ubs-serial-rs485: First solidly working version.

Needs major refactoring to split out the _actual_ arch dependent pieces.
Needs parity and more complete baud rate support.
Needs rs485 support.

tests/usb-serial-rs485/Makefile.stm32f4-disco

@@ -0,0 +1,38 @@
+##
+## This file is part of the libopencm3 project.
+##
+## This library is free software: you can redistribute it and/or modify
+## it under the terms of the GNU Lesser General Public License as published by
+## the Free Software Foundation, either version 3 of the License, or
+## (at your option) any later version.
+##
+## This library 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 Lesser General Public License for more details.
+##
+## You should have received a copy of the GNU Lesser General Public License
+## along with this library.  If not, see <http://www.gnu.org/licenses/>.
+##
+
+BOARD = stm32f4-disco
+PROJECT = usb-serial-rs485-$(BOARD)
+BUILD_DIR = bin-$(BOARD)
+
+SHARED_DIR = ../../shared
+
+CFILES = main-$(BOARD).c
+CFILES += usb_cdcacm.c usb_cdcacm-arch.c
+CFILES += ringb.c
+CFILES += trace.c trace_stdio.c
+
+VPATH += $(SHARED_DIR)
+INCLUDES += $(patsubst %,-I%, . $(SHARED_DIR))
+OPENCM3_DIR=../../libopencm3
+
+# Copy this to some arch shared?
+DEVICE=stm32f405xg
+OOCD_FILE= ../../openocd/openocd.stm32f4-disco.cfg
+
+include ../../rules.mk
+

tests/usb-serial-rs485/README

@@ -0,0 +1,21 @@
+------------------------------------------------------------------------------
+README
+------------------------------------------------------------------------------
+
+This implements a USB CDC-ACM device, connected to USART2 (PA2-tx/PA3-rx)
+An interrupt driven tx ring buffer is used for usb->serial, and a similar
+interrupt driven rx ring buffer is used for serial->usb.
+Baud rates from 2400-460800 are tested with zmodem transfers in both directions.
+
+Parity not yet finished, and baudrates below 1200 need fiddling with clock prescalers.
+When it's finished, rs485 support should be available via the TC interrupt.
+
+A GPIO is toggled around USART transmissions to control an RS485 line
+transceiver, following ST's app note. The RS485 driver enable line is,
+by default, just the onboard red LEDs.
+
+The orange/blue LEDs indicate tx/rx activity, but especially for the rx line,
+you won't really see it without heavy data rates.
+
+This example is heavily based on the existing usb_cdcacm and usart demos.
+

