[En-Nut-Discussion] branches/devnut_m3n: _vtable needs 512 Byte alignment

[Uwe Bonnes]

Hello,

_vtable in the linker script needs 512 Byte alignement

(from pm0056.pdf:)
4.4.4           Vector table offset register (SCB_VTOR)
           Bits 31:30 Reserved, must be kept cleared
           Bits 29:11 TBLOFF[29:9]: Vector table base offset field.
                       It contains bits [29:9] of the offset of the table
                base from memory address 0x00000000. When
                       setting TBLOFF, you must align the offset to the
                number of exception entries in the vector table.
                       The minimum alignment is 128 words. Table alignment
                requirements mean that bits[8:0] of the
                       table offset are always zero.


For the original linker script one doesn't notice, as _vtable is the first
item in SRAM0. However if you want to run from SRAM, like with the linker
script modified like below, _vtable may get placed inappropriate.

To not waste RAM space however, probably best is to place the _vtable
definition first. The alignement directive should be changed however.


Bye
-- 
Uwe Bonnes                bon at elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------
Index: nut/arch/cm3/ldscripts/stm32f10x_flash.ld
===================================================================
--- nut/arch/cm3/ldscripts/stm32f10x_flash.ld	(Revision 3518)
+++ nut/arch/cm3/ldscripts/stm32f10x_flash.ld	(Arbeitskopie)
@@ -4,8 +4,6 @@
  *
  ***********************************************************************************/
 
-PROVIDE (__heap_start = _sheap);
-
 _ramend = ORIGIN(SRAM0) + LENGTH(SRAM0);
 
 SECTIONS
@@ -23,11 +21,11 @@
     	*(.gcc_except_table)
 	    . = ALIGN(4);
         _etext = .;
-    } > FLASH0
+    } > SRAM0
 
     .vtable (NOLOAD):
     {
-    	. = ALIGN(4);
+    	. = ALIGN(512);
 	    _vtable = .;
 	    *(.vtable*)
     	. = ALIGN(4);
@@ -67,16 +65,9 @@
         _pspstack_start = .;
         KEEP(*(.psp_stack .psp_stack.*));
         _pspstack_end = .;
-    } > SRAM0
+        PROVIDE (__heap_start = .);
+   } > SRAM0
 
-    .heap (NOLOAD):
-    {
-        . = ALIGN(4);
-        _sheap = .;
-        . = _ramend - .;
-        _eheap = .;
-    } > SRAM0
-
 end = .;
 /*
     DISCARD :