[coreboot-gerrit] New patch to review for coreboot: gpio: Add support for binary_first base3 number system
Julius Werner (jwerner@chromium.org)
gerrit at coreboot.org
Thu Mar 17 01:30:32 CET 2016
Julius Werner (jwerner at chromium.org) just uploaded a new patch set to gerrit, which you can find at https://review.coreboot.org/14116
-gerrit
commit 76fc774f902b268a71df30c881c9210fa9cca155
Author: Julius Werner <jwerner at chromium.org>
Date: Wed Mar 16 17:11:55 2016 -0700
gpio: Add support for binary_first base3 number system
This patch adds support for an alternative ternary number system which a
group of GPIOs can be interpreted in. In this system, the digit
combinations that would form a binary number (i.e. that contain no 'Z'
state) come first in their normal binary order, and all the combinations
that do contain a 'Z' come afterwards. We can use this for boards that
originally get strapped with binary board IDs but eventually require
more revisions than that representation allows. We can switch their code
to binary_first base3 and all old revisions with already produced boards
will still get read as the correct numbers.
Credit for the algorithm idea goes to Haran Talmon.
BRANCH=None
BUG=None
TEST=Stubbed out the actual GPIO reading and simulated all combinations
of 4 ternary digits for both number systems.
Change-Id: Ib5127656455f97f890ce2999ba5ac5f58a20cf93
Signed-off-by: Julius Werner <jwerner at chromium.org>
---
src/include/gpio.h | 35 ++++++++++++++++++++++++++++++++++-
src/lib/gpio.c | 49 +++++++++++++++++++++++++++++++++++++++++++++----
2 files changed, 79 insertions(+), 5 deletions(-)
diff --git a/src/include/gpio.h b/src/include/gpio.h
index ea03a23..443a580 100644
--- a/src/include/gpio.h
+++ b/src/include/gpio.h
@@ -29,6 +29,7 @@ void gpio_input_pulldown(gpio_t gpio);
void gpio_input_pullup(gpio_t gpio);
void gpio_input(gpio_t gpio);
void gpio_output(gpio_t gpio, int value);
+int _gpio_base3_value(gpio_t gpio[], int num_gpio, int binary_first);
/*
* Read the value presented by the set of GPIOs, when each pin is interpreted
@@ -48,6 +49,38 @@ int gpio_base2_value(gpio_t gpio[], int num_gpio);
* gpio[]: pin positions to read. gpio[0] is less significant than gpio[1].
* num_gpio: number of pins to read.
*/
-int gpio_base3_value(gpio_t gpio[], int num_gpio);
+static inline int gpio_base3_value(gpio_t gpio[], int num_gpio)
+{
+ return _gpio_base3_value(gpio, num_gpio, 0);
+}
+
+/*
+ * Read the value presented by the set of GPIOs, when each pin is interpreted
+ * as a base-3 digit (LOW = 0, HIGH = 1, Z/floating = 2) in a non-standard
+ * ternary number system where the first 2^n natural numbers are represented
+ * as they would be in a binary system (without any Z digits), and the following
+ * 3^n-2^n use the remaining ternary representations in their normal order.
+ * This is useful for boards which initially used a binary board ID and later
+ * decided to switch to tri-state after some revisions have already been built.
+ * Example: For num_gpio = 2 we get the following representation:
+ *
+ * Number X1 X0
+ * 0 0 0
+ * 1 0 1
+ * 2 1 0
+ * 3 1 1
+ * 4 0 2 // Skipping 00 and 01 which are already used up
+ * 5 1 2 // Skipping 10 and 11 which are already used up
+ * 6 2 0
+ * 7 2 1
+ * 8 2 2
+ *
+ * gpio[]: pin positions to read. gpio[0] is less significant than gpio[1].
+ * num_gpio: number of pins to read.
+ */
+static inline int gpio_binary_first_base3_value(gpio_t gpio[], int num_gpio)
+{
+ return _gpio_base3_value(gpio, num_gpio, 1);
+}
#endif /* __SRC_INCLUDE_GPIO_H__ */
diff --git a/src/lib/gpio.c b/src/lib/gpio.c
index 5147cfe..97733b8 100644
--- a/src/lib/gpio.c
+++ b/src/lib/gpio.c
@@ -35,7 +35,7 @@ int gpio_base2_value(gpio_t gpio[], int num_gpio)
return result;
}
-int gpio_base3_value(gpio_t gpio[], int num_gpio)
+int _gpio_base3_value(gpio_t gpio[], int num_gpio, int binary_first)
{
/*
* GPIOs which are tied to stronger external pull up or pull down
@@ -49,7 +49,11 @@ int gpio_base3_value(gpio_t gpio[], int num_gpio)
static const char tristate_char[] = {[0] = '0', [1] = '1', [Z] = 'Z'};
int temp;
int index;
- int result = 0;
+ int result;
+ int ternary = 0;
+ int binary = 0;
+ int has_z = 0;
+ int binary_below = 0;
char value[32];
assert(num_gpio <= 32);
@@ -84,9 +88,46 @@ int gpio_base3_value(gpio_t gpio[], int num_gpio)
temp = gpio_get(gpio[index]);
temp |= ((value[index] ^ temp) << 1);
printk(BIOS_DEBUG, "%c ", tristate_char[temp]);
- result = (result * 3) + temp;
+ ternary = (ternary * 3) + temp;
+
+ /*
+ * For binary_first we keep track of both the binary and the
+ * normal ternary result, and whether we found any pin that was
+ * a Z. We also determine the amount of numbers that can be
+ * represented with only binary digits (no Z) that come below
+ * the current value in normal ternary representation. Counting
+ * from the left, we add 2^i for any '1' digit to account for
+ * the binary numbers that would come below it if all following
+ * digits were '0'. As soon as we find a '2' digit we can total
+ * the remaining binary numbers below as 2^(i+1).
+ *
+ * Example: 1 0 2 1 (counting from the left / most significant)
+ * '1' at 3: Add 2^3 = 8 to account for binaries 0000-0111
+ * '0' at 2: Ignore (not all binaries 1000-1100 are below us)
+ * '2' at 1: Add 2^(1+1) = 4 to account for binaries 1000-1011
+ * Stop adding for lower digits, all already accounted now. We
+ * know that there can be no binary numbers in 1020-102X.
+ */
+ if (binary_first) {
+ binary = (binary * 2) + temp;
+ if (!has_z && temp == 1)
+ binary_below += 1 << index;
+ if (!has_z && temp == 2) {
+ binary_below += 1 << (index + 1);
+ has_z = 1;
+ }
+ }
}
- printk(BIOS_DEBUG, "= %d\n", result);
+
+ if (!binary_first)
+ result = ternary;
+ else if (has_z)
+ result = ternary + (1 << num_gpio) - binary_below;
+ else
+ result = binary;
+
+ printk(BIOS_DEBUG, "= %d (%s base3 number system)\n", result,
+ binary_first ? "binary_first" : "standard");
/* Disable pull up / pull down to conserve power */
for (index = 0; index < num_gpio; ++index)
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