tests/usb-serial-rs485/main-stm32f4-disco.c

@@ -0,0 +1,169 @@
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2014 Karl Palsson <karlp@tweak.net.au>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <libopencm3/cm3/nvic.h>
+#include <libopencm3/stm32/gpio.h>
+#include <libopencm3/stm32/rcc.h>
+#include <libopencm3/stm32/usart.h>
+
+#include <stdio.h>
+#include "syscfg.h"
+#include "usb_cdcacm.h"
+#include "ringb.h"
+#include "trace.h"
+
+#define ER_DEBUG
+#ifdef ER_DEBUG
+#define ER_DPRINTF(fmt, ...) \
+    do { printf(fmt, ## __VA_ARGS__); } while (0)
+#else
+#define ER_DPRINTF(fmt, ...) \
+    do { } while (0)
+#endif
+
+
+static usbd_device *usbd_dev;
+static struct ringb rx_ring;
+static uint8_t rx_ring_data[64];
+struct ringb tx_ring;
+static uint8_t tx_ring_data[128];
+bool nakked = false;
+
+static void usart_setup(void)
+{
+	/* Enable the USART2 interrupt. */
+	nvic_enable_irq(NVIC_USART2_IRQ);
+
+	/* USART2 pins are on port A */
+	rcc_periph_clock_enable(RCC_GPIOA);
+	gpio_mode_setup(GPIOA, GPIO_MODE_AF, GPIO_PUPD_NONE, GPIO2 | GPIO3);
+	gpio_set_af(GPIOA, GPIO_AF7, GPIO2 | GPIO3);
+
+	/* Enable clocks for USART2. */
+	rcc_periph_clock_enable(RCC_USART2);
+
+	/* Setup USART2 parameters. */
+	usart_set_baudrate(USART2, 115200);
+	usart_set_databits(USART2, 8);
+	usart_set_stopbits(USART2, USART_STOPBITS_1);
+	usart_set_mode(USART2, USART_MODE_TX_RX);
+	usart_set_parity(USART2, USART_PARITY_NONE);
+	usart_set_flow_control(USART2, USART_FLOWCONTROL_NONE);
+
+	/* Enable USART2 Receive interrupt. */
+	usart_enable_rx_interrupt(USART2);
+
+	/* Finally enable the USART. */
+	usart_enable(USART2);
+}
+
+void usart2_isr(void)
+{
+	// usbser-rxne()
+	/* Check if we were called because of RXNE. */
+	if (usart_get_interrupt_source(USART2, USART_SR_RXNE)) {
+		gpio_set(LED_RX_PORT, LED_RX_PIN);
+		uint8_t c = usart_recv(USART2);
+		if (ringb_put(&rx_ring, c)) {
+			// good,
+		} else {
+			// fatal, you should always have drained by now.
+			// (when you've got it all ironed out, _actually_
+			// just drop and count drops), but not yet...
+			ER_DPRINTF("rx buffer full\n");
+			while(1);
+		}
+		gpio_clear(LED_RX_PORT, LED_RX_PIN);
+	}
+	// usbser-irq-txe()
+	if (usart_get_interrupt_source(USART2, USART_SR_TXE)) {
+		if (ringb_depth(&tx_ring) == 0) {
+			// turn off tx empty interrupts, nothing left to send
+			usart_disable_tx_interrupt(USART2);
+			ER_DPRINTF("OFF\n");
+			// Turn on tx complete interrupts, for rs485 de
+//			USART_CR1(USART2) |= ~USART_CR1_TCIE;
+		} else {
+			int c = ringb_get(&tx_ring);
+			usart_send(USART2, c);
+		}
+	}
+	// usbser-irq-txc?  rs485 is auto on some devices, but can be emulated anyway
+//	if (usart_get_interrupt_source(USART2, USART_SR_TC)) {
+//		ER_DPRINTF("TC");
+//		// turn off the complete irqs, we're done now.
+//		USART_SR(USART2) &= ~USART_SR_TC;
+//		USART_CR1(USART2) &= ~USART_CR1_TCIE;
+//		gpio_clear(LED_TX_PORT, LED_TX_PIN);
+//		gpio_clear(RS485DE_PORT, RS485DE_PIN);
+//	}
+}
+
+/* Y0, moron, nothing's stopping rx irqs from happening, have fun when you overflow temp buffer! */
+static void task_drain_rx(struct ringb *r) {
+	uint8_t zero_copy_is_for_losers[sizeof(rx_ring_data)];
+	int zci = 0;
+	int c = ringb_get(r);
+	while (c >= 0) {
+		zero_copy_is_for_losers[zci++] = c;
+		c = ringb_get(r);
+	}
+	if (zci) {
+		trace_send16(STIMULUS_RING_DRAIN, zci);
+		glue_data_received_cb(zero_copy_is_for_losers, zci);
+	}
+
+}
+
+int main(void)
+{
+	rcc_clock_setup_hse_3v3(&rcc_hse_8mhz_3v3[RCC_CLOCK_3V3_168MHZ]);
+	ER_DPRINTF("And we're alive!\n");
+	/* Leds and rs485 are on port D */
+	rcc_periph_clock_enable(RCC_GPIOD);
+	gpio_mode_setup(LED_RX_PORT, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE,
+		LED_RX_PIN | LED_TX_PIN);
+	gpio_mode_setup(RS485DE_PORT, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE,
+		RS485DE_PIN);
+
+	usart_setup();
+	ringb_init(&rx_ring, rx_ring_data, sizeof(rx_ring_data));
+	ringb_init(&tx_ring, tx_ring_data, sizeof(tx_ring_data));
+
+	usb_cdcacm_init(&usbd_dev);
+
+	ER_DPRINTF("Looping...\n");
+	volatile int i = 0;
+	while (1) {
+		usbd_poll(usbd_dev);
+		if (i++ > 500) {
+			// hacktastic
+			if (ringb_depth(&tx_ring) < 64 && nakked) {
+				usbd_ep_nak_set(usbd_dev, 1, 0);
+				nakked = false;
+			}
+
+			task_drain_rx(&rx_ring);
+			i = 0;
+		}
+
+	}
+
+}
+

