[ion] N0200: improve code spliting between internal/external flash

Part I: move peripherals initiation to be executed from the external
flash to avoid many dependencies to limit the number of functions that
are forced in internal flash.

ion/src/device/n0200/drivers/board.cpp

@@ -1,6 +1,7 @@
 #include <drivers/board.h>
 #include <drivers/cache.h>
 #include <drivers/config/clocks.h>
+#include <drivers/external_flash.h>
 #include <regs/regs.h>
 #include <ion.h>
 
@@ -85,7 +86,7 @@ void initMPU() {
   Cache::isb();
 }
 
-void init(bool initBacklight) {
+void init() {
   initFPU();
   initMPU();
   initClocks();
@@ -106,7 +107,7 @@ void init(bool initBacklight) {
     GPIO(g).PUPDR()->set(0x00000000); // All to "None"
   }
 
-  initPeripherals(initBacklight);
+  ExternalFlash::init();
   // Initiate L1 cache after initiating the external flash
   Cache::enable();
 }

ion/src/device/n0200/flash.ld

@@ -48,12 +48,12 @@ SECTIONS {
 
   /* Internal flash memory */
 
-  /* We link 'non_inlined_ion_main' in a separate section from text.internal.
+  /* We link 'jump_to_external_flash' in a separate section from text.internal.
    * Indeed, it is the only internal flash symbol that refers the external
    * flash. This way we can assert that there are no cross references from the
    * internal flash to the external flash. */
   .text.internal_to_external : {
-    *(.text._ZL20non_inlined_ion_mainv)
+    *(.text._ZL22jump_to_external_flashv)
   } >INTERNAL_FLASH
 
   /* Use boot routine and required dependencies */
@@ -61,38 +61,44 @@ SECTIONS {
    * done with -fdata-sections -ffunction-sections */
   .text.internal : {
     . = ALIGN(4);
-    *(.text.__assert)
-    *(.text.start)
     *(.text.abort)
     *(.text.isr_systick)
+    *(.text.__assert)
     *(.text.memcpy)
+    *(.text.memset)
+    /*
     *(.text.strlen)
     *(.text.strncmp)
     *(.text.strlcpy)
     *(.text.strcmp)
-    *(.text.memset)
     *(.text.memmove)
-    *(.text._ZN3Ion*)
-    *(.text._ZNV3Ion*)
-    *(.text._ZNK3Ion*)
-    *(.text.LZ4_*)
+    */
+    /* 'start' dependecies */
+    *(.text.start)
+    *(.text._ZN3Ion6Device5Board4initEv)
+    *(.text._ZN3Ion6Device5Board7initFPUEv)
+    *(.text._ZN3Ion6Device5Board7initMPUEv)
+    *(.text._ZN3Ion6Device5Board10initClocksEv)
+    *(.text._ZNV3Ion6Device4Regs8Register*)
+    *(.text._ZN3Ion6Device4Regs8Register*)
+    *(.text._ZNK3Ion6Device4Regs9AFGPIOPin*)
+    *(.text._ZN3Ion6Device13ExternalFlash*)
+    *(.text._ZN3Ion6Device5Cache*)
+    *(.text._ZN3Ion6Timing6usleepEj)
+
+    /* 'abort' dependcies */
+    *(.text._ZN3Ion6Device5Reset4coreEv)
+
+    /**(.text._ZN3Ion5Power7suspendEb)*/
+
+    /* Optimization */
     */libgcc.a:(.text)
   } >INTERNAL_FLASH
 
 
   .rodata.internal : {
     . = ALIGN(4);
-    *(.rodata.dfu_bootloader)
-    *(.rodata)
-    *(.rodata.str1.1)
-    *(.rodata._ZN3Ion*)
-    *(.rodata._ZZN3Ion*)
-    *(.rodata._ZNK3Ion*)
-    *(.rodata._ZTVN3Ion6*)
-    *(.rodata._ZN3KDColor*)
-    *(.rodata._ZL11KDColor*)
-    *(.rodata._ZL12KDColor*)
-    *(.rodata._ZL13KDColor*)
+    *(.rodata._ZN3Ion6Device13ExternalFlash*)
   } >INTERNAL_FLASH
 
