Fix RAM address and add ITCM and DTCM sections

Previously DTCM region was simply added to RAM region, this can cause problems with DMA as DMA does not have access to DTCM region.
See page 71 and 76 in data sheet RM0410 Rev 4.

#123

Signed-off-by: Moritz Scheuren <[email protected]>

memory_2048_368.x

@@ -3,9 +3,32 @@ MEMORY
 {
   /* NOTE K = KiBi = 1024 bytes */
   FLASH : ORIGIN = 0x08000000, LENGTH = 2M
-  RAM : ORIGIN = 0x20000000, LENGTH = 368K + 16K
+  RAM : ORIGIN = 0x20020000, LENGTH = 368K + 16K
+  ITCM : ORIGIN = 0x00000000, LENGTH = 16K /* Instruction Tighly Coupled Memory */
+  DTCM : ORIGIN = 0x20000000, LENGTH = 128K /* Data Tighly Coupled Memory */
 }
 
+SECTIONS
+{
+    .itcm : ALIGN(4)
+    {
+        *(.itcm .itcm.*);
+        . = ALIGN(4);
+    } > ITCM
+
+    .dtcm : ALIGN(4)
+    {
+        *(.dtcm .dtcm.*);
+        . = ALIGN(4);
+    } > DTCM
+}
+
+/* You can then use something like this to place a variable into a specific section of memory:
+ *  #[link_section = ".dtcm.BUFFER"]
+ *  static mut BUF: [u8; 1024] = [3u8; 1024];
+ *  Verifiable with: cargo size --release --example hello_world -- -A
+ */
+
 /* This is where the call stack will be allocated. */
 /* The stack is of the full descending type. */
 /* NOTE Do NOT modify `_stack_start` unless you know what you are doing */