tests/usb-serial-rs485/ringb.c

@@ -0,0 +1,59 @@
+
+#include "ringb.h"
+void ringb_init(struct ringb *ring, uint8_t *buf, int len)
+{
+	ring->buf_len = len;
+	ring->buf = buf;
+	ring->idx_r = 0;
+	ring->idx_w = 0;
+}
+
+int ringb_get(struct ringb *ring) {
+#if 1
+	int rval;
+	if (ring->idx_r != ring->idx_w) {
+		rval = ring->buf[ring->idx_r];
+		ring->idx_r = (ring->idx_r + 1) % ring->buf_len;
+		return rval;
+	}
+	return -1;
+#else
+	if (((ring->idx_w - ring->idx_r) % ring->buf_len) >= 0) {
+		int rval = ring->buf[ring->idx_r];
+		ring->idx_r = (ring->idx_r + 1) % ring->buf_len;
+		return rval;
+	} else {
+		return -1;
+	}
+#endif
+}
+
+bool ringb_put(struct ringb *ring, uint8_t c) {
+#if 1
+	unsigned int next = (ring->idx_w + 1) % ring->buf_len;
+	if (next != ring->idx_r) {
+		ring->buf[ring->idx_w] = c;
+		ring->idx_w = next;
+		return true;
+	}
+	return false;
+#else
+	if (((ring->idx_w - ring->idx_r) % ring->buf_len) == 0) {
+		return false;
+	}
+	ring->buf[ring->idx_w] = c;
+	ring->idx_w = (ring->idx_w + 1) % ring->buf_len;
+	return true;
+#endif
+	
+}
+
+
+void ringb_flush(struct ringb *ring) {
+	ring->idx_r = 0;
+	ring->idx_w = 0;
+}
+
+int ringb_depth(struct ringb *ring) {
+	return ((unsigned int)(ring->idx_w - ring->idx_r) % ring->buf_len);
+}

tests/usb-serial-rs485/ringb.h

@@ -0,0 +1,60 @@
+/*
+ * Karl Palsson <karlp@tweak.net.au>
+ * Considered to be released under your choice of:
+ * MIT/ISC/Apache2/BSD2Clause/GPLv2
+ * If you're looking for elegant compact performance you've come to the wrong
+ * place hombre.
+ */
+
+#pragma once
+
+#ifdef	__cplusplus
+extern "C" {
+#endif
+
+#include <stdbool.h>
+#include <stdint.h>
+
+struct ringb {
+	volatile unsigned int idx_r;
+	volatile unsigned int idx_w;
+	uint8_t *buf;
+	int buf_len;
+};
+
+/**
+ * Load up a ring buffer. Always suceeds
+ * @param ring struct saving state, provided by the user
+ * @param buf where the data will be kept
+ * @param len size of buf in in elements.
+ */
+void ringb_init(struct ringb *ring, uint8_t *buf, int len);
+
+/**
+ * push data in
+ * @param ring
+ * @param c
+ * @return true if space was available
+ */
+bool ringb_put(struct ringb *ring, uint8_t c);
+
+/**
+ * pull data out
+ * @param ring
+ * @return -1 for no data, uint8_t range for valid.
+ */
+int ringb_get(struct ringb *ring);
+
+/**
+ * Toss data and reset to empty
+ * @param ring
+ */
+void ringb_flush(struct ringb *ring);
+
+int ringb_depth(struct ringb *ring);
+
+
+
+#ifdef	__cplusplus
+}
+#endif

tests/usb-serial-rs485/syscfg.h

@@ -0,0 +1,50 @@
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2014 Karl Palsson <karlp@tweak.net.au>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef SYSCFG_H
+#define	SYSCFG_H
+
+#ifdef	__cplusplus
+extern "C" {
+#endif
+
+/* TODO: should really make a stm32f4discovery.h file... */
+
+#define LED_RX_PORT	GPIOD
+#define LED_RX_PIN	GPIO15  /* Blue, but you won't see this one much */
+#define LED_TX_PORT	GPIOD
+#define LED_TX_PIN	GPIO13  /* orange */
+/* On stm32f4 discovery, this is actually another led... */
+#define RS485DE_PORT	GPIOD
+#define RS485DE_PIN	GPIO14  /* red */
+
+#define STREAM_USART2_TX 6
+
+#define STIMULUS_RING_DRAIN 2
+#define STIMULUS_RING_PUSH 3
+#define STIMULUS_TXC 4
+#define STIMULUS_TX 5
+
+
+#ifdef	__cplusplus
+}
+#endif
+
+#endif	/* SYSCFG_H */
+

