Add documentation on GPIO JSON

Document the JSON format for the GPIO configuration.

Change-Id: I74f9300f480724615ff031a7c75973224c86a760
Signed-off-by: Matt Spinler <spinler@us.ibm.com>

1 files changed, 69 insertions, 0 deletions

diff --git a/libopenbmc_intf/GPIOS.md b/libopenbmc_intf/GPIOS.md
new file mode 100644
index 0000000..3071648
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+++ b/libopenbmc_intf/GPIOS.md
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+# GPIO JSON format
+
+GPIO definitions are stored in '/etc/default/obmc/gpio/gpio_defs.json' on the
+BMC.  That file has 2 sections - 'gpio_configs' and 'gpio_definitions'.
+
+## gpio_configs
+
+This section contains the GPIOs used in power control.
+
+It looks like:
+```
+"gpio_configs": {
+    "power_config": {
+
+        #See code in op-pwrctl for details
+
+        #Required
+        "power_good_in": "...",
+
+        #Required
+        "power_up_outs": [
+            {"name": "...", "polarity": true/false},
+            {"name": "...", "polarity": true/false}
+        ],
+
+        #Optional
+        "reset_outs": [
+            {"name": "...", "polarity": true/false}
+        ],
+
+        #Optional
+        "latch_out": "...",
+
+        #Optional
+        "pci_reset_outs": [
+            {"name": "...", "polarity": true/false, "hold": true/false}
+        ]
+    }
+}
+```
+
+## gpio_definitions
+
+This section contains The GPIO pins and directions.
+
+It looks like:
+```
+    "gpio_definitions": [
+        {
+
+            #The name to look up this entry.
+            "name": "SOFTWARE_PGOOD",
+
+            #The GPIO pin.
+            "pin": "R1",
+
+            #Alternatively to the pin, can use 'num' which is the
+            #raw number the GPIO would be accessed with.
+            "num": 7,
+
+            #The GPIO direction - in, out, rising, falling, or both
+            "direction": "out"
+        },
+        {
+            ...
+        }
+    ]
+```
+