   /* External flash memory */
@@ -103,6 +109,7 @@ SECTIONS {
   } >EXTERNAL_FLASH
 
   .rodata.external : {
+    *(.rodata)
     *(.rodata.*)
   } >EXTERNAL_FLASH
 

ion/src/device/shared/boot/rt0.cpp

@@ -27,7 +27,23 @@ void abort() {
 #endif
 }
 
-/* This additional function call 'non_inlined_ion_main' serves two purposes:
+/* In order to ensure that this method is execute from the external flash, we
+ * forbid inlining it.*/
+
+static void __attribute__((noinline)) external_flash_start() {
+  /* Init the peripherals. If there is the on boarding app, do not initialize the
+   * backlight so that the user does not see the LCD tests. The backlight will
+   * be initialized after the Power-On Self-Test.*/
+#if EPSILON_ONBOARDING_APP == 0
+  Ion::Device::Board::initPeripherals(true);
+#else
+  Ion::Device::Board::initPeripherals(false);
+#endif
+
+  return ion_main(0, nullptr);
+}
+
+/* This additional function call 'jump_to_external_flash' serves two purposes:
  * - By default, the compiler is free to inline any function call he wants. If
  *   the compiler decides to inline some functions that make use of VFP
  *   registers, it will need to push VFP them onto the stack in calling
@@ -40,16 +56,20 @@ void abort() {
  *   start(), we isolate it in its very own non-inlined function call.
  * - To avoid jumping on the external flash when it is shut down, we ensure
  *   there is no symbol references from the internal flash to the external
- *   flash except the jump to ion_main. In order to do that, we isolate this
+ *   flash except this jump. In order to do that, we isolate this
  *   jump in a symbol that we link in a special section separated from the
  *   internal flash section. We can than forbid cross references from the
  *   internal flash to the external flash. */
 
-static void __attribute__((noinline)) non_inlined_ion_main() {
-  return ion_main(0, nullptr);
+static void __attribute__((noinline)) jump_to_external_flash() {
+  external_flash_start();
 }
 
-void start() {
+/* When 'start' is executed, the external flash is supposed to be shutdown. We
+ * thus forbid inlining to prevent executing this code from external flash
+ * (just in case 'start' was to be called from the external flash). */
+
+void __attribute__((noinline)) start() {
   /* This is where execution starts after reset.
    * Many things are not initialized yet so the code here has to pay attention. */
 
@@ -90,16 +110,12 @@ void start() {
   }
 #endif
 
-  /* Init the board. If there is the on boarding app, do not initialize the
-   * backlight so that the user does not see the LCD tests. The backlight will
-   * be initialized after the Power-On Self-Test.*/
-#if EPSILON_ONBOARDING_APP == 0
-  Ion::Device::Board::init(true);
-#else
-  Ion::Device::Board::init(false);
-#endif
+  Ion::Device::Board::init();
 
-  non_inlined_ion_main();
+  /* At this point, we initialized clocks and the external flash but no other
+   * peripherals. */
+
+  jump_to_external_flash();
 
   abort();
 }

ion/src/device/shared/drivers/board.cpp

@@ -42,11 +42,9 @@ void initPeripherals(bool initBacklight) {
   Console::init();
   SWD::init();
   Timing::init();
-  ExternalFlash::init();
 }
 
 void shutdownPeripherals(bool keepLEDAwake) {
-  ExternalFlash::shutdown();
   Timing::shutdown();
   SWD::shutdown();
   Console::shutdown();

ion/src/device/shared/drivers/board.h

@@ -5,7 +5,7 @@ namespace Ion {
 namespace Device {
 namespace Board {
 
-void init(bool initBacklight = true);
+void init();
 void shutdown();
 
 void initFPU();