add simplest I2C on G070 (next will be through DMA)

G0:G070/i2c/usart.h

@@ -0,0 +1,30 @@
+/*
+ * This file is part of the usart 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
+
+#define UARTBUFSZ   (64)
+
+#define USND(t)  do{usart3_sendstr(t);}while(0)
+
+void usart3_setup();
+int usart3_send_blocking(const char *str, int len);
+int usart3_send(const char *str, int len);
+void usart3_sendbuf();
+char *usart3_getline(int *wasbo);
+int usart3_sendstr(const char *str);