emux64: cpu: Add initial CPU cycle loop w/ HLT

Signed-off-by: Ian Moffett <ian@osmora.org>

4 files changed, 117 insertions, 5 deletions

diff --git a/emux64/src/cpu/cpu_cycle.c b/emux64/src/cpu/cpu_cycle.c
new file mode 100644
index 0000000..ef0cc24
--- /dev/null
+++ b/emux64/src/cpu/cpu_cycle.c
@@ -0,0 +1,102 @@
+/*
+ * Copyright (c) 2025 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <stdio.h>
+#include <errno.h>
+#include "rom.h"
+#include "cpu/cpu.h"
+
+/*
+ * Fetch an instruction byte from memory
+ *
+ * @core: Core to fetch for
+ * @byte_res: Result is written here
+ *
+ * XXX: Caller is to increment `core->pc'
+ *
+ * Returns zero on success
+ */
+static int
+cpu_fetch(struct osmx_core *core, uint8_t *byte_res)
+{
+    uint8_t *rom;
+    size_t rom_len;
+
+    if (core == NULL || byte_res == NULL) {
+        printf("fatal: bad arg in %s()\n", __func__);
+        return -1;
+    }
+
+    if ((rom = g_firmware.buf) == NULL) {
+        printf("fatal: ROM is uninitialized\n");
+        return -1;
+    }
+
+    rom_len = g_firmware.length;
+    if (core->pc >= (CPU_BUA_PBASE + rom_len)) {
+        printf("fatal: PC outside of ROM\n");
+        return -1;
+    }
+
+    if (core->pc >= CPU_BUA_PBASE) {
+        *byte_res = rom[core->pc - CPU_BUA_PBASE];
+    }
+
+    return 0;
+}
+
+int
+cpu_run(struct osmx_core *core)
+{
+    uint8_t opcode;
+    int error;
+
+    if (core == NULL) {
+        return -EINVAL;
+    }
+
+    core->run = 1;
+    while (core->run) {
+        error = cpu_fetch(core, &opcode);
+        if (error < 0) {
+            core->run = 0;
+            break;
+        }
+
+        /* Test opcode cases */
+        switch (opcode) {
+        case OP_HLT:
+            printf("** HALTED **\n");
+            core->run = false;
+            continue;
+        }
+
+        ++core->pc;
+    }
+}
diff --git a/emux64/src/include/cpu/cpu.h b/emux64/src/include/cpu/cpu.h
index 2d35c73..bffb6c0 100644
--- a/emux64/src/include/cpu/cpu.h
+++ b/emux64/src/include/cpu/cpu.h
@@ -62,12 +62,14 @@
  * @fn: IEEE 754 single-precision registers
  * @dn: IEEE 754 double-precision registers
  * @pc: Program counter
+ * @run: Processor running
  */
 struct osmx_core {
     uint64_t xn[N_GPREG];
     float fn[N_FLOATREG];
     double dn[N_DUBREG];
     uintptr_t pc;
+    uint8_t run : 1;
 };
 
 /*
@@ -97,4 +99,14 @@ int cpu_reset(struct osmx_core *core);
  */
 void cpu_dump(struct osmx_core *core);
 
+/*
+ * Initialize the registers to use for the
+ * CPU
+ *
+ * @core: Core to use
+ *
+ * Returns zero on success
+ */
+int cpu_run(struct osmx_core *core);
+
 #endif  /* !CPU_CPU_H */
diff --git a/emux64/src/include/rom.h b/emux64/src/include/rom.h
index 8d3501c..0480440 100644
--- a/emux64/src/include/rom.h
+++ b/emux64/src/include/rom.h
@@ -44,6 +44,8 @@ struct osmx_rom {
     size_t length;
 };
 
+extern struct osmx_rom g_firmware;
+
 /*
  * Open a ROM file by path
  *
diff --git a/emux64/src/main.c b/emux64/src/main.c
index 8c42655..b8d39b4 100644
--- a/emux64/src/main.c
+++ b/emux64/src/main.c
@@ -74,11 +74,7 @@ run(struct osmx_core *core)
         return error;
     }
 
-    printf("ROM: ");
-    for (int i = 0; i < g_firmware.length; ++i) {
-        printf("%02X ", g_firmware.buf[i]);
-    }
-    printf("\n");
+    cpu_run(core);
 }
 
 int