Position2Go Review 4. Structure

freebsder

Position2Go Review 4. Structure [Copy link]

 

This section attempts to describe the structure of P2G hardware and software at a certain level.

Regarding the hardware composition and a rough introduction of Position2Go, the official provides two Application Notes: "P2G_Application_Note" (AN553) and "P2G_Software_User_Manual".

Although the official documents above are provided, Position2Go is a radar processing module with a classic structure, which allows us to observe the system from a higher level of abstraction of software and hardware: how the actual software and hardware structure achieves the radar system. The next evaluation plan is to observe the system from a higher level of abstraction, namely the algorithm.

The hardware block diagram of P2G is shown below. The baseband signal, intermediate frequency signal, radio frequency signal, local oscillation, filtering, synthesis, amplification and other components on the module are commonly found in various communication components. It is a signal processing system with a classic architecture.

The following figure shows an abstract block diagram of an FMCW radar:

Putting aside the complexity of the actual system, the principle of radar is not complicated at the abstract level. From the block diagram model to the actual system, the waveform generator of the baseband signal is completed by LMX2491 in the P2G module; the filtering and amplification part of the intermediate frequency signal at the receiving end is composed of two-stage amplifiers OPA2376 and PGA112, of which PGA112 is a gain-adjustable amplifier; AD sampling and signal processing are handled by XMC4700 MCU; the rest of the parts such as VCO, mixing, power amplification, local oscillator buffer, etc. are all processed by Infineon BGT24MTR12; all functional devices are controlled by XMC4700 MCU as a whole to form an actual radar.

The triangular wave modulation signal generated by LMX2491 is controlled by the VCO in BGT24MTR12 to generate a frequency modulated continuous wave with a triangular wave frequency change in time. One part is transmitted through the TX antenna after being amplified by the internal power of BGT24MTR12, and the other part is used as the local oscillator signal. After the electromagnetic wave encounters the target, part of the electromagnetic wave is reflected back to the radar according to the reflection cross-section property of the object and received by the RX receiving antenna. P2G has two RX receiving antennas, and the target angle is calculated based on the known antenna spacing. Radars for more professional application scenarios will form a radar array according to certain requirements to meet the directional analysis adapted to the needs. The local oscillator signal and the echo signal change in frequency or phase, and the intermediate frequency beat signal is obtained after mixing inside the BGT24MTR12. The beat signal reflects the distance and moving speed of the target in frequency and phase. The intermediate frequency signal is amplified by OPA2376 and PGA112 and then collected by the ADC component of XMC4700 to form a set of sampled data. Then, the DSP component in XMC4700 performs FFT transformation on this set of data to reflect the distance, speed, angle and other information of the measured target. Finally, it interacts with the outside world through the USB/USART and other components of XMC4700.

The above describes the abstract observation of the radar system from the functional devices of the distributed structure on the P2G reference board.

Next, we will describe the system from the perspective of the structure of the XMC4700 control function. The purpose of this is to describe the observation that components + organization = system.

The functional components of XMC4700 are as follows: ADC, GPIO, TIMER (CCU), DMA, USB, SPI listed in the figure below and ERU, DSP not listed.

SPI is used to control LMX2491, BGT24MTR12 and PGA112. For example, to set the frequency bandwidth, frequency ramp time, waveform, magnification, etc., you can refer to the C file configuration examples of the relevant devices in the DAVE project.

ADC+DMA is used to sample the intermediate frequency signal. For specific sampling settings, please refer to the process of adding APP support to the DAVE project of P2G_FMCW and view the configuration graphically.

The CCU clock unit is used to accurately control the sampling process. When you see the algorithm later, you will naturally understand the actual situation of this process. The GPIO input and output are also used to detect and set the system status, such as getting the rise of the modulation signal from the LMX2491. DSP is very direct, signal processing, and I will talk about other things when I see the algorithm later.

Finally, it is important to note that the special functional component of XMC4700 is ERU, namely event request unit. It can be said that the key to the control part of the entire P2G system lies in the use of ERU. ERU specializes the request service process into the sequence of request generation, request processing and routing, and request service, which is the application framework of ERU:

Events can be generated by ADC, CAPCOM, GPIO, DAC, POSIF, etc. ERU processes these event requests comprehensively, such as the combination of multiple request events, signal determination triggering, triggering peripheral cross matrix, response gating, etc., and finally generates pulse or level output to trigger ADC, CAPCOM, IRQ, DSD, POSIF and other peripherals to perform corresponding services for the request. To a certain extent, we can regard the ERU unit as a small FPGA.

Some MCU devices from other manufacturers also have similar functional components, such as cross-ports, etc. Most of the restrictions on these cross-ports are provided in the form of hard-wired configurations, and some MCU devices from other manufacturers cannot map the requests generated by the cross-ports to multiple services simultaneously. Infineon's ERU is undoubtedly very powerful.

The main control process is driven by the PLL_TRIG1 output of LMX2491 in the system: PLL_TRIG1 outputs the state of the modulation signal, which is routed to the CCU timer through the ERU for synchronous sampling of the 4-way ADC. The sampling time of the CCU timer is determined by the bandwidth, ramp time, and number of continuous frames of the continuous chirp signal. These parameters will be clear in the following algorithm, so they will not take up much space here. The data obtained from the 4-way sampling is collected and saved in the SRAM of the XMC4700 through DMA. The subsequent process can be imagined. The data is processed by DSP digital signal according to the algorithm to finally obtain the distance, speed and angle information.

This content is originally created by EEWORLD forum user freebsder. If you want to reprint or use it for commercial purposes, you must obtain the author's consent and indicate the source