[mpc5777c] Can I initialize less than 64 bits in Ram memory ?

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[mpc5777c] Can I initialize less than 64 bits in Ram memory ?

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jaejynshin
Contributor III

Hello Expert 

As I write at the below page, I found how to initialize 64 bits of Ram memory.

https://community.nxp.com/message/986762?commentID=986762#comment-986762 

But my customer wants to initialize only 1 byte of Ram memory.

As far as I know, it is impossible because the e_stmw is the only one instruction I can use to initialize the Ram.

Is there a way to initialize only 1 byte of Ram memory ?

Thank you

Jaejyn

3 Replies

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davidtosenovjan
NXP TechSupport
NXP TechSupport

No, it must be 64-bit write to completely define ECC code for data unit. Otherwise you will have ECC error on that place.

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jaejynshin
Contributor III

Thank you for your quick answer.

I want to know the reason what it must be 64 bit.

It is due to the because manual in MPC5777CRM_rev6 ? 

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Thank you

Jaejyn

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davidtosenovjan
NXP TechSupport
NXP TechSupport

I think you have answered yourself. "Less than 64-bit write" consists of read-modify-write sequence. If you have uninitialized 64-bit data word, write to any smaller portion of this word performs read-modify-write, and the read will cause ECC error exception (IVOR1 - machine check).

Initialization must be done by 64-writes, there is no other option. ECC error free data then can be accesses by less than 64-bit accesses, of course.