Tuesday, January 11, 2011

Weak current College】 【hardware project development experience】.

1 a full understanding of the design requirements, determine the right solution

Start a hardware development project, the original impetus will come from many areas, such as the needs of the market, based on the needs of the entire system architecture, and application software sector capabilities required, improve system capacity needs certain aspects and so on, so as a hardware system designer, you want to take the initiative to understand the different needs, and taken together, offer the most suitable hardware solutions. For example, A project of the original impetus came from a senior level within the company, their software teams in practice found the original processor board IP forwarding capacity cannot meet the requirements for system configuration and usage will cause great inconvenience, they presented the new hardware requirements. Under this objective, the programme is targeted in the hardware of the choice of two high-performance network processors, then you also need in-depth and software designers to determine the memory size, internal structure, the external interface and the amount of debugging interfaces and types, and so on details, such as software professionals like will control signaling pathways and data paths completely separate, so that in the determination of the internal data to the time to carefully consider. The beginning of the project is the need to hold a lot of discussion meetings, should be invited to participate in all relevant sectors, the benefits are three, first you can fully understand your needs in order to avoid missing important system design features, the second is to allow departments to understand the project ahead of time and personnel to do collaborative preparations, the third is from emotional stresses, in the design of the various departments involved in the project becomes all of a painstaking, will get you all care and good cooperation, on completion of the work is very helpful.

2 Schematic diagram design should pay attention to the issue of

Schematic design should have "borrowed", now the chip manufacturers can generally provide reference design schematics, so try to use these resources to fully understand the reference design, do some of your own play. When the main chip selected, one of the most critical design includes power around the clock and the interconnection between the chip.

Power supply is to ensure that hardware basis for the system to work properly, design to detailed analysis: system capable of providing power input; veneer produced power output needed; all the power you need to provide the current size; power circuit efficiency; the power to allow the fluctuation range; the entire power system needs of power-up sequence, and so on. For example, A project network processor core voltage 1.25V as needed, requiring accuracy is + 5%-3%, the current need of about 12A from these requirements, design a 5V power supply input, use Linear switching power supply controller and IR of MOSFET structures suitable power supply circuits, precision determines the output capacitor ESR of choice, and to prevent excessive current cause of dropout, joined the distal feedback function.

Clock circuit for the target circuit of jitter, A project to GE's PHY devices, beginning with an internal band PLL zero delay clock distribution chips provide 100MHz clock, GE link on packet loss, later replaced by simple clock Buffer device solves the problem of packet loss, it is the internal PLL introduces jitter.

Chip interconnection between the data that you want to ensure the accuracy of transmission, in this connection, high-speed differential signal lines with high speed, good wiring, signal integrity and other characteristics, A project of the interconnection between multiple chips are made of a high-speed differential signal line in the debug and test the problem does not occur.

3PCB design should pay attention to the issue of

PCB design to achieve the purpose of clarity, for important signal line to very strict requirements on the length of the wiring and processing to loop, and for low-speed and not important signal lines can be placed in a slightly lower on the priority of the wiring. Important part including: power of segmentation; memory clock line, control line and cable length requirements; high-speed differential line wiring, etc.

A project in memory chip enables 1G size DDRmemory, for this part of the wiring is very critical, taking into account the control line and the address line topology distribution, the data and clock line length differential control in the realization of the process, according to the chip data manual and the actual frequency can conclude specific routing rules require, for example, the same group of cable length difference must not exceed the number of mil, each path length difference between cannot exceed number of mil and so on.

When these requirements determine after which you can explicitly request the PCB designers to achieve, if the design of all important routing requirements are clear, you can convert the whole cabling constraints, use CAD automatic routing tool software for PCB design, which is in the high-speed PCB design of a trend.

4 checking and debugging

When preparing to debug a Board, it must be serious about doing a Visual inspection, inspection of the welding process is visible short circuit and PIN on Tin fault, check to see if any component model, placing the error first foot placement errors, missing Assembly, and then use the power supply to the multimeter measurement of resistance, to check whether there is a short circuit, the good habits to avoiding the risk of damage to the Board after power on. Debugging process to have peace of mind, I found the problem is very good, need to do is to do more analysis and comparison, the gradual elimination of possible reasons to believe that "everything is a solution to the problem of" and "there must be a reason for it, so that the final" must be able to debug successfully.

5 some summation

Now from a technical point of view, each design ultimately can make out, but the success of a project, just depends on the technical implementation, and finish time, the quality of the products, the team with the closely related, so good teamwork, transparent open itemsHead of communication, research and development of precise and meticulous arrangement, ample supplies and personnel arrangements, so as to guarantee the success of a project.

A good hardware engineer actually is a project manager, he/she needs from outside Exchange gets on your design needs, and then summarize, analyze the hardware implementation of a specific. But also with many chip and package vendor, select the appropriate options when the diagram is complete, he or she should be organized to meet the accreditation of colleagues and check, and CAD engineers working together to complete PCB design. At the same time, be prepared to BOM list, started purchasing and preparing materials, contact processing factory completed plate mounting. In the debugging process he/she must organize good software engineers to work together with the test key debugging engineer to solve issues found during the test, wait until the product introduction to the site, if you have problems, you also need to ensure timely support. So do a hardware designers to exercise out of good communication skills, ability to face the pressures of the regulation, the same time processing multiple transaction coordination and decision making abilities and good peace of mind, and so on.

There are carefully and conscientiously, because hardware design on a small oversights often resulting in very large economic losses, such as previously come across a piece of plate PCB design complete out manufacturing file mishandling causing power and stratigraphic even together, PCB manufacturing is finished and no check directly on line mount, to the test of time only to find the shortest path problem, but components are soldered to the Board, resulting in the loss of hundreds of thousands. So careful and serious examination responsible test, and accumulation of learning, in order to make a hardware designers continued progress, then some small industry.

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