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cpu: remove CPU_FLAGS_HALT (and flag variable from struct cpu_state).

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we can get handle cpu halts without this flag. CPU's dont actually have these. exceptions are actually implemented as interrupts in real hardware.
This commit is contained in:
Henrik Hautakoski 2019-04-26 13:32:57 +02:00
parent 76a72e6857
commit 0a58a7857f
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GPG key ID: 839F3A7EAFAEAFAA
2 changed files with 6 additions and 18 deletions
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19
vm/cpu.c
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@ -84,7 +84,7 @@ static void execute(struct cpu_state *state, struct instr *instr) {
break; break;
default : default :
fprintf(stderr, "Invalid instruction (%.2X)\n", instr->opcode); fprintf(stderr, "Invalid instruction (%.2X)\n", instr->opcode);
state->flags |= CPU_FLAGS_HALT; state->pc = state->instr_cnt;
break; break;
} }
} }
@ -92,7 +92,6 @@ static void execute(struct cpu_state *state, struct instr *instr) {
void cpu_init(struct cpu_state *state) void cpu_init(struct cpu_state *state)
{ {
state->pc = 0; state->pc = 0;
state->flags = 0;
memset(state->reg, 0, sizeof(state->reg[0]) * CPU_NUM_REGS); memset(state->reg, 0, sizeof(state->reg[0]) * CPU_NUM_REGS);
state->instr_mem = NULL; state->instr_mem = NULL;
@ -119,19 +118,13 @@ void cpu_instr_unload(struct cpu_state *state) {
void cpu_set_pc(struct cpu_state *state, uint16_t addr) { void cpu_set_pc(struct cpu_state *state, uint16_t addr) {
if (addr > state->instr_cnt / 2) { if (addr > state->instr_cnt / 2)
fprintf(stderr, "Runtime error: Invalid instruction address %ui\n", addr); fprintf(stderr, "Runtime error: Invalid instruction address %ui\n", addr);
state->flags |= CPU_FLAGS_HALT;
return;
}
state->pc = addr; state->pc = addr;
} }
static unsigned char* instr_fetch(struct cpu_state *state) { static unsigned char* instr_fetch(struct cpu_state *state) {
if (state->pc + 1 >= state->instr_cnt >> 1)
state->flags |= CPU_FLAGS_HALT;
return state->instr_mem + (state->pc++ << 1); return state->instr_mem + (state->pc++ << 1);
} }
@ -140,13 +133,13 @@ int cpu_tick(struct cpu_state *state) {
struct instr instr; struct instr instr;
unsigned char* next; unsigned char* next;
if (state->flags & CPU_FLAGS_HALT) {
return 1;
}
// Fetch next instruction // Fetch next instruction
next = instr_fetch(state); next = instr_fetch(state);
// We abort if we move past the last program address.
if (state->pc > state->instr_cnt >> 1)
return 1;
// decode instruction. // decode instruction.
instr_decode(next, &instr); instr_decode(next, &instr);

5
vm/cpu.h
View file

@ -25,8 +25,6 @@
#define CPU_NUM_REGS 16 #define CPU_NUM_REGS 16
#define CPU_FLAGS_HALT (1<<0)
struct cpu_state { struct cpu_state {
// Registers r0, r15 // Registers r0, r15
int16_t reg[CPU_NUM_REGS]; int16_t reg[CPU_NUM_REGS];
@ -34,9 +32,6 @@ struct cpu_state {
// Program counter // Program counter
uint16_t pc; uint16_t pc;
// flags
unsigned char flags;
// Instruction // Instruction
unsigned char *instr_mem; unsigned char *instr_mem;
unsigned long instr_cnt; unsigned long instr_cnt;