tests/usb-serial-rs485/usb_cdcacm-arch.c

@@ -0,0 +1,124 @@
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2014 Karl Palsson <karlp@tweak.net.au>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <libopencm3/cm3/nvic.h>
+#include <libopencm3/stm32/dma.h>
+#include <libopencm3/stm32/gpio.h>
+#include <libopencm3/stm32/rcc.h>
+#include <libopencm3/stm32/usart.h>
+
+#include "usb_cdcacm.h"
+#include "syscfg.h"
+#include "ringb.h"
+
+extern bool out_in_progress;
+
+void usb_cdcacm_setup_pre_arch(void)
+{
+	rcc_periph_clock_enable(RCC_GPIOA);
+	rcc_periph_clock_enable(RCC_OTGFS);
+
+	gpio_mode_setup(GPIOA, GPIO_MODE_AF, GPIO_PUPD_NONE,
+		GPIO9 | GPIO11 | GPIO12);
+	gpio_set_af(GPIOA, GPIO_AF10, GPIO9 | GPIO11 | GPIO12);
+
+}
+
+void usb_cdcacm_setup_post_arch(void)
+{
+}
+
+// hacktastic
+extern struct ringb tx_ring;
+void glue_send_data_cb(uint8_t *buf, uint16_t len)
+{
+	if (len == 0) {
+		return;
+	}
+	gpio_set(LED_TX_PORT, LED_TX_PIN);
+	gpio_set(RS485DE_PORT, RS485DE_PIN);
+	for (int x = 0; x < len; x++) {
+		if (!ringb_put(&tx_ring, buf[x])) {
+			// failed to process usb traffic properly.
+			// should _never_ happen, means we failed to nak in time.
+			// this is _never_recoverable beyond watchdog reset.
+			while(1);
+		}
+		usart_enable_tx_interrupt(USART2);
+	}
+}
+
+void glue_set_line_state_cb(uint8_t dtr, uint8_t rts)
+{
+	(void) dtr;
+	(void) rts;
+	// LM4f has an implementation of this if you're keen
+}
+
+int glue_set_line_coding_cb(uint32_t baud, uint8_t databits,
+	enum usb_cdc_line_coding_bParityType cdc_parity,
+	enum usb_cdc_line_coding_bCharFormat cdc_stopbits)
+{
+	int uart_parity;
+	int uart_stopbits;
+
+	if (databits < 8 || databits > 9) {
+		return 0;
+	}
+
+	/* Be careful here, ST counts parity as a data bit */
+	switch (cdc_parity) {
+	case USB_CDC_NO_PARITY:
+		uart_parity = USART_PARITY_NONE;
+		break;
+	case USB_CDC_ODD_PARITY:
+		uart_parity = USART_PARITY_ODD;
+		databits++;
+		break;
+	case USB_CDC_EVEN_PARITY:
+		uart_parity = USART_PARITY_EVEN;
+		databits++;
+		break;
+	default:
+		return 0;
+	}
+
+	switch (cdc_stopbits) {
+	case USB_CDC_1_STOP_BITS:
+		uart_stopbits = USART_STOPBITS_1;
+		break;
+	case USB_CDC_2_STOP_BITS:
+		uart_stopbits = USART_STOPBITS_2;
+		break;
+	default:
+		return 0;
+	}
+
+	/* Disable the UART while we mess with its settings */
+	usart_disable(USART2);
+	/* Set communication parameters */
+	usart_set_baudrate(USART2, baud);
+	usart_set_databits(USART2, databits);
+	usart_set_parity(USART2, uart_parity);
+	usart_set_stopbits(USART2, uart_stopbits);
+	/* Back to work. */
+	usart_enable(USART2);
+
+	return 1;
+}

