initial check in based on SVN revision 575

source/semihost_hardfault.c

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+// ****************************************************************************
+// semihost_hardfault.c
+//                - Provides hard fault handler to allow semihosting code not
+//                  to hang application when debugger not connected.
+//
+// ****************************************************************************
+// Copyright 2017-2022 NXP
+// All rights reserved.
+//
+// NXP Confidential. This software is owned or controlled by NXP and may only be
+// used strictly in accordance with the applicable license terms.
+//
+// By expressly accepting such terms or by downloading, installing, activating
+// and/or otherwise using the software, you are agreeing that you have read, and
+// that you agree to comply with and are bound by, such license terms.
+// 
+// If you do not agree to be bound by the applicable license terms, then you may not
+// retain, install, activate or otherwise use the software.
+// ****************************************************************************
+//
+//                       ===== DESCRIPTION =====
+//
+// One of the issues with applications that make use of semihosting operations
+// (such as printf calls) is that the code will not execute correctly when the
+// debugger is not connected. Generally this will show up with the application
+// appearing to just hang. This may include the application running from reset
+// or powering up the board (with the application already in FLASH), and also
+// as the application failing to continue to execute after a debug session is
+// terminated.
+//
+// The problem here is that the "bottom layer" of the semihosted variants of
+// the C library, semihosting is implemented by a "BKPT 0xAB" instruction.
+// When the debug tools are not connected, this instruction triggers a hard
+// fault - and the default hard fault handler within an application will
+// typically just contains an infinite loop - causing the application to
+// appear to have hang when no debugger is connected.
+//
+// The below code provides an example hard fault handler which instead looks
+// to see what the instruction that caused the hard fault was - and if it
+// was a "BKPT 0xAB", then it instead returns back to the user application.
+//
+// In most cases this will allow applications containing semihosting
+// operations to execute (to some degree) when the debugger is not connected.
+//
+// == NOTE ==
+//
+// Correct execution of the application containing semihosted operations
+// which are vectored onto this hard fault handler cannot be guaranteed. This
+// is because the handler may not return data or return codes that the higher
+// level C library code or application code expects. This hard fault handler
+// is meant as a development aid, and it is not recommended to leave
+// semihosted code in a production build of your application!
+//
+// ****************************************************************************
+
+// Allow handler to be removed by setting a define (via command line)
+#if !defined (__SEMIHOST_HARDFAULT_DISABLE)
+
+__attribute__((naked))
+void HardFault_Handler(void){
+    __asm(  ".syntax unified\n"
+        // Check which stack is in use
+            "MOVS   R0, #4  \n"
+            "MOV    R1, LR  \n"
+            "TST    R0, R1  \n"
+            "BEQ    _MSP    \n"
+            "MRS    R0, PSP \n"
+            "B  _process      \n"
+            "_MSP:  \n"
+            "MRS    R0, MSP \n"
+        // Load the instruction that triggered hard fault
+        "_process:     \n"
+            "LDR    R1,[R0,#24] \n"
+            "LDRH    R2,[r1] \n"
+        // Semihosting instruction is "BKPT 0xAB" (0xBEAB)
+            "LDR    R3,=0xBEAB \n"
+            "CMP     R2,R3 \n"
+            "BEQ    _semihost_return \n"
+        // Wasn't semihosting instruction so enter infinite loop
+            "B . \n"
+        // Was semihosting instruction, so adjust location to
+        // return to by 1 instruction (2 bytes), then exit function
+        "_semihost_return: \n"
+            "ADDS    R1,#2 \n"
+            "STR    R1,[R0,#24] \n"
+    	// Set a return value from semihosting operation.
+    	// 32 is slightly arbitrary, but appears to allow most
+    	// C Library IO functions sitting on top of semihosting to
+    	// continue to operate to some degree
+    		    "MOVS   R1,#32 \n"
+    		    "STR R1,[ R0,#0 ] \n" // R0 is at location 0 on stack
+    	// Return from hard fault handler to application
+            "BX LR \n"
+        ".syntax divided\n") ;
+}
+
+#endif
+