Copyright (c) 2006 CodeSourcery Inc Copyright (c) 2019 Mentor Graphics The authors hereby grant permission to use, copy, modify, distribute, and license this software and its documentation for any purpose, provided that existing copyright notices are retained in all copies and that this notice is included verbatim in any distributions. No written agreement, license, or royalty fee is required for any of the authorized uses. Modifications to this software may be copyrighted by their authors and need not follow the licensing terms described here, provided that the new terms are clearly indicated on the first page of each file where they apply. m68k Semihosting Protocol ------------------------- The instruction used to trigger a semihosting request depends on the m68k processor variant. On ColdFire, "halt" is used; on other processors (which don't implement "halt"), "bkpt #0" may be used. Additionally, a special code sequence is used to distinguish semihosting requests from other uses of the instruction used to trigger it. The semihosting instruction is immediately preceded by a "nop" aligned to a 4-byte boundary, and followed by an invalid sentinel instruction 0x4e7bf000 ("movec %sp,0"). The debug agent handling the semihosting request must adjust the program counter to skip over the sentinel instruction before continuing execution. Registers d0 and d1 are used to pass parameters to the semihosting call. d0 contains a request code. d1 is typically a pointer to a 4-longword parameter block, except for the exit and simulator initialization operations where it is an immediate integer value. The result of the operation is returned in the first word of the parameter block. The second word is used to return an errno value, encoded per the "Errno Values" section of the RSP documentation in the GDB User Manual. The supported d0 request codes are: #define HOSTED_EXIT 0 Terminate program execution; send a 'W' stop reply to GDB. d1 contains the exit code, as an immediate integer rather than indirectly in a parameter block. This semihosting request isn't expected to return. #define HOSTED_INIT_SIM 1 Do simulator initialization, such as allocation of memory for the stack and heap. This semihosting request may be triggered from startup code (crt0.S). On entry to the semihosting request, d1 contains the default initial stack pointer as an immediate value, typically the high end of memory defined by the linker script. If the simulator needs to dynamically allocate memory for the stack, it should set both d1 and sp (a7) to the new stack pointer value. #define HOSTED_OPEN 2 Open file; 'Fopen' GDB fileio request. d1 points to a parameter block containing: [0] pointer to filename [1] filename length [2] open flags, encoded per the GDB RSP documentation [3] mode, encoded per the GDB RSP documentation Return values in parameter block: [0] file descriptor or -1 on error [1] errno, encoded per the GDB RSP documentation #define HOSTED_CLOSE 3 Close file; 'Fclose' GDB fileio request. d1 points to a parameter block containing: [0] file descriptor Return values in parameter block: [0] return status [1] errno, encoded per the GDB RSP documentation #define HOSTED_READ 4 Read from file; 'Fread' GDB fileio request. d1 points to a parameter block containing: [0] file descriptor [1] pointer to buffer [2] buffer size Return values in parameter block: [0] number of bytes read [1] errno, encoded per the GDB RSP documentation #define HOSTED_WRITE 5 Write to file; 'Fwrite' GDB fileio request. d1 points to a parameter block containing: [0] file descriptor [1] pointer to buffer [2] byte count Return values in parameter block: [0] number of bytes written [1] errno, encoded per the GDB RSP documentation #define HOSTED_LSEEK 6 File seek; 'Flseek' GDB fileio request. d1 points to a parameter block containing: [0] file descriptor [1] high word of 64-bit offset [2] low word of 64-bit offset [3] seek flag, encoded per the GDB RSP documentation Return values in parameter block: [0] high word of 64-bit result [1] low word of 64-bit result [2] errno, encoded per the GDB RSP documentation #define HOSTED_RENAME 7 File rename; 'Frename' GDB fileio request. d1 points to a parameter block containing: [0] oldname pointer [1] oldname length [2] newname pointer [3] newname length Return values in parameter block: [0] return status [1] errno, encoded per the GDB RSP documentation #define HOSTED_UNLINK 8 File unlink/delete; 'Funlink' GDB fileio request. d1 points to a parameter block containing: [0] filename pointer [1] filename length Return values in parameter block: [0] return status [1] errno, encoded per the GDB RSP documentation #define HOSTED_STAT 9 File information; 'Fstat' GDB fileio request. d1 points to a parameter block containing: [0] filename pointer [1] filename length [2] pointer to stat buf, using the structure definition in the GDB RSP documentation Return values in parameter block: [0] return status [1] errno, encoded per the GDB RSP documentation #define HOSTED_FSTAT 10 File information; 'Ffstat' GDB fileio request. d1 points to a parameter block containing: [0] file descriptor [1] pointer to stat buf, using the structure definition in the GDB RSP documentation Return values in parameter block: [0] return status [1] errno, encoded per the GDB RSP documentation #define HOSTED_GETTIMEOFDAY 11 Get current time; 'Fgettimeofday' GDB fileio request. d1 points to a parameter block containing: [0] timeval pointer, using the structure definition in the GDB RSP documentation Return values in parameter block: [0] return status [1] errno, encoded per the GDB RSP documentation #define HOSTED_ISATTY 12 Return true if the file descriptor is the GDB console; 'Fisatty' GDB fileio request. d1 points to a parameter block containing: [0] file descriptor Return values in parameter block: [0] return status [1] errno, encoded per the GDB RSP documentation #define HOSTED_SYSTEM 13 System call; 'Fsystem' GDB fileio request. d1 points to a parameter block containing: [0] command pointer [1] command length Return values in parameter block: [0] return status [1] errno, encoded per the GDB RSP documentation