Add boilerplate for sifive,trace 'uart' driver

Signed-off-by: Nathaniel Graff <nathaniel.graff@sifive.com>

Makefile.am

@@ -75,6 +75,7 @@ nobase_include_HEADERS = \
 	metal/drivers/sifive_rtc0.h \
 	metal/drivers/sifive_spi0.h \
 	metal/drivers/sifive_test0.h \
+	metal/drivers/sifive_trace.h \
 	metal/drivers/sifive_uart0.h \
 	metal/drivers/sifive_wdog0.h \
 	metal/machine/inline.h \
@@ -178,6 +179,7 @@ libriscv__mmachine__@MACHINE_NAME@_a_SOURCES = \
 	src/drivers/sifive_rtc0.c \
 	src/drivers/sifive_spi0.c \
 	src/drivers/sifive_test0.c \
+	src/drivers/sifive_trace.c \
 	src/drivers/sifive_uart0.c \
 	src/drivers/sifive_wdog0.c \
 	src/button.c \

metal/drivers/sifive_trace.h

@@ -0,0 +1,23 @@
+/* Copyright 2019 SiFive, Inc */
+/* SPDX-License-Identifier: Apache-2.0 */
+
+#ifndef METAL__DRIVERS__SIFIVE_TRACE_H
+#define METAL__DRIVERS__SIFIVE_TRACE_H
+
+#include <metal/io.h>
+#include <metal/uart.h>
+#include <metal/compiler.h>
+
+struct __metal_driver_vtable_sifive_trace {
+    const struct metal_uart_vtable uart;
+};
+
+struct __metal_driver_sifive_trace;
+
+__METAL_DECLARE_VTABLE(__metal_driver_vtable_sifive_trace)
+
+struct __metal_driver_sifive_trace {
+    struct metal_uart uart;
+};
+
+#endif /* METAL__DRIVERS__SIFIVE_TRACE_H */

src/drivers/sifive_trace.c

@@ -0,0 +1,44 @@
+/* Copyright 2019 SiFive, Inc */
+/* SPDX-License-Identifier: Apache-2.0 */
+
+#include <metal/machine/platform.h>
+
+#ifdef METAL_SIFIVE_TRACE
+
+#include <metal/drivers/sifive_trace.h>
+#include <metal/machine.h>
+
+#define TRACE_REG(base, offset)   (((unsigned long)base + offset))
+#define TRACE_REGB(base, offset)  (__METAL_ACCESS_ONCE((__metal_io_u8  *)TRACE_REG(base, offset)))
+#define TRACE_REGW(base, offset)  (__METAL_ACCESS_ONCE((__metal_io_u32 *)TRACE_REG(base, offset)))
+
+int __metal_driver_sifive_trace_putc(struct metal_uart *trace, unsigned char c)
+{
+    long base = __metal_driver_sifive_trace_base(trace);
+    return 0;
+}
+
+int __metal_driver_sifive_trace_getc(struct metal_uart *trace, unsigned char *c)
+{
+    long base = __metal_driver_sifive_trace_base(trace);
+    return 0;
+}
+
+void __metal_driver_sifive_trace_init(struct metal_uart *trace, int baud_rate)
+{
+    long base = __metal_driver_sifive_trace_base(trace);
+}
+
+__METAL_DEFINE_VTABLE(__metal_driver_vtable_sifive_trace) = {
+    .uart.init          = __metal_driver_sifive_trace_init,
+    .uart.putc          = __metal_driver_sifive_trace_putc,
+    .uart.getc          = __metal_driver_sifive_trace_getc,
+
+    .uart.get_baud_rate = NULL,
+    .uart.set_baud_rate = NULL,
+
+    .uart.controller_interrupt = NULL,
+    .uart.get_interrupt_id     = NULL,
+};
+
+#endif /* METAL_SIFIVE_TRACE */