diff --git a/sdk/boards/ibex-arty-a7-100.json b/sdk/boards/ibex-arty-a7-100.json
deleted file mode 100644
index db54172..0000000
--- a/sdk/boards/ibex-arty-a7-100.json
+++ /dev/null
@@ -1,76 +0,0 @@
-{
-    "devices": {
-        "clint": {
-            "start": 0x14001000,
-            "length": 0x1000
-        },
-        "plic": {
-            "start": 0x10000000,
-            "end": 0x10400000
-        },
-        "revoker": {
-            "start": 0x14000000,
-            "length": 0x1000
-        },
-        "uart": {
-            "start": 0x8f00b000,
-            "end":   0x8f00b100
-        },
-        "shadow" : {
-            "start": 0x200fe000,
-            "length": 0x2000
-        },
-        "gpio_led0" : {
-            "start": 0x8f00f000,
-            "length": 0x800
-        },
-        "kunyan_ethernet": {
-            "start": 0x14004000,
-            "end": 0x14008000
-        }
-    },
-    "instruction_memory": {
-        "start": 0x20040000,
-        "end": 0x20080000
-    },
-    "heap": {
-        "end": 0x20080000
-    },
-    "interrupts": [
-        {
-            "name": "RevokerInterrupt",
-            "number": 1,
-            "priority": 2
-        },
-        {
-            "name": "UARTInterrupt",
-            "number": 2,
-            "priority": 3,
-            "edge_triggered": true
-        },
-        {
-            "name": "EthernetTransmitInterrupt",
-            "number": 3,
-            "priority": 3
-        },
-        {
-            "name": "EthernetReceiveInterrupt",
-            "number": 4,
-            "priority": 3
-        }
-    ],
-    "defines" : [
-        "IBEX",
-        "IBEX_SAFE"
-    ],
-    "driver_includes" : [
-        "${sdk}/include/platform/arty-a7",
-        "${sdk}/include/platform/synopsis",
-        "${sdk}/include/platform/ibex",
-        "${sdk}/include/platform/generic-riscv"
-    ],
-    "timer_hz" : 33000000,
-    "tickrate_hz" : 100,
-    "revoker" : "hardware",
-    "stack_high_water_mark" : true
-}
diff --git a/sdk/boards/ibex-arty-a7-100.patch b/sdk/boards/ibex-arty-a7-100.patch
new file mode 100644
index 0000000..3170507
--- /dev/null
+++ b/sdk/boards/ibex-arty-a7-100.patch
@@ -0,0 +1,77 @@
+{
+  "base": "ibex-safe-simulator",
+  "patch": [
+    {
+      "op": "add",
+      "path": "/devices/gpio_led0",
+      "value": {
+        "start": 0x8f00f000,
+        "length": 0x800
+      }
+    },
+    {
+      "op": "add",
+      "path": "/kunyan_ethernet",
+      "value": {
+        "start": 0x14004000,
+        "end": 0x14008000
+      }
+    },
+    {
+      "op": "add",
+      "path": "/interrupts/1",
+      "value": {
+        "name": "UARTInterrupt",
+        "number": 2,
+        "priority": 3,
+        "edge_triggered": true
+      }
+    },
+    {
+      "op": "add",
+      "path": "/interrupts/2",
+      "value": {
+        "name": "EthernetTransmitInterrupt",
+        "number": 3,
+        "priority": 3
+      }
+    },
+    {
+      "op": "add",
+      "path": "/interrupts/3",
+      "value": {
+        "name": "EthernetReceiveInterrupt",
+        "number": 4,
+        "priority": 3
+      }
+    },
+    {
+      "op": "add",
+      "path": "/driver_includes/0",
+      "value": "${sdk}/include/platform/synopsis"
+    },
+    {
+      "op": "add",
+      "path": "/driver_includes/0",
+      "value": "${sdk}/include/platform/arty-a7"
+    },
+    {
+      "op": "replace",
+      "path": "/timer_hz",
+      "value": 33000000
+    },
+    {
+      "op": "replace",
+      "path": "/tickrate_hz",
+      "value": 100
+    },
+    {
+      "op": "remove",
+      "path": "/simulation"
+    },
+    {
+      "op": "remove",
+      "path": "/simulator"
+    }
+  ]
+}
