Sharing practical experience in FPGA system design Sharing practical experience in FPGA system design

This post mainly introduces some problems and solutions we encountered in the process of FPGA hardware system design. You are also welcome to participate in the discussion. It mainly involves the following aspects:
1. Chip selection Including the selection principles of FPGA chips, peripheral chips such as memory, power supply, interface chips, etc. We will recommend some chips with good performance, low price and easy to buy, saving you time to search for chips.
2. Schematic design skills Including how to be compatible with different types of FPGAs, ensuring the upgrade space of system design, etc.
3. Basic principles of PCB design For general FPGA systems, as long as these basic principles are guaranteed, you don’t have to learn those complicated simulation software and high-speed PCB design knowledge, and you can still design a stable and reliable hardware circuit board.
4. Circuit debugging skills How to debug a circuit board that has just been soldered, especially for friends who are debugging a circuit board for the first time, it will definitely be helpful.
================Part 1: Suggestions
on chip selection === ... If you need to go to market as soon as possible and seize the market, you generally choose to develop simple Altera or Xilinx products; B. If the product is already stable and you need to improve confidentiality and stability, you can consider Lattice, QuickLogic or Actel's anti-fuse type or Flash type FPGA; C. If you need strong anti-interference performance and the working environment is very harsh, such as aerospace, you generally choose Actel's products. Introduction to FPGAs of several manufacturers: Altera's chips are widely used in domestic universities, just like there are many people using VHDL in universities. Altera's chip products are relatively complete. Currently, the main ones are Flex10K series, ACEX1k series, Cyclone series, etc., which are widely used. Stratix series are generally used more in high-end fields such as communications. Flex10K is a relatively old series with a high price. It is a 5V device and is mainly used in 5V signal environment. It has better anti-interference performance, but its power consumption and volume are relatively large, and its scale is also limited. ACEX1K is a relatively successful series, compatible with 5V and 3.3V. If the system is a mixed signal system of 3.3V and 5V, and there are many 5V signals, it is recommended to use the ACEX1K series, which is also good in price. However, the largest scale is 100,000 gates, and there is little room for upgrade. The Cyclone series is currently the lowest-cost FPGA of Altera, but it can only support 3.3V and is not compatible with 5V signals. If there are only 3.3V or few 5V signals in the system, it is recommended that you choose the cyclone series FPGA. Xilinx's products are more widely used by enterprises. Compared with Altera, Xilinx has a longer history and more customers. The reference design provided by Xilinx for chips covers a wider range of fields and more varieties than that provided by Altera. There are also more free IP cores. Xilinx's high-end FPGA has a certain advantage in the market, such as the VirtexII series, which is very successful. Actel's FPGA is mainly anti-fuse type, which is used in some specific fields; QuickLogic's CPLD is also mainly anti-fuse, generally used for product encryption, which is still difficult to ***. Its FPGA with integrated PCI hard core is a unique product, with lower cost than FPGA + PCI interface chip solution and better stability than FPGA PCI soft core solution. Lattice is also promoting low-cost FPGA products, which are introduced in more detail in the Lattice section of this forum.








2. Select FPGA model First, after selecting a certain series of FPGA, you need to select a specific model. The factors that need to be considered are as follows: A. The package mainly depends on the number of pins. If the pins are sufficient, try to choose a surface mount package, such as TQFP or QFP. The reasons why BGA is not recommended are: 1) It will increase the welding cost; 2) It increases the difficulty of wiring and may have to increase the number of PCB layers; 3) It reduces the testability and increases the test cost. Of course, if the project requires that BGA packaging must be selected, then try to choose a larger pin spacing, such as 1mm or 0.8mm. For example, for the Cyclone series of FPGAs, EP1C12 has two packages, F324 and Q240, the former is BGA and the latter is PQFP. If 150 user IOs are enough for your design, it is best to choose the latter, which can be made with a two-layer board, while the F324 package requires at least a 4-layer board. B. Resources are generally in the initial stage of design, and the scale cannot be estimated. So generally need to be selected based on experience. Generally, you should choose the largest model in the package you have determined. Generally speaking, the same package will have different capacities. For example, the PQFP240 package of the Cyclone series has two models, 1C6 and 1C12, with more than double the resources. Then you can use 1C12 for experiments in the experimental stage, and then switch to 1C6 in the future, without redesigning the PCB. Resources include logic resources (such as LE or Slice) and storage resources (such as M4K or BlockRAM). When choosing a chip, you must not only consider whether the logic resources are sufficient, but also ensure that the storage resources are sufficient. If your design uses 1000 LEs and 200Kbit of memory, if you consider the logic resources, EP1C6 is enough, with nearly 6000 LEs, but the capacity of M4K cannot meet the requirements. If you do not want to change the design, you must choose EP1C12. C. Upgradability In order to add functions or upgrade performance in the future, your FPGA must have a certain upgrade space after the design is completed. For example, if your current design uses 70% of the chip resources, then you must consider whether it can meet future needs. (The FPGA products of Xilinx and Altera are both based on SRAM. After power-on, they need an external CPU or storage to configure them before they can work. If there is interference during the configuration process, a configuration error will occur. Actel's anti-fuse FPGA, like ASIC, is solidified inside the chip and starts working when powered on, so it has stronger anti-interference performance. However, it can only be burned once, and the development cost is relatively high and the cycle is longer. It must be fully simulated, otherwise a chip will be wasted for a little difference. Altera's chips can be used for prototype verification and prototypes. After testing, if the requirements cannot be met, Actel's chips can be replaced to ensure that there are no problems with the logic part. Altera's chips currently also use some measures, such as error reconfiguration, etc., and an external CPU can also be used to configure the FPGA. After power-on, a simple test of the FPGA is performed. If there is a problem, it can be reconfigured. If the logic scale is not large, the MAXII series of CPLDs can be used. Due to the use of Flash structure, external configuration is not required, and the reliability is much higher.)

2. Selection of the main peripheral chips of FPGA Based on past experience, Red Logic recommends some chips for your reference. For chips of other applications, you can consult our website. 1. If the current of the power chip is small, you can choose the AS1117 series, surface mount package; if the current is large, you can choose the AS28xx series, surface mount package; 2. Try to choose a series with large upgrade space and pin compatibility for storage chips; SDRAM generally chooses SAMSUNG's K4S series, or Hyundai's HY57V series; ASRAM generally chooses ISSI's 61LV series; NOR FLASH generally chooses AMD's 29LV series or SST chips; NAND FLASH generally chooses SAMSUNG's K9S series;