tests/usb-serial-rs485/usb_cdcacm.c

@@ -0,0 +1,310 @@
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2010 Gareth McMullin <gareth@blacksphere.co.nz>
+ * Copyright (C) 2013 Alexandru Gagniuc <mr.nuke.me@gmail.com>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+/*
+ * This package is _meant_ to be platform independent, just a full
+ * cdc-acm impl, with callbacks
+ */
+
+#include "usb_cdcacm.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <libopencm3/usb/usbd.h>
+#include <libopencm3/usb/cdc.h>
+#include <libopencm3/cm3/scb.h>
+
+#include "ringb.h"
+
+#define ER_DEBUG
+#ifdef ER_DEBUG
+#define ER_DPRINTF(fmt, ...) \
+    do { printf(fmt, ## __VA_ARGS__); } while (0)
+#else
+#define ER_DPRINTF(fmt, ...) \
+    do { } while (0)
+#endif
+
+
+uint8_t usbd_control_buffer[128];
+usbd_device *acm_dev;
+
+bool out_in_progress;
+
+static const struct usb_device_descriptor dev = {
+	.bLength = USB_DT_DEVICE_SIZE,
+	.bDescriptorType = USB_DT_DEVICE,
+	.bcdUSB = 0x2000,
+	.bDeviceClass = USB_CLASS_CDC,
+	.bDeviceSubClass = 0,
+	.bDeviceProtocol = 0,
+	.bMaxPacketSize0 = 64,
+	.idVendor = 0xc03e,
+	.idProduct = 0xb007,
+	.bcdDevice = 0x2000,
+	.iManufacturer = 1,
+	.iProduct = 2,
+	.iSerialNumber = 3,
+	.bNumConfigurations = 1,
+};
+
+/*
+ * This notification endpoint isn't implemented. According to CDC spec it's
+ * optional, but its absence causes a NULL pointer dereference in the
+ * Linux cdc_acm driver.
+ */
+static const struct usb_endpoint_descriptor comm_endp[] = {{
+	.bLength = USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType = USB_DT_ENDPOINT,
+	.bEndpointAddress = 0x83,
+	.bmAttributes = USB_ENDPOINT_ATTR_INTERRUPT,
+	.wMaxPacketSize = 16,
+	.bInterval = 1,
+}};
+
+static const struct usb_endpoint_descriptor data_endp[] = {{
+	.bLength = USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType = USB_DT_ENDPOINT,
+	.bEndpointAddress = 0x01,
+	.bmAttributes = USB_ENDPOINT_ATTR_BULK,
+	.wMaxPacketSize = 64,
+	.bInterval = 1,
+}, {
+	.bLength = USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType = USB_DT_ENDPOINT,
+	.bEndpointAddress = 0x82,
+	.bmAttributes = USB_ENDPOINT_ATTR_BULK,
+	.wMaxPacketSize = 64,
+	.bInterval = 1,
+}};
+
+static const struct {
+	struct usb_cdc_header_descriptor header;
+	struct usb_cdc_call_management_descriptor call_mgmt;
+	struct usb_cdc_acm_descriptor acm;
+	struct usb_cdc_union_descriptor cdc_union;
+} __attribute__ ((packed)) cdcacm_functional_descriptors = {
+	.header = {
+		.bFunctionLength = sizeof(struct usb_cdc_header_descriptor),
+		.bDescriptorType = CS_INTERFACE,
+		.bDescriptorSubtype = USB_CDC_TYPE_HEADER,
+		.bcdCDC = 0x0110,
+	},
+	.call_mgmt = {
+		.bFunctionLength =
+			sizeof(struct usb_cdc_call_management_descriptor),
+		.bDescriptorType = CS_INTERFACE,
+		.bDescriptorSubtype = USB_CDC_TYPE_CALL_MANAGEMENT,
+		.bmCapabilities = 0,
+		.bDataInterface = 1,
+	},
+	.acm = {
+		.bFunctionLength = sizeof(struct usb_cdc_acm_descriptor),
+		.bDescriptorType = CS_INTERFACE,
+		.bDescriptorSubtype = USB_CDC_TYPE_ACM,
+		.bmCapabilities = (1 << 1),
+	},
+	.cdc_union = {
+		.bFunctionLength = sizeof(struct usb_cdc_union_descriptor),
+		.bDescriptorType = CS_INTERFACE,
+		.bDescriptorSubtype = USB_CDC_TYPE_UNION,
+		.bControlInterface = 0,
+		.bSubordinateInterface0 = 1,
+	}
+};
+
+static const struct usb_interface_descriptor comm_iface[] = {{
+	.bLength = USB_DT_INTERFACE_SIZE,
+	.bDescriptorType = USB_DT_INTERFACE,
+	.bInterfaceNumber = 0,
+	.bAlternateSetting = 0,
+	.bNumEndpoints = 1,
+	.bInterfaceClass = USB_CLASS_CDC,
+	.bInterfaceSubClass = USB_CDC_SUBCLASS_ACM,
+	.bInterfaceProtocol = USB_CDC_PROTOCOL_AT,
+	.iInterface = 0,
+
+	.endpoint = comm_endp,
+
+	.extra = &cdcacm_functional_descriptors,
+	.extralen = sizeof(cdcacm_functional_descriptors)
+}};
+
+static const struct usb_interface_descriptor data_iface[] = {{
+	.bLength = USB_DT_INTERFACE_SIZE,
+	.bDescriptorType = USB_DT_INTERFACE,
+	.bInterfaceNumber = 1,
+	.bAlternateSetting = 0,
+	.bNumEndpoints = 2,
+	.bInterfaceClass = USB_CLASS_DATA,
