Recently with SSD2828 drive Xiaomi screen, no code, no technical support, their own code to write repeatedly debugging, the whole dead I, now can display the picture, do a bus to share with you, said the wrong place welcome everyone to criticize correct.
Points:
1. Xiaomi 3 screen resolution is 1920*1080, 24bit, row and column Pixel point is 1080*1920, the default display way is from left-to-right, up-down, this can be modified by DCS instructions.
2. The SSD2828 manual says the SSD2828 line can display a maximum of 1920 pixels (60HZ), while the official network says SSD2828 's maximum resolution is 1920x1200, so I always thought SSD2828
Row pixels can be set to a maximum of 1920, column maximum pixels can be set to 1200, in fact, when driving Xiaomi 3 screen, the rows and columns were set to 1080*1920.
3. To use SSD2828 's latest manual, the current can be found is V1.3, the old version of some places is wrong, misleading people.
4. The SSD2828 RGB interface and the number of bits of the MIPI interface are set together (via B6 register settings), that is, there is no RGB for the 24bit,mipi of this case. 16bit.
5. SSD2828 can support the 16,18,24bit screen, and some screen does not support 16bit, such as Xiaomi 3 screen is not supported, this should be seen clearly.
6. The data Lane and SSD2828 of the screen are set to the same
7. SSD2828 vbp, VFP, HBP, HFP, and CPU this terminal settings can not be consistent, the display is not normal, I do not know why.
Driver initialization includes initialization of the SSD2828,LCD screen
1. SSD2828 initialization mainly has the setting of the PLL, setting LCD parameters (resolution, VBP, VFP, HBP, HFP).
CPU this end of the PCLK set to 90~120mhz, SSD2828 PLL output of about 800MHz, more than 900 some dangerous, interference large (with the PCB is related to)
2. SSD2828 provides to the CPU interface, through the DCs to set some LCD parameters, this depends on the LCD manual which parameters to set, the most important is the 0X29,0X11 Directive,
Let the LCD exit sleep mode and display on.
Screen does not display there may be several situations
1.0x29,0x11 command sent wrong, LCD confiscated, has been in sleep state.
2. Screen to show that there must be a wave on the data lane, if the data Lane wave type is not, that is, ssd2828 is not configured, and the CPU is not related to this side.
3. Data Lane has a wave type, may be related to C9, CA, CB, these registers, arbitrarily set a few values to try (max, Min, median), I debug a week, that is, C9 not set to, so has not been shown
Screen jitter may be related to VbP, VFP, HBP, HFP, these parameters, modify the SSD2828 and CPU LCD controler These parameters try
Color over-distortion, right can be associated with the pclk_p in the B6 register and the Clk_delay_sel in 0xDB, I set the pclk_p to 1, Clk_delay_sel 0, the display picture is good.
No, you can modify Clk_delay_sel try it, I can't do it again.
In addition to the parameters that must be set, the registers that affect the display are mainly:
C9, CA, CB, DB, DD, ED, these registers are mainly modified in debugging
See a lot of friends to 2828 this chip is very interested, I will open some information, the CPU is AM335X-1G CPU, no running system, using naked machine developed; speed has been open to the maximum,
To refresh the Xiaomi screen 1080P is still very slow, finally all the pictures are preloaded into RAM, the display of the time to switch layers, am335x is a double layer. If you need to use a different CPU, you can compare it with am335x.
Performance is satisfied, SD2828 this chip a bit of a problem, with CPU connected IO has leakage phenomenon, resulting in am335x start a little problem, SD2828 data, this chip is really difficult to adjust, high frequency, parameter configuration is not good cause display. To modify the parameters, refer to the several registers I provided, then I also changed blood to show.
Resource-mipi screen debug record everyone do not download, give a free connection https://pan.baidu.com/s/1jIQT7Ky