diff --git a/sdk/boards/sonata-simulator.json b/sdk/boards/sonata-simulator.json
deleted file mode 100644
index 2573a40..0000000
--- a/sdk/boards/sonata-simulator.json
+++ /dev/null
@@ -1,144 +0,0 @@
-{
-    "devices": {
-        "shadow" : {
-            "start" : 0x30000000,
-            "end"   : 0x30000800
-        },
-        "pwm": {
-            "start" : 0x80001000,
-            "length": 0x00001000
-        },
-        "rgbled" : {
-            "start" : 0x80009000,
-            "end"   : 0x80009020
-        },
-        "revoker": {
-            "start" : 0x8000A000,
-            "length": 0x00001000
-        },
-        "adc": {
-            "start" : 0x8000B000,
-            "length": 0x00001000
-        },
-        "clint": {
-            "start" : 0x80040000,
-            "end"   : 0x80050000
-        },
-        "uart": {
-            "start" : 0x80100000,
-            "end"   : 0x80100034
-        },
-        "uart1": {
-            "start" : 0x80101000,
-            "end"   : 0x80101034
-        },
-        "uart2": {
-            "start" : 0x80102000,
-            "end"   : 0x80102034
-        },
-        "usbdev": {
-            "start" : 0x80400000,
-            "end"   : 0x80401000
-        },
-        "plic": {
-            "start" : 0x88000000,
-            "end"   : 0x88400000
-        }
-    },
-    "instruction_memory": {
-        "start": 0x00101000,
-        "end":   0x00120000
-    },
-    "heap": {
-        "end": 0x00120000
-    },
-    "revokable_memory_start": 0x00100000,
-    "defines" : [
-        "IBEX",
-        "SUNBURST",
-        "SUNBURST_SHADOW_BASE=0x30000000",
-        "SUNBURST_SHADOW_SIZE=0x800",
-        "ipconfigDRIVER_INCLUDED_RX_IP_CHECKSUM=1",
-        "ipconfigDRIVER_INCLUDED_TX_IP_CHECKSUM=1"
-    ],
-    "cxflags": "-mllvm -enable-machine-outliner=never",
-    "driver_includes" : [
-        "../include/platform/sunburst",
-        "../include/platform/ibex",
-        "../include/platform/generic-riscv"
-    ],
-    "timer_hz" : 40000000,
-    "tickrate_hz" : 100,
-    "revoker" : "hardware",
-    "stack_high_water_mark" : true,
-    "simulator" : "${sdk}/../scripts/run-sonata-sim.sh",
-    "simulation": true,
-    "interrupts": [
-        {
-            "name": "RevokerInterrupt",
-            "number": 1,
-            "priority": 2,
-            "edge_triggered": true
-        },
-        {
-            "name": "EthernetInterrupt",
-            "number": 2,
-            "priority": 3
-        },
-        {
-            "name": "UsbDevInterrupt",
-            "number": 3,
-            "priority": 3
-        },
-        {
-            "name": "Uart0Interrupt",
-            "number": 8,
-            "priority": 3
-        },
-        {
-            "name": "Uart1Interrupt",
-            "number": 9,
-            "priority": 3
-        },
-        {
-            "name": "Uart2Interrupt",
-            "number": 10,
-            "priority": 3
-        },
-        {
-            "name": "I2c0Interrupt",
-            "number": 16,
-            "priority": 3
-        },
-        {
-            "name": "I2c1Interrupt",
-            "number": 17,
-            "priority": 3
-        },
-        {
-            "name": "SpiLcdInterrupt",
-            "number": 24,
-            "priority": 3
-        },
-        {
-            "name": "SpiEthmacInterrupt",
-            "number": 25,
-            "priority": 3
-        },
-        {
-            "name": "Spi0Interrupt",
-            "number": 26,
-            "priority": 3
-        },
-        {
-            "name": "Spi1Interrupt",
-            "number": 27,
-            "priority": 3
-        },
-        {
-            "name": "Spi2Interrupt",
-            "number": 28,
-            "priority": 3
-        }
