2009-04-28 09:31:01 Regarding DMA section in kernel

Hari Prasad (INDIA)

Message: 73369

Hi,

Following is the memory map of 2008R1.5 kernel:

Memory map:

text = 0x00180000-0x00268140

rodata = 0x00269000-0x002c3658

data = 0x002c4000-0x002d4000

stack = 0x002c4000-0x002c6000

init = 0x002d4000-0x0079d000

bss = 0x0079d000-0x00849fb8

available = 0x00849fb8-0x03eff000

DMA Zone = 0x03f00000-0x04000000

In our application, we dont need any DMA zone. If so, can we use the memory slot set apart for DMA zone in our application and if possible, how it can be done?

Pls clarify

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2009-04-28 11:07:36 Re: Regarding DMA section in kernel

Robin Getz (UNITED STATES)

Message: 73377

Hari:

You control the size of uncached memory (the DMA Zone) in the Kernel's config -> Blackfin Processor Options -> Uncached DMA region -> Disable DMA region.

Then it will be released to the normal memory pool. - and any calls allocate coherant memory will fail.

-Robin

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2009-05-05 00:21:06 Re: Regarding DMA section in kernel

Hari Prasad (INDIA)

Message: 73604

Hi Robin,

I made the necessary changes in make menuconfig to disable memory allocation of 1024K for DMA. After compiling the kernel and booting the uImage, when I give the 'free' command, I see an increase in the 'used' memory section while I expected the memory that was released from being blocked for DMA to be present in the 'free' memory section. Could you please let me know how I can retrieve this memory from 'used' section so that I can use it in my application.

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2009-05-05 00:26:41 Re: Regarding DMA section in kernel

Mike Frysinger (UNITED STATES)

Message: 73605

if you're using the UART, then it's going to go from DMA to PIO which means it needs to allocate memory from the heap rather than from the dedicated DMA section

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2009-05-05 01:48:05 Re: Regarding DMA section in kernel

Hari Prasad (INDIA)

Message: 73608

Thanks Mike