Lessons learned from TQ2440 LCD test failure

Test environment: TQ2440 development board (matched with TQ4.3-inch screen)

Test bibliography: "Practical Bare Metal Development of ARM Processors - Mechanisms rather than Strategies" (hereinafter referred to as "Practical Bare Metal Development")

In Chapter 13 of "Bare Metal Development Practice", the LCD controller principle and experiment are explained with a TQ3.5-inch screen. I also noticed this at the beginning, so for some main configuration parameters (listed in the parameter table of the data manual data) are configured with reference to the data manual of the TQ4.3-inch screen. And neglected to pay attention to the timing diagram in the data sheet (because at a glance, the diagram in the reference book seems to be the same as the diagram in the data manual, so I didn’t pay much attention to it and just configured it according to the timing diagram in the textbook), The root cause of my initial test failure was precisely a parameter configuration on the timing diagram.

The wrong parameter is the configuration of INVVCLK in LCDCON5:

This bit sets whether to read pixel data on the rising edge of VCLK or on its falling edge. The following is a partial screenshot of the timing diagram given in the 4.3-inch screen data manual:

It is easy to see that for the 4.3-inch screen, the pixel data is read on the falling edge of VCLK. On the contrary, the 3.5-inch screen obtains pixel data on the rising edge of VCLK.

The test failed due to a momentary negligence, and I was confused about where the problem was. I checked the parameters over and over again, but still couldn't find the problem. The more I couldn't find the problem, the more confused I became, because I always believed that I configured everything according to the data manual. The parameters are obviously correct. It seems that we have such a thinking habit that the details we ignore the first time will still habitually not pay attention to it during subsequent inspections.

The lesson learned from this failed experiment is: you must pay attention to details from the beginning, be careful, and never be careless. Nothing can be taken for granted! ! !