+	.bInterfaceSubClass = 0,
+	.bInterfaceProtocol = 0,
+	.iInterface = 0,
+
+	.endpoint = data_endp,
+}};
+
+static const struct usb_interface ifaces[] = {{
+	.num_altsetting = 1,
+	.altsetting = comm_iface,
+}, {
+	.num_altsetting = 1,
+	.altsetting = data_iface,
+}};
+
+static const struct usb_config_descriptor config = {
+	.bLength = USB_DT_CONFIGURATION_SIZE,
+	.bDescriptorType = USB_DT_CONFIGURATION,
+	.wTotalLength = 0,
+	.bNumInterfaces = 2,
+	.bConfigurationValue = 1,
+	.iConfiguration = 0,
+	.bmAttributes = 0x80,
+	.bMaxPower = 0x32,
+
+	.interface = ifaces,
+};
+
+static const char *usb_strings[] = {
+	"libopencm3",
+	"usb_to_serial_cdcacm",
+	"none",
+	"DEMO",
+};
+
+static int cdcacm_control_request(usbd_device *usbd_dev,
+	struct usb_setup_data *req, uint8_t **buf,
+	uint16_t *len,
+	void (**complete) (usbd_device *usbd_dev,
+	struct usb_setup_data *
+	req))
+{
+	uint8_t dtr, rts;
+
+	(void) complete;
+	(void) buf;
+	(void) usbd_dev;
+
+	switch (req->bRequest) {
+	case USB_CDC_REQ_SET_CONTROL_LINE_STATE:
+	{
+		/*
+		 * This Linux cdc_acm driver requires this to be implemented
+		 * even though it's optional in the CDC spec, and we don't
+		 * advertise it in the ACM functional descriptor.
+		 */
+
+		dtr = (req->wValue & (1 << 0)) ? 1 : 0;
+		rts = (req->wValue & (1 << 1)) ? 1 : 0;
+		ER_DPRINTF("CTRLRQ: Set Line state: dtr:%d rts: %d\n", dtr, rts);
+
+		glue_set_line_state_cb(dtr, rts);
+
+		return 1;
+	}
+	case USB_CDC_REQ_SET_LINE_CODING:
+	{
+		struct usb_cdc_line_coding *coding;
+
+		if (*len < sizeof (struct usb_cdc_line_coding))
+			return 0;
+
+		coding = (struct usb_cdc_line_coding *) *buf;
+		ER_DPRINTF("CTRLRQ: line coding: %lu(%u:%u:%u)\n", coding->dwDTERate,
+			coding->bDataBits, coding->bParityType, coding->bCharFormat);
+		return glue_set_line_coding_cb(coding->dwDTERate,
+			coding->bDataBits,
+			coding->bParityType,
+			coding->bCharFormat);
+	}
+	}
+	return 0;
+}
+
+extern bool nakked;
+extern struct ringb tx_ring;
+static void cdcacm_data_rx_cb(usbd_device *usbd_dev, uint8_t ep)
+{
+	uint8_t buf[64];
+	/* nak right now, we're not sure whether we'll be able to even process this!*/
+	usbd_ep_nak_set(usbd_dev, ep, 1);
+	int len = usbd_ep_read_packet(usbd_dev, ep, buf, 64);
+	ER_DPRINTF("Hrx%db\n", len);
+	// push all of what we got into our outbound fifo
+	glue_send_data_cb(buf, len);
+	if (ringb_depth(&tx_ring) < 64) {
+		ER_DPRINTF("ACK\n");
+		usbd_ep_nak_set(usbd_dev, ep, 0);
+	} else {
+		nakked = true;
+	}
+}
+
+static void cdcacm_set_config(usbd_device *usbd_dev, uint16_t wValue)
+{
+	(void) wValue;
+
+	usbd_ep_setup(usbd_dev, 0x01, USB_ENDPOINT_ATTR_BULK, 64,
+		cdcacm_data_rx_cb);
+	usbd_ep_setup(usbd_dev, 0x82, USB_ENDPOINT_ATTR_BULK, 64, NULL);
+	usbd_ep_setup(usbd_dev, 0x83, USB_ENDPOINT_ATTR_INTERRUPT, 16, NULL);
+
+	usbd_register_control_callback(usbd_dev,
+		USB_REQ_TYPE_CLASS |
+		USB_REQ_TYPE_INTERFACE,
+		USB_REQ_TYPE_TYPE |
+		USB_REQ_TYPE_RECIPIENT,
+		cdcacm_control_request);
+}
+
+/* FIXME - need to report this! */
+void cdcacm_line_state_changed_cb(uint8_t linemask)
+{
+	const int size = sizeof (struct usb_cdc_notification) + 2;
+	uint8_t buf[size];
+
+	struct usb_cdc_notification *notify = (void *) buf;
+	notify->bmRequestType = 0xa1;
+	notify->bNotification = USB_CDC_NOTIFY_SERIAL_STATE;
+	notify->wValue = 0;
+	notify->wIndex = 1;
+	notify->wLength = 2;
+	uint16_t *data = (void *) &buf[sizeof (struct usb_cdc_notification)];
+	*data = linemask;
+
+	while (usbd_ep_write_packet(acm_dev, 0x83, buf, size) == size);
+}
+
+void glue_data_received_cb(uint8_t *buf, uint16_t len)
+{
+	ER_DPRINTF("Drx %db\n", len);
+	usbd_ep_write_packet(acm_dev, 0x82, buf, len);
+}
+
+void usb_cdcacm_init(usbd_device **usbd_dev)
+{
+	usb_cdcacm_setup_pre_arch();
+
+	*usbd_dev = usbd_init(&otgfs_usb_driver, &dev, &config, usb_strings, 4,
+		usbd_control_buffer, sizeof (usbd_control_buffer));
+	acm_dev = *usbd_dev;
+	usbd_register_set_config_callback(acm_dev, cdcacm_set_config);
+
+	usb_cdcacm_setup_post_arch();
+}

