add eeprom flash emulation for G0

G0:G070/flash/flash.h

@@ -0,0 +1,38 @@
+/*
+ * This file is part of the flash project.
+ * Copyright 2023 Edward V. Emelianov <edward.emelianoff@gmail.com>.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+/*
+ * struct to save user configurations
+ */
+typedef struct __attribute__((packed, aligned(8))){
+    uint16_t userconf_sz;           // "magick number"
+    uint16_t flagU16;
+    uint32_t flagU32;
+    char str[32];
+} user_conf;
+
+extern user_conf the_conf; // global user config (read from FLASH to RAM)
+// data from ld-file: start address of storage
+
+void flashstorage_init();
+int store_userconf();
+void dump_userconf();
+int erase_storage();
+