How to configure RTT with a fixed address in IAR

Question

Hello.
I am using RTT successfully with nrf52 and IAR. But the start address for the RTT control block is a moving target: it changes whenever my code changes. I want to assign this block a specific memory section starting at 0x20000000 in ram and placing stack and heap thereafter.
Therefore, I changed the SEGGER Real-time-Terminal control block (CB) initialization in SEGGER_RTT.c like this: Instead of the definition 
 SEGGER_RTT_CB _SEGGER_RTT;
 
 that placed SEGGER_RTT on the stack, I define: 
 #pragma section = "RTT"
#define RTT_CONTROL_BLOCK_ADDRESS ((unsigned)__section_begin("RTT"))
#define _SEGGER_RTT (*((SEGGER_RTT_CB *) RTT_CONTROL_BLOCK_ADDRESS))
 
 In the nrf52xxx_xxaa.icf configuration file, I added the following lines: 
 define symbol Size_RTT = 0x1000;
define block RTT with alignment = 8, size = Size_RTT { };

define block FIXED_ORDER_RAM with fixed order { block RTT, block CSTACK, block HEAP };
 
 and changed the place in directive 
 place in RAM_region { readwrite, block CSTACK, block HEAP };
 
 like so: 
 place in RAM_region { readwrite,
 first block FIXED_ORDER_RAM };
 
 In the debugger, RTT_CONTROL_BLOCK_ADDRESS evaluates correctly to 0x20000000, but the J-Link Viewer does not find it. What am I doing wrong? 
 Thx in advance! 
 PS: The complete icf-file including my changes: 
 /*###ICF### Section handled by ICF editor, don't touch! ****/
/*-Editor annotation file-*/
/* IcfEditorFile="$TOOLKIT_DIR$\config\ide\IcfEditor\cortex_v1_0.xml" */
/*-Specials-*/
define symbol __ICFEDIT_intvec_start__ = 0x00000000;
/*-Memory Regions-*/
define symbol __ICFEDIT_region_ROM_start__ = 0x00000000;
define symbol __ICFEDIT_region_ROM_end__ = 0x0007FFFF;
define symbol __ICFEDIT_region_RAM_start__ = 0x20000000;
define symbol __ICFEDIT_region_RAM_end__ = 0x2000FFFF;
/*-Sizes-*/
define symbol __ICFEDIT_size_cstack__ = 0x2000;
define symbol __ICFEDIT_size_heap__ = 0x2000;
/**** End of ICF editor section. ###ICF###*/

define memory mem with size = 4G;
define region ROM_region = mem:[from __ICFEDIT_region_ROM_start__ to __ICFEDIT_region_ROM_end__];
define region RAM_region = mem:[from __ICFEDIT_region_RAM_start__ to __ICFEDIT_region_RAM_end__];

define block CSTACK with alignment = 8, size = __ICFEDIT_size_cstack__ { };
define block HEAP with alignment = 8, size = __ICFEDIT_size_heap__ { };

define symbol Size_RTT = 0x1000;
define block RTT with alignment = 8, size = Size_RTT { };

define block FIXED_ORDER_RAM with fixed order { block RTT, block CSTACK, block HEAP };

initialize by copy { readwrite };
do not initialize { section .noinit };

place at address mem:__ICFEDIT_intvec_start__ { readonly section .intvec };
place in ROM_region { readonly };
place in RAM_region { readwrite,
 first block FIXED_ORDER_RAM };

stephan · Accepted Answer

Looks like I found a solution myself: 
In ICF one must define the section RTT_section: 
 define block RTT with alignment = 8, size = Size_RTT { section RTT_section };
 
 and the block can just be put first into RAM: 
 place in RAM_region { first block RTT, readwrite, block CSTACK, block HEAP };
 
 In SEGGER_RTT.c, the definition of _SEGGER_RTT can be rewritten with "@" directive in order to place it in the previously introduced section: 
 SEGGER_RTT_CB _SEGGER_RTT @ "RTT_section";
 
 Start of RTT block is at 0x20000000 as expected and other stuff will be placed thereafter. 
 Comple ICF: 
 /*###ICF### Section handled by ICF editor, don't touch! ****/
/*-Editor annotation file-*/
/* IcfEditorFile="$TOOLKIT_DIR$\config\ide\IcfEditor\cortex_v1_0.xml" */
/*-Specials-*/
define symbol __ICFEDIT_intvec_start__ = 0x00000000;
/*-Memory Regions-*/
define symbol __ICFEDIT_region_ROM_start__ = 0x00000000;
define symbol __ICFEDIT_region_ROM_end__ = 0x0007FFFF;
define symbol __ICFEDIT_region_RAM_start__ = 0x20000000;
define symbol __ICFEDIT_region_RAM_end__ = 0x2000FFFF;
/*-Sizes-*/
define symbol __ICFEDIT_size_cstack__ = 0x2000;
define symbol __ICFEDIT_size_heap__ = 0x2000;
/**** End of ICF editor section. ###ICF###*/

define memory mem with size = 4G;
define region ROM_region = mem:[from __ICFEDIT_region_ROM_start__ to __ICFEDIT_region_ROM_end__];
define region RAM_region = mem:[from __ICFEDIT_region_RAM_start__ to __ICFEDIT_region_RAM_end__];

define block CSTACK with alignment = 8, size = __ICFEDIT_size_cstack__ { };
define block HEAP with alignment = 8, size = __ICFEDIT_size_heap__ { };

define symbol Size_RTT = 0x1000;
define block RTT with alignment = 8, size = Size_RTT { section RTT_section };

initialize by copy { readwrite };
do not initialize { section .noinit };

place at address mem:__ICFEDIT_intvec_start__ { readonly section .intvec };
place in ROM_region { readonly };
place in RAM_region { first block RTT,
 readwrite,
 block CSTACK, block HEAP };

How to configure RTT with a fixed address in IAR

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