A dedicated computer system, embedded design and development analysis

What is an embedded system? What should be paid attention to in its design and development? An embedded system is a dedicated computer system as a part of a device or equipment. Typically, an embedded system is an embedded processor control board with a control program stored in ROM. In fact, all devices with digital interfaces, such as watches, microwave ovens, video recorders, cars, etc., use embedded systems. Some embedded systems also contain operating systems, but most embedded systems are controlled entirely by 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 consists of a hardware layer, an intermediate layer, a system software layer and an application software layer. The execution device is also called the controlled object. It can accept the control commands issued by the embedded computer system and perform the specified operations or tasks. The execution device can be very simple, such as a tiny motor on a mobile phone, which is turned on when the phone is in the vibration receiving state; it can also be very complex, such as a SONY smart robot dog, which integrates multiple micro-control motors and various sensors. This allows you to perform various complex actions and experience various status information.

Defined from the perspective of application objects, embedded systems are a combination of software and hardware, and can also cover attachments such as machinery. The definition of embedded system generally recognized in China is: a special computer system that is application-centered, based on computer technology, and whose software and hardware can be tailored to meet the strict requirements of application systems such as function, reliability, cost, volume, and power consumption. Let us summarize 11 common problems in embedded design and development.

1. Small external buses such as microcontrollers

Small MCUs such as microcontrollers generally have external buses that can be used to connect true color LCDs (asynchronous bus interface TFT displays). On mobile phones, most of them use the synchronization (first give an address, and then continuously refresh the data) screen interface.

2. Application scenarios of ARM processors

ARM7: industrial control, mobile phones;

ARM9: image display;

Cortex-A: high-performance applications: mobile phones, copycat laptops;

Cortex-M: low-end applications;

Cortex-R: mid-range applications, relatively rare;

3. Abnormalities of ARM processor

Under normal circumstances, some of the first interrupts (such as the first 15) are designed by ARM itself and are fixed, while some of the later mid-range interrupts are defined by different chip manufacturers.

4. System Timer of the processor

System Timer is Systick, which can be used as a general timer when there is no OS. When the OS is needed, it can be used as the system clock of the OS.

5. The disabling and enabling of the same interrupt are controlled by different registers.

At present, this phenomenon occurs in many processes. The disabling and enabling of the same interrupt are controlled by different registers. When disabling the interrupt, write 1 to the corresponding bit in the interrupt mask register. When enabling the interrupt, write 1 to the corresponding bit in the interrupt enable register.

The advantages of such separate control are:

A. There is no need to read the value of the interrupt control register first, perform an OR operation and then write it back;

B. Directly writing 1 will not affect the interrupts 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 status of IO to reduce power consumption

If an input pin is left floating, there will be leakage current and power consumption. Judgment method: When you touch it with your hands, the current will change.

A. Set unused pins to 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

When the system is sleeping, the ADC and DAC should be turned off, otherwise power will be consumed.

9. Use of watchdog

A. Don’t feed the dog during interruption;

B. The less regular you feed your dog, the better;

10. I2C bus

SDA and SCL are both bidirectional and open-drain driven, and a pull-up resistor must be added when using them.

Communication process of I2C protocol:

A. Send the start signal (whoever sends the start signal is the host)

B. Send from address

C.Transfer data

D.Send stop signal

The I2C bus simulated by software has the following disadvantages:

A. Bus arbitration cannot be performed

B. Since the clock signal must be detected all the time, it is difficult to implement a slave device;

11. Logical 0 page

The logical 0 page of many MCUs can be mapped arbitrarily, so that multiple systems can be programmed in flash. Configuring the system to boot from a different address via configuration bytes allows for upgrades. The above are some precautions for the design and development of embedded systems. I hope they can help you.