ov5640 VCO frequency calculation

[RomanLut]

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Issue or Suggestion Description

1. ov5640 driver sets:

esp32-camera/sensors/ov5640.c

Line 442 in ddd00c5

ret = set_pll(sensor, false, sys_mul, 4, 2, false, 2, true, 4);

//Set PLL: bypass: 0, multiplier: sys_mul, sys_div: 4, pre_div: 2, root_2x: 0, pclk_root_div: 2, pclk_manual: 1, pclk_div: 4

VCO = XCLK / pre_div * multiplier = 20000000 / 2 * 180 = 1800 MHz

which is way too high the limit 500-1000Mhz of PLL1 output:

So how does it work?

2. In the code VCO is calculated differently to diagram and application note, with division by root_2x_div:

esp32-camera/sensors/ov5640.c

Line 192 in ddd00c5

unsigned int VCO = REFIN * pll_multiplier / root_2x_div;

Why?

[RomanLut]

Update: I am actually trying to understand which PCLK and FPS result from a given set of parameters by implementing a frequency calculator:
https://romanlut.github.io/hx-esp32-cam-fpv/tools/ov5640_pclk_calculator/ov5640_pclk_calculator.html

The diagram shown above appears to be incorrect. It seems to have been removed in later revisions of the datasheet. There are comments in the driver code that describe a different way to calculate the frequencies, but those calculations still do not match the actual observed results.

esp32-camera/sensors/ov5640.c

Line 200 in ddd00c5

ESP_LOGI(TAG, "Calculated XVCLK: %d Hz, REFIN: %u Hz, VCO: %u Hz, PLL_CLK: %u Hz, SYSCLK: %u Hz, PCLK: %u Hz", xclk, REFIN, VCO, PLL_CLK, SYSCLK, PCLK);

[AxelLin]

Issue or Suggestion Description

1. ov5640 driver sets:

esp32-camera/sensors/ov5640.c

Line 442 in ddd00c5

ret = set_pll(sensor, false, sys_mul, 4, 2, false, 2, true, 4);
//Set PLL: bypass: 0, multiplier: sys_mul, sys_div: 4, pre_div: 2, root_2x: 0, pclk_root_div: 2, pclk_manual: 1, pclk_div: 4

VCO = XCLK / pre_div * multiplier = 20000000 / 2 * 180 = 1800 MHz

which is way too high the limit 500-1000Mhz of PLL1 output:

Hi @me-no-dev,

Any comment for this question?
Maybe the sys_mul value is too high?
BTW, the datasheet from https://cdn.sparkfun.com/datasheets/Sensors/LightImaging/OV5640_datasheet.pdf says:
The OV5640 PLL allows for an input clock frequency ranging from 6~27 MHz and has a maximum VCO frequency of 800 MHz

[AxelLin]

Hi @me-no-dev

Could you take a look?

I think the logic to decide pre_div and sys_mul needs update
to ensure VCO meets SPEC.

BTW, the pll_pre_div2x_map seems wrong https://github.com/espressif/esp32-camera/blob/master/sensors/ov5640.c#L179
The datasheet says
0x3037 SC PLL CONTRL3
Bit[3:0]: PLL pre-divider 1,2,3,4,6,8

[me-no-dev]

Will have a look when I have some spare time. Else any answer will not be full here. All clocks and settings have been fully tested and working. I am not sure why the issue is raised? Is this just a question? Or did you experience problems?

[mabuware]

there is definitely something fishy going on with the current settings of the OV5640. I have a standalone USB board for the ov5640 that gives me with the same ov5640 module an infinitely better stream and it also doesn't heat up as much as when using it with the esp32 and this library.

I hooked up an I2C sniffer onto that board and have documented the stream here:

#172 (comment)

I haven't gotten around to pinpoint the necessary changes yet to make it work as well as this USB board does.

[github-actions]

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