USB CDC on STM32G0B1 works

snippets/USB_CDC_ringbuffer/hardware.c

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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/>.
+ */
+
+#include "hardware.h"
+
+void gpio_setup(){
+    RCC->IOPENR = RCC_IOPENR_GPIOCEN | RCC_IOPENR_GPIOBEN | RCC_IOPENR_GPIOAEN;
+    // set PC8 as opendrain output, PC0 is pullup input, other as default (AIN)
+    GPIOC->MODER = (0xffffffff & ~(GPIO_MODER_MODE6 | GPIO_MODER_MODE13)) | GPIO_MODER_MODER6_O; // GPIO_MODER_MODER13_I == 0
+    GPIOC->PUPDR = GPIO_PUPDR13_PD; // pull down
+    // USART1: PB6 - Tx (AF0), PB7 - Rx (AF0)
+    GPIOB->MODER = (0xffffffff & ~(GPIO_MODER_MODE6 | GPIO_MODER_MODE7)) | MODER_AF(6) | MODER_AF(7);
+    GPIOB->AFR[0] = 0;
+    // RCC->CCIPR = 0; // default -> sysclk/pclk source
+    // USB: PA11/PA12 - AIN
+    //GPIOA->MODER = (0xffffffff & ~(GPIO_MODER_MODE11 | GPIO_MODER_MODE12)) | MODER_AI(11) | MODER_AI(12);
+}