memory.x

@@ -3,12 +3,13 @@ MEMORY
   FLASH (rx)      : ORIGIN = 0x8000000, LENGTH = 1024K
   /* reserved for config data */
   CONFIG (rx)     : ORIGIN = 0x8100000, LENGTH = 16K
-  RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 111K
+  RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 112K - 4
   /* reserved for DFU trigger message */
-  DFU_MSG (wrx)   : ORIGIN = 0x2001BC00, LENGTH = 1K
+  DFU_MSG (wrx)   : ORIGIN = 0x2001BFFC, LENGTH = 4
   RAM2 (xrw)      : ORIGIN = 0x2001C000, LENGTH = 16K
   RAM3 (xrw)      : ORIGIN = 0x20020000, LENGTH = 64K
   CCMRAM (rw)     : ORIGIN = 0x10000000, LENGTH = 64K
 }
 
 _stack_start = ORIGIN(CCMRAM) + LENGTH(CCMRAM);
+_dfu_msg = ORIGIN(DFU_MSG);

src/dfu.rs

@@ -1,28 +1,25 @@
 use cortex_m_rt::{pre_init};
 
-/// RAM location used to store DFU trigger message
-const DFU_MSG_ADDR: usize = 0x2001BC00;
+const DFU_TRIG_MSG: u32 = 0xDECAFBAD;
 
-/// DFU trigger message
-const DFU_TRIG_MSG: usize = 0xDECAFBAD;
-
-/// Set DFU trigger
-pub unsafe fn trig_dfu() {
-    let dfu_msg_addr = DFU_MSG_ADDR as *mut usize;
-    *dfu_msg_addr = DFU_TRIG_MSG;
+pub unsafe fn set_dfu_trigger() {
+    extern "C" {
+        static mut _dfu_msg: u32;
+    }
+    _dfu_msg = DFU_TRIG_MSG;
 }
 
-/// Called by reset handler in lib.rs immediately after reset, checks if booting into dfu is needed
+/// Called by reset handler in lib.rs immediately after reset.
+/// This function should not be called outside of reset handler as 
+/// bootloader expects MCU to be in reset state when called.
 #[pre_init]
 unsafe fn __pre_init() {
+    extern "C" {
+        static mut _dfu_msg: u32;
+    }
 
-    let dfu_msg_addr = DFU_MSG_ADDR as *mut usize;
-    
-    // Check DFU trigger message
-    if *dfu_msg_addr == DFU_TRIG_MSG{
-
-        // Reset message
-        *dfu_msg_addr = 0x00000000;
+    if _dfu_msg == DFU_TRIG_MSG {
+        _dfu_msg = 0x00000000;
 
         // Enable system config controller clock
         const RCC_APB2ENR: *mut u32 = 0xE000_ED88 as *mut u32;
@@ -42,13 +39,13 @@ unsafe fn __pre_init() {
             *SYSCFG_MEMRMP | SYSCFG_MEMRMP_MAP_ROM,
         );
         
+        asm!(
             // Set stack pointer to bootloader location
-        asm!("LDR R0, =0x1FFF0000");
-        asm!("LDR SP,[R0, #0]");
-
+            "LDR R0, =0x1FFF0000",
+            "LDR SP,[R0, #0]",
             // Jump to bootloader
-        asm!("LDR R0,[R0, #4]");
-        asm!("BX R0");
+            "LDR R0,[R0, #4]",
+            "BX R0",
+        );
     }
-
 }

src/main.rs

@@ -429,8 +429,9 @@ fn main() -> ! {
                                         channels.power_down(i);
                                     }
                                     unsafe {
-                                        dfu::trig_dfu();
+                                        dfu::set_dfu_trigger();
                                     }
+                                    socket.close();
                                     SCB::sys_reset();
                                 }
                             }