tests/usb-serial-rs485/usb_cdcacm.h

@@ -0,0 +1,56 @@
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2014 Karl Palsson <karlp@tweak.net.au>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+/*
+ * This is the header file for a usb_cdcacm implmentation, usb_cdcacm.c is the
+ * platform independent portion, and usb_cdcacm-arch.c should be re-implemented
+ * for other platforms.
+ */
+
+#ifndef USB_CDCACM_H
+#define	USB_CDCACM_H
+
+#ifdef	__cplusplus
+extern "C" {
+#endif
+
+#include <libopencm3/usb/usbd.h>
+#include <libopencm3/usb/cdc.h>
+
+	void usb_cdcacm_init(usbd_device **usb_dev);
+	void usb_cdcacm_setup_pre_arch(void);
+	void usb_cdcacm_setup_post_arch(void);
+	void cdcacm_send_data(uint8_t *buf, uint16_t len);
+	void cdcacm_line_state_changed_cb(uint8_t linemask);
+
+	/* Call this if you have data to send to the usb host */
+	void glue_data_received_cb(uint8_t *buf, uint16_t len);
+	/* These will be called by usb_cdcacm code */
+	void glue_send_data_cb(uint8_t *buf, uint16_t len);
+
+	void glue_set_line_state_cb(uint8_t dtr, uint8_t rts);
+	int glue_set_line_coding_cb(uint32_t baud, uint8_t databits,
+		enum usb_cdc_line_coding_bParityType cdc_parity,
+		enum usb_cdc_line_coding_bCharFormat cdc_stopbits);
+
+#ifdef	__cplusplus
+}
+#endif
+
+#endif	/* USB_CDCACM_H */
+