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Observer ebti07
Observer
312 Views
Registered: ‎10-15-2018

MMCME2_adv Register access

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Hey,

I am trying to dynamic reconfigure MMCME2_adv registers for frequency output. I have reffered xapp888 " MMCM and PLL Dynamic Reconfiguration" xilinx app note for register addresses and corresponding bitmap. Register values are straight forward but i have some confusion for reserved bits.

Like in ClkReg1 Bitmap for CLKOUT[6:0] and CLKFBOUT register (table 1), bit[12] is reserved and its description says "Retain the previous value stored here". But another register, ClkReg2 Bitmap for CLKOUT[0] (table 2) bit[15] is also reserved and its description just says "Reserved".

Do i have to read ClkReg1 and write reserved bit[12] again into that register and ClkReg2[15] is dont care, so i can write anything on that?

whats the difference between two types of reserve.

Thanks.

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Xilinx Employee
Xilinx Employee
301 Views
Registered: ‎08-10-2008

回复: MMCME2_adv Register access

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Hi ebti07,

The reserved bits are confidential information. The bit[15] of ClkReg2, may be don't care at all, or may be a critial bit that the doc forgot to emphasize on.

After all, for a more safe, general DRP process, we will always recommend you first read out the whole register value, only flip the bit(s) that needed, keep all the others same as previous, and then write this value back into the reg address. This guarantee a graceful transition of the primitives.

 

Thanks,

Ivy

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1 Reply
Xilinx Employee
Xilinx Employee
302 Views
Registered: ‎08-10-2008

回复: MMCME2_adv Register access

Jump to solution

Hi ebti07,

The reserved bits are confidential information. The bit[15] of ClkReg2, may be don't care at all, or may be a critial bit that the doc forgot to emphasize on.

After all, for a more safe, general DRP process, we will always recommend you first read out the whole register value, only flip the bit(s) that needed, keep all the others same as previous, and then write this value back into the reg address. This guarantee a graceful transition of the primitives.

 

Thanks,

Ivy

------------------------------------------------------------------------------------------------------------
Don't forget to reply, kudo, and accept as solution.
---------------------------------------------------------------------------------------------------------

View solution in original post