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[avr-gcc-list] Align Data and RAM Gaps

From: Thomas D. Dean
Subject: [avr-gcc-list] Align Data and RAM Gaps
Date: Fri, 08 Aug 2014 12:43:25 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0

I have a combined C and AS application. I have to use AS because of the time restraints.

I have a 256 byte buffer that is accessed with two pointers, head and tail.

In the AS code, I want to only save the low order byte of the pointer. This is do-able, if the buffer is aligned at 0x0100.

In the C file,
char buf[256] __attribute__ ((aligned (256)));
In the AS file,
.global buf

Looking at the map file, I see

  0x0000000000800100                tx_buf_head_ptr
  0x0000000000800200                buf
  0x0000000000800300                rx_buf_tail_ptr
  0x0000000000800302                tx_buf_tail_ptr

There is a gap of 254 bytes.

How do I avoid this gap?  What determines the linker allocation order?

Tom Dean

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