RTOS/AM3359: Memory alignment

Andrew Hatko

Prodigy 100 points

Part Number: AM3359

Tool/software: TI-RTOS

I have question about memory alignment when writing/reading to the eMMCSD memory.

The example program uses the following code:

#define DATA_BUF_ALIGN (256)

uint8_t tx[SECTORSIZE*TESTSECTORS];
#ifdef __ARM_ARCH_7A__
__attribute__((aligned(256))) // GCC way of aligning
#endif

uint8_t rx[SECTORSIZE*TESTSECTORS];
#ifdef __ARM_ARCH_7A__
__attribute__((aligned(256))) // GCC way of aligning
#endif

The first question is why data should be aligned at 256 bytes?

How and were DATA_BUF_ALIGN is used?

What is scope of this definition?

How to correctly align data if I am using alloc function for large block of the DDR?

Thank you.

over 7 years ago

0 Biser Gatchev-XID over 7 years ago

TI__Guru**** 393215 points

The RTOS team have been notified. They will respond here.

0 Lalindra Jayatilleke over 7 years ago

TI__Mastermind 30365 points

Andrew,

Sorry for the delayed response. I was trying to track down a response for you.
The 256 bytes is to do with the DDR buffer cache alignment for DMA mode.

Lali

0 Andrew Hatko over 7 years ago in reply to Lalindra Jayatilleke

Prodigy 100 points

Thank you. Size of the used buffer can determine how memory should be aligned.

Still having number of bytes we want memory to be aligned, I am not sure what is proper way of programming this.

Particularly what causes that memory in TI example is correctly aligned?

Thanks,

Andrew

0 Karl Wechsler over 7 years ago in reply to Andrew Hatko

TI__Mastermind 20805 points

I don't know why this buffer needs to be aligned. I'm guessing that the MMC peripheral or DMA might have that requirement.

You can use Memory_alloc() to allocate an aligned memory block rom the heap at runtime. This API has an alignment parameter.

This link might help:

e2e.ti.com/.../204052

0 Andrew Hatko over 7 years ago in reply to Karl Wechsler

Prodigy 100 points

Thank you. I did not know about Memory_alloc().

Andrew

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RTOS/AM3359: Memory alignment