Index: kernel/arch/riscv64/include/arch/drivers/ucb.h
===================================================================
--- kernel/arch/riscv64/include/arch/drivers/ucb.h	(revision fcfe4169dda3ad9ad8680247239c1e022a41acb6)
+++ kernel/arch/riscv64/include/arch/drivers/ucb.h	(revision fcfe4169dda3ad9ad8680247239c1e022a41acb6)
@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2017 Martin Decky
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ * - The name of the author may not be used to endorse or promote products
+ *   derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/** @addtogroup riscv64
+ * @{
+ */
+/** @file
+ */
+
+#ifndef KERN_riscv64_DRIVERS_UCB_H_
+#define KERN_riscv64_DRIVERS_UCB_H_
+
+#include <stddef.h>
+#include <stdint.h>
+#include <console/chardev.h>
+
+extern void htif_init(volatile uint64_t *, volatile uint64_t *);
+extern outdev_t *htifout_init(void);
+extern void htif_putchar(outdev_t *, const wchar_t);
+
+#endif
+
+/** @}
+ */
Index: kernel/arch/riscv64/src/drivers/ucb.c
===================================================================
--- kernel/arch/riscv64/src/drivers/ucb.c	(revision fcfe4169dda3ad9ad8680247239c1e022a41acb6)
+++ kernel/arch/riscv64/src/drivers/ucb.c	(revision fcfe4169dda3ad9ad8680247239c1e022a41acb6)
@@ -0,0 +1,93 @@
+/*
+ * Copyright (c) 2017 Martin Decky
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ * - The name of the author may not be used to endorse or promote products
+ *   derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <arch/drivers/ucb.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <console/chardev.h>
+#include <str.h>
+#include <mm/slab.h>
+
+#define HTIF_DEVICE_CONSOLE  1
+
+#define HTIF_CONSOLE_PUTC  1
+
+static volatile uint64_t *tohost;
+static volatile uint64_t *fromhost;
+
+static outdev_operations_t htifdev_ops = {
+	.write = htif_putchar,
+	.redraw = NULL,
+	.scroll_up = NULL,
+	.scroll_down = NULL
+};
+
+static void poll_fromhost()
+{
+	uint64_t val = *fromhost;
+	if (!val)
+		return;
+	
+	*fromhost = 0;
+}
+
+void htif_init(volatile uint64_t *tohost_addr, volatile uint64_t *fromhost_addr)
+{
+	tohost = tohost_addr;
+	fromhost = fromhost_addr;
+}
+
+outdev_t *htifout_init(void)
+{
+	outdev_t *htifdev = malloc(sizeof(outdev_t), FRAME_ATOMIC);
+	if (!htifdev)
+		return NULL;
+	
+	outdev_initialize("htifdev", htifdev, &htifdev_ops);
+	return htifdev;
+}
+
+static void htif_cmd(uint8_t device, uint8_t cmd, uint64_t payload)
+{
+	uint64_t val = (((uint64_t) device) << 56) |
+	    (((uint64_t) cmd) << 48) |
+	    (payload & UINT64_C(0xffffffffffff));
+	
+	while (*tohost)
+		poll_fromhost();
+	
+	*tohost = val;
+}
+
+void htif_putchar(outdev_t *dev, const wchar_t ch)
+{
+	if (ascii_check(ch))
+		htif_cmd(HTIF_DEVICE_CONSOLE, HTIF_CONSOLE_PUTC, ch);
+	else
+		htif_cmd(HTIF_DEVICE_CONSOLE, HTIF_CONSOLE_PUTC, U_SPECIAL);
+}