 1 directly, it will not affect the interrupt controlled by other bits;
6, OD gate output
Can be used when the processor level does not match the peripheral level.
7, how to set the state of IO to reduce power consumption
If an input pin is left floating, there is leakage current, which will consume power. Judgment method: When you touch it by hand, the current will change.
A. Set the unused pins to the output mode of 0 or 1;
B. If configured as an input pin, the internal pull-up should be turned on;
8, ADC and DAC
The ADC and DAC should be turned off while the system is sleeping, otherwise power will be consumed.
9, the use of watchdog
A. Don't feed the dog in the interruption;
B. The more regular the dog is, the better;
10, I2C bus
Both SDA and SCL are bidirectional, open-drain driven, and must be pulled with a pull-up resistor.
I2C protocol communication process:
A. Send start signal (who sends the start signal, who is the host)
B. Send the slave address
C. Transferring data
D. Send stop signal
The I2C bus emulated by software has the following disadvantages:
A. Cannot perform bus arbitration
B. It is difficult to implement the slave device because the clock signal is always detected;
11, logic 0 page
The logic 0 pages of many MCUs can be arbitrarily mapped so that multiple systems can be programmed in flash. The configuration can be implemented by configuring the byte configuration system to boot from a different address.
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