DDR reserved bits cleared during boot

pavelstanek — Tue, 05 Apr 2016 14:04:36 GMT

Hello,

I have small question about reserved bits in DDR subsystem.

Let's use i.MX6Q sabre board (mx6qsabresd) , and nearly any Linux SDK.

Let's picup some register, for example IOMUXC_SW_PAD_CTL_PAD_DRAM_ODT0 (0x020e059c), but there are others with same problem.

In documentation there is that reset value is 0x00003030

In U-boot there are records in *.cfg files (for device configuration block - ROM init) like

DATA 4, 0x020e059c, 0x00000030

So this will set DSE value of pin, but also clears reserved bits (bits 15-12) during ddr init by rom code.

Is it correct to clear these reserved bits? Are they useful for anything?

And is it safe to clear them?

Re: DDR reserved bits cleared during boot

Yuri — Wed, 06 Apr 2016 09:07:02 GMT

Hello,

The reserved bits concern with preliminary i.MX6 specs, where PUE and PKE
bits were used (to define pull up options). Strictly speaking, initialization code should

follow recent RM recommendations.

Have a great day,
Yuri

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i.MX ProcessorsのトピックDDR reserved bits cleared during boot

DDR reserved bits cleared during boot

Re: DDR reserved bits cleared during boot