USB CDC on STM32G0B1 works

snippets/USB_CDC_ringbuffer/usart.h

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+/*
+ * This file is part of the test project.
+ * Copyright 2026 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 USARTTXBUFSZ    (4096)
+#define USARTRXBUFSZ    (128)
+#define USARTTXDMABUFSZ (1024)
+
+// blocking timeout - not more than 5ms
+#define USARTBLKTMOUT   (5)
+// send buffer each 10ms
+#define USARTSENDTMOUT  (10)
+
+typedef union{
+    struct{
+        uint8_t txerr   : 1; // transmit error
+        uint8_t rxovrfl : 1; // receive buffer overflow
+    };
+    uint8_t all;
+} USART_flags_t;
+
+void usart_setup(uint32_t speed);
+int usart_send(const char *str, int len);
+char *usart_getline();
+int usart_sendstr(const char *str);
+USART_flags_t usart_process();