How to use external clock generator (5P49V6965) as main clock source in imx8mp?

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How to use external clock generator (5P49V6965) as main clock source in imx8mp?

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Jimmychea
Contributor III

I intend to use external clock generator (5P49V6965) as main clock source for imx8m plus, what should i do ? any reference document that can refer to ?

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Sanket_Parekh
NXP TechSupport
NXP TechSupport

Hi @Jimmychea 

I hope you are doing well.
 
There are three clock sources available in i.MX8MP as shown below.
Screenshot (427).png

 
One can refer to Table 11. Oscillator/Crystal recommendations in i.MX 8M Plus Hardware Developer’s Guide. and  Table 5-1. Clock Root Table in i.MX 8M Plus Applications Processor Reference Manual To understand how clock sources are selected for various clock roots.
 
Thanks & Regards
Sanket Parekh
 
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Jimmychea
Contributor III

If using external clock generator (5P49V6965) to generate 24MHz and supply to Processor, is that feasible ?

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Sanket_Parekh
NXP TechSupport
NXP TechSupport

Hi @Jimmychea 

It is recommended to only use a crystal oscillator that has ESR less than 60 Ω and is rated for a drive level of at least 100 µW as described in Table 11. Oscillator/Crystal recommendations in i.MX 8M Plus Hardware Developer’s Guide.
 
Thanks & Regards
Sanket Parekh

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Jimmychea
Contributor III

From the i.MX 8M Plus Application Processor Reference Manual

5.3.2 Functional Description
The 24MHz oscillator will be used as the primary clock source for the PLLs to generate
the clock for CPU, BUS, and high-speed interfaces. For all PLLs, the 24MHz clock from
the oscillator can be used as the PLL reference clock directly.
The OSC IP used by the 24MHz XTAL module has three modes, Internal clock
generation mode, External clock receive mode and Retention mode.
During internal clock generation mode, a suitable quartz crystal is connected between
PADI and PADO to generate the clock signal at the CK pin.
During external clock generation mode, the cell acts like a buffer, reflecting the PADI
signal at CK.
The RTO (retention enable) signal retains the previous state of all the core input control
signals. Logic at the RTO signal enables the retention operation.
Each XTAL module supports the following modes through register configuration:

• Normal oscillator mode - In normal mode, the XTAL IP generates stable square
wave based on the crystal oscillator input.
• Bypass mode - In bypass mode, an external clock can be input through the XTAL
pad.

 

Does it means can use external clock generator ?

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Sanket_Parekh
NXP TechSupport
NXP TechSupport

Hi @Jimmychea ,

One can use an external clock generator for a 24 MHz reference clock.
Please refer to the points mentioned in  3.1.6 External clock sources in i.MX 8M Plus Applications Processor Datasheet.
 
Thanks & Regards,
Sanket Parekh
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khang_letruong
Senior Contributor III

HI @Jimmychea ,

I am not sure if it is a good idea to use it as main clock source for the CPU. One idea could be using external MCU to pre-configure its registers via I2C interface to output necessary clocks for iMX8MP processor.

Regards,
Khang

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Jimmychea
Contributor III

how about if use it as main clock source for imx8mp processor ?

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