60 lines
2.0 KiB
C
60 lines
2.0 KiB
C
#include <stdint.h>
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#include <stdlib.h>
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#include <math.h>
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#include "encoding.h"
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#define EBREAK_OPCODE 0x00100073
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#define EBREAK_MCAUSE 0x00000003
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#define SLLI_X0_X0_0X1F_OPCODE 0x01f01013
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#define SRAI_X0_X0_0X07_OPCODE 0x40705013
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int sh_missing_host = 0;
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void trap()
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{
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uint32_t mepc = read_csr(0x341); // Address of trap
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uint32_t mtval = read_csr(0x343); // Instruction value of trap
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uint32_t mcause = read_csr(0x342); // Reason for the trap
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if (mcause == EBREAK_MCAUSE && mtval == EBREAK_OPCODE){
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// This trap was caused by an EBREAK...
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int aligned = ((mepc-4) & 0x0f) == 0;
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if (aligned
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&& *(uint32_t *)mepc == EBREAK_OPCODE
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&& *(uint32_t *)(mepc-4) == SLLI_X0_X0_0X1F_OPCODE
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&& *(uint32_t *)(mepc+4) == SRAI_X0_X0_0X07_OPCODE)
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{
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// The EBREAK was part of the semihosting call. (See semihosting.c)
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//
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// If a debugger were connected, this would have resulted in a CPU halt,
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// and the debugger would have serviced the the semihosting call.
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//
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// However, the semihosting function was called without a debugger being
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// attached. The best course of action is to simply return from the trap
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// and let the semihosting function continue after the call to EBREAK to
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// prevent the CPU from hanging in the trap handler.
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write_csr(mepc, mepc+4);
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// Set a global variable to tell the semihosting code the the semihosting
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// call
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// didn't execute on the host.
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sh_missing_host = 1;
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return;
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}
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// EBREAK was not part of a semihosting call. This should not have happened.
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// Hang forever.
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while(1)
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;
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}
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// Trap was issued for another reason than an EBREAK.
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// Replace the code below with whatever trap handler you'd normally use. (e.g. interrupt
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// processing.)
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while(1)
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;
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} |