2 files changed, 53 insertions, 9 deletions
diff --git a/src/include/base3.h b/src/include/base3.h
new file mode 100644
index 0000000000..e92cc8bae7
--- /dev/null
+++ b/src/include/base3.h
@@ -0,0 +1,48 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright 2014 Google Inc.
+ *
+ * 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; version 2 of the License.
+ *
+ * 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, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef __SRC_INCLUDE_BASE3_H__
+#define __SRC_INCLUDE_BASE3_H__
+
+/* We translate a floating pin (Z) as the ternary digit 2. */
+#define Z 2
+
+/*
+ * This provides a variadic macro BASE3() that can be used to translate a set of
+ * pin states into its base-3 integer representation, even in the context of a
+ * static initializer. You can call it with any number of up to 6 arguments,
+ * e.g. BASE3(1, Z) -> 5 or BASE3(0, Z, 1, 0) -> 21. Just don't look too closely
+ * at how the sausage is made. (Pay extra attention to typos when expanding it!)
+ */
+#define _BASE3_IMPL_1(arg0, arg1, arg2, arg3, arg4, arg5) arg0
+#define _BASE3_IMPL_2(arg0, arg1, arg2, arg3, arg4, arg5) \
+	(arg1 + (3 * _BASE3_IMPL_1(arg0, arg1, arg2, arg3, arg4, arg5)))
+#define _BASE3_IMPL_3(arg0, arg1, arg2, arg3, arg4, arg5) \
+	(arg2 + (3 * _BASE3_IMPL_2(arg0, arg1, arg2, arg3, arg4, arg5)))
+#define _BASE3_IMPL_4(arg0, arg1, arg2, arg3, arg4, arg5) \
+	(arg3 + (3 * _BASE3_IMPL_3(arg0, arg1, arg2, arg3, arg4, arg5)))
+#define _BASE3_IMPL_5(arg0, arg1, arg2, arg3, arg4, arg5) \
+	(arg4 + (3 * _BASE3_IMPL_4(arg0, arg1, arg2, arg3, arg4, arg5)))
+#define _BASE3_IMPL_6(arg0, arg1, arg2, arg3, arg4, arg5) \
+	(arg5 + (3 * _BASE3_IMPL_5(arg0, arg1, arg2, arg3, arg4, arg5)))
+#define _BASE3_IMPL(arg0, arg1, arg2, arg3, arg4, arg5, NARGS, ...) \
+	_BASE3_IMPL##NARGS(arg0, arg1, arg2, arg3, arg4, arg5)
+#define BASE3(...) _BASE3_IMPL(__VA_ARGS__, _6, _5, _4, _3, _2, _1)
+
+#endif /* __SRC_INCLUDE_BASE3_H__ */
diff --git a/src/include/gpio.h b/src/include/gpio.h
index af06697050..b2a341dabc 100644
--- a/src/include/gpio.h
+++ b/src/include/gpio.h
@@ -36,17 +36,13 @@ void gpio_output(gpio_t gpio, int value);
 
 /*
  * Read the value presented by the set of GPIOs, when each pin is interpreted
- * as a number in 0..2 range depending on the external pullup situation.
+ * as a base-3 digit (LOW = 0, HIGH = 1, Z/floating = 2).
+ * Example: X1 = Z, X2 = 1 -> gpio_get_tristates({GPIO(X1), GPIO(X2)}) = 5
+ * BASE3() from <base3.h> can generate numbers to compare the result to.
  *
- * Depending on the third parameter, the return value is either a set of two
- * bit fields, each representing one GPIO value, or a number where each GPIO is
- * included multiplied by 3^gpio_num, resulting in a true tertiary value.
- *
- * gpio[]: pin positions to read. little-endian (less significant value first).
+ * gpio[]: pin positions to read. gpio[0] is less significant than gpio[1].
  * num_gpio: number of pins to read.
- * tertiary: 1: pins are interpreted as a quad coded tertiary.
- *           0: pins are interpreted as a set of two bit fields.
  */
-int gpio_get_tristates(gpio_t gpio[], int num_gpio, int tertiary);
+int gpio_get_tristates(gpio_t gpio[], int num_gpio);
 
 #endif /* __SRC_INCLUDE_GPIO_H__ */