add rp6502 target

libsrc/rp6502/read.c

@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2023 Rumbledethumps
+ *
+ * SPDX-License-Identifier: Zlib
+ * SPDX-License-Identifier: BSD-3-Clause
+ * SPDX-License-Identifier: Unlicense
+ */
+
+#include <rp6502.h>
+#include <unistd.h>
+
+int __fastcall__ read(int fildes, void *buf, unsigned count)
+{
+    int total = 0;
+    while (count)
+    {
+        unsigned blockcount = (count > 256) ? 256 : count;
+        int bytes_read = read_xstack(&((char *)buf)[total], blockcount, fildes);
+        if (bytes_read < 0)
+        {
+            return bytes_read;
+        }
+        total += bytes_read;
+        count -= bytes_read;
+        if (bytes_read < blockcount)
+        {
+            break;
+        }
+    }
+    return total;
+}