2 files changed, 106 insertions, 0 deletions
diff --git a/core/atas.c b/core/atas.c
new file mode 100644
index 0000000..9585a26
--- /dev/null
+++ b/core/atas.c
@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2026, Apollo Telephone Laboratories.
+ * Provided under the BSD-3 clause.
+ */
+
+#include <stdio.h>
+#include <unistd.h>
+#include "atas/state.h"
+
+/*
+ * Display help options
+ */
+static void
+help(void)
+{
+    printf("-- AT ISA assembler --\n");
+    printf("usage: ./atas [flags] [input file]\n");
+    printf("[-h]    Display this help menu\n");
+}
+
+/*
+ * Begin assembling a specified input file
+ *
+ * @in_file:   Path to input file to assemble
+ */
+static void
+atas_assemble(const char *in_file)
+{
+    struct atas_state state;
+    int error;
+
+    if (in_file == NULL) {
+        return;
+    }
+
+    error = atas_state_init(in_file, &state);
+    if (error < 0) {
+        perror("atas_state_init");
+        return;
+    }
+
+    atas_state_destroy(&state);
+}
+
+int
+main(int argc, char **argv)
+{
+    const char *in_path;
+    int opt;
+
+    if (argc < 2) {
+        printf("fatal: too few arguments\n");
+        return -1;
+    }
+
+    while ((opt = getopt(argc, argv, "hv")) != -1) {
+        switch (opt) {
+        case 'h':
+            help();
+            return 0;
+        }
+    }
+
+    if (optind == argc) {
+        printf("fatal: expected input file\n");
+        return -1;
+    }
+
+    in_path = argv[optind];
+    atas_assemble(in_path);
+    return 0;
+}
diff --git a/core/state.c b/core/state.c
new file mode 100644
index 0000000..8c3dea1
--- /dev/null
+++ b/core/state.c
@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2026, Apollo Telephone Laboratories.
+ * Provided under the BSD-3 clause.
+ */
+
+#include <atas/state.h>
+#include <errno.h>
+
+int
+atas_state_init(const char *in_file, struct atas_state *state)
+{
+    if (in_file == NULL || state == NULL) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    state->in_file = fopen(in_file, "r");
+    if (state->in_file == NULL) {
+        return -1;
+    }
+
+    return 0;
+}
+
+void
+atas_state_destroy(struct atas_state *state)
+{
+    if (state == NULL) {
+        return;
+    }
+
+    fclose(state->in_file);
+    state->in_file = NULL;
+}