99 lines
4.3 KiB
C
99 lines
4.3 KiB
C
// ****************************************************************************
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// semihost_hardfault.c
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// - Provides hard fault handler to allow semihosting code not
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// to hang application when debugger not connected.
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//
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// ****************************************************************************
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// Copyright 2017-2023 NXP
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// All rights reserved.
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//
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// NXP Confidential. This software is owned or controlled by NXP and may only be
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// used strictly in accordance with the applicable license terms.
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//
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// By expressly accepting such terms or by downloading, installing, activating
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// and/or otherwise using the software, you are agreeing that you have read, and
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// that you agree to comply with and are bound by, such license terms.
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//
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// If you do not agree to be bound by the applicable license terms, then you may not
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// retain, install, activate or otherwise use the software.
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// ****************************************************************************
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//
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// ===== DESCRIPTION =====
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//
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// One of the issues with applications that make use of semihosting operations
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// (such as printf calls) is that the code will not execute correctly when the
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// debugger is not connected. Generally this will show up with the application
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// appearing to just hang. This may include the application running from reset
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// or powering up the board (with the application already in FLASH), and also
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// as the application failing to continue to execute after a debug session is
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// terminated.
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//
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// The problem here is that the "bottom layer" of the semihosted variants of
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// the C library, semihosting is implemented by a "BKPT 0xAB" instruction.
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// When the debug tools are not connected, this instruction triggers a hard
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// fault - and the default hard fault handler within an application will
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// typically just contains an infinite loop - causing the application to
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// appear to have hang when no debugger is connected.
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//
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// The below code provides an example hard fault handler which instead looks
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// to see what the instruction that caused the hard fault was - and if it
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// was a "BKPT 0xAB", then it instead returns back to the user application.
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//
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// In most cases this will allow applications containing semihosting
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// operations to execute (to some degree) when the debugger is not connected.
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//
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// == NOTE ==
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//
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// Correct execution of the application containing semihosted operations
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// which are vectored onto this hard fault handler cannot be guaranteed. This
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// is because the handler may not return data or return codes that the higher
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// level C library code or application code expects. This hard fault handler
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// is meant as a development aid, and it is not recommended to leave
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// semihosted code in a production build of your application!
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//
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// ****************************************************************************
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// Allow handler to be removed by setting a define (via command line)
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#if !defined (__SEMIHOST_HARDFAULT_DISABLE)
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__attribute__((naked))
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void HardFault_Handler(void){
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__asm( ".syntax unified\n"
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// Check which stack is in use
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"MOVS R0, #4 \n"
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"MOV R1, LR \n"
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"TST R0, R1 \n"
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"BEQ _MSP \n"
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"MRS R0, PSP \n"
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"B _process \n"
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"_MSP: \n"
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"MRS R0, MSP \n"
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// Load the instruction that triggered hard fault
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"_process: \n"
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"LDR R1,[R0,#24] \n"
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"LDRH R2,[r1] \n"
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// Semihosting instruction is "BKPT 0xAB" (0xBEAB)
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"LDR R3,=0xBEAB \n"
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"CMP R2,R3 \n"
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"BEQ _semihost_return \n"
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// Wasn't semihosting instruction so enter infinite loop
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"B . \n"
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// Was semihosting instruction, so adjust location to
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// return to by 1 instruction (2 bytes), then exit function
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"_semihost_return: \n"
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"ADDS R1,#2 \n"
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"STR R1,[R0,#24] \n"
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// Set a return value from semihosting operation.
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// 32 is slightly arbitrary, but appears to allow most
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// C Library IO functions sitting on top of semihosting to
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// continue to operate to some degree
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"MOVS R1,#32 \n"
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"STR R1,[ R0,#0 ] \n" // R0 is at location 0 on stack
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// Return from hard fault handler to application
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"BX LR \n"
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".syntax divided\n") ;
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}
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#endif
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