An interview question

chenbingjy

An interview question [Copy link]

During the interview today, the interviewer asked me a question

A frame of data came in the serial port interrupt, but before it could be processed, another frame of data came.

What should I do?

I didn't know how to answer, so I just said something random.

Overwrite the previous frame, or save it to another variable, process the later one first, and then

Process the previous frame.

Could you please advise how to answer this? Thank you!

dcexpert

Different systems may have different processing methods. Some can discard old data, while others need to cache first and process the old data before processing the new data.

baopodao

It mainly depends on the importance of the data. For unimportant data, it is usually directly overwritten. For important data, the receiving buffer is enlarged and all are stored. Process them in sequence.

chenbingjy

Thank you

mingplus

1. If the serial port has a register such as FIFO, it can store several frames of data, and if it is not full, the new frame of data will not be lost.
2. If the serial port does not have FIFO, the old frame will be overwritten by the new one if it cannot be processed in time. "The serial port interrupt has data that cannot be processed in time, and a new one comes" --- It means that other interrupts are running, and their interrupt priority is not lower than the serial port interrupt, and their running time exceeds the interval between the two frames before and after the serial port; there are two situations: one is that the serial port data loss is not important, and the other is that there is a problem with the interrupt design.

wangerxian

There are many ways. To take the most extreme example, the data is very important and continuous and cannot be lost, and the hardware FIFO of the serial port is full.

Scenario 1: If the content of the previous frame is currently being processed, but the content of the next frame is more important, you can interrupt the processing of the current frame and save the scene. If the scene cannot be saved, save the original data of the previous frame and process the next frame first.

Scenario 2: If the data is continuous, the previous frame must be processed first, and the next frame will be stored in the self-defined cache.

Scenario 3: If an RTOS system is used, another task can be started to process the next frame of data, so that two frames of data can be processed simultaneously.

annysky2012

There are many methods. Take the most extreme case. The data is very important and continuous and cannot be lost. The hardware FIFO of the serial port is also full. Scenario 1: If the content of the previous frame is currently being processed, but the content of the next frame is more important, you can interrupt the processing of the current frame and save the scene. If the scene cannot be saved, save the original data of the previous frame and process the next frame first. Scenario 2: If the data is continuous, you must process the previous frame first, and the next frame will be stored in the cache you define. Scenario 3: If an RTOS system is used, you can start another task to process the data of the next frame, and the two frames of data can be processed at the same time.

Very accurate analysis

chenbingjy

They are all experts.

bigbat

There is another solution to handle extreme situations: the data is very important, the data is continuous, the buffer is full, and it cannot be processed temporarily. Usually, a frame structure can be added, and a data receiving response can be designed. At this time, a request can be issued to the sender to suspend sending. What if there is no response? The sender can be asked to send more than twice. The data from the two times is received together.

freebsder

If this situation is sporadic, then caching is likely to solve the problem.

If this situation is the norm, it means that your hardware system load has reached its limit and there is no room for improvement. You can consider using hardware that responds more quickly and runs faster.

If even if you spend more money on a hardware system that cannot meet your data pressure, you can only coordinate with the business to reduce the data pressure.

If none of the above works and the business pressure cannot be adjusted, consider adding another level of front-end data forwarding to distribute the pressure to two or more hardware systems.

chenbingjy

Thank you