-    ]
-}
diff --git a/sdk/boards/sonata-simulator.patch b/sdk/boards/sonata-simulator.patch
new file mode 100644
index 0000000..650e419
--- /dev/null
+++ b/sdk/boards/sonata-simulator.patch
@@ -0,0 +1,15 @@
+{
+  "base": "sonata-prerelease",
+  "patch": [
+    {
+      "op": "replace",
+      "path": "/simulation",
+      "value": true
+    },
+    {
+      "op": "replace",
+      "path": "/simulator",
+      "value": "${sdk}/../scripts/run-sonata-sim.sh"
+    }
+  ]
+}
diff --git a/sdk/xmake.lua b/sdk/xmake.lua
index 0d02151..2ea30e5 100644
--- a/sdk/xmake.lua
+++ b/sdk/xmake.lua
@@ -253,21 +253,143 @@
 		target:set("cheriot.ldscript", "software_revoker.ldscript")
 	end)
 
--- Helper to get the board file for a given target
-local board_file = function(target)
-	local boardfile = target:values("board")
-	if not boardfile then
-		raise("target " .. target:name() .. " does not define a board name")
-	end
+-- Helper to find a board file given either the name of a board file or a path.
+local function board_file_for_name(boardName)
+	local boardfile = boardName
 	-- The directory containing the board file.
 	local boarddir = path.directory(boardfile);
+	-- If this isn't a path, look in the boards directory
 	if path.basename(boardfile) == boardfile then
 		boarddir = path.join(scriptdir, "boards")
-		boardfile = path.join(boarddir, boardfile .. '.json')
+		local fullBoardPath = path.join(boarddir, boardfile .. '.json')
+		if not os.isfile(fullBoardPath) then
+			fullBoardPath = path.join(boarddir, boardfile .. '.patch')
+		end
+		if not os.isfile(fullBoardPath) then
+			print("unable to find board file " .. boardfile .. ".  Try specifying a full path")
+			return nil
+		end
+		boardfile = fullBoardPath
 	end
 	return boarddir, boardfile
 end
 
+-- Helper to get the board file for a given target
+local function board_file_for_target(target)
+	local boardName = target:values("board")
+	if not boardName then
+		print("target " .. target:name() .. " does not define a board name")
+		return nil
+	end
+	return board_file_for_name(boardName)
+end
+
+-- Helper to load a board file.  This must be passed the json object provided
+-- by import("core.base.json") because import does not work in helper
+-- functions at the top level.
+local function load_board_file(json, boardFile)
+	if path.extension(boardFile) == ".json" then
+		return json.loadfile(boardFile)
+	end
+	if path.extension(boardFile) ~= ".patch" then
+		print("unknown extension for board file: " .. boardFile)
+		return nil
+	end
+	local patch = json.loadfile(boardFile)
+	if not patch.base then
+		print("Board file " .. boardFile .. " does not specify a base")
+		return nil
+	end
+	local _, baseFile = board_file_for_name(patch.base)
+	local base = load_board_file(json, baseFile)
+
+	-- If a string value is a number, return it as number, otherwise return it
+	-- in its original form.
+	function asNumberIfNumber(value)
+		if tostring(tonumber(value)) == value then
+			return tonumber(value)
+		end
+		return value
+	end
+
+	-- Heuristic to tell a Lua table is probably an array in Lua
+	-- This is O(n), but n is usually very small, and this happens once per
+	-- build so this doesn't really matter.
+	function isarray(t)
+		local i = 1
+		for k, v in pairs(t) do
+			if k ~= i then
+				return false
+			end
+			i = i+1
+		end
+		return true
+	end
+
+	for _, p in ipairs(patch.patch) do
+		if not p.op then
+			print("missing op in "..json.encode(p))
+			return nil
+		end
+		if not p.path or (type(p.path) ~= "string") then
+			print("missing or invalid path in "..json.encode(p))
+			return nil
+		end
+
+		-- Parse the JSON Pointer into an array of filed names, converting
+		-- numbers into Lua numbers if we see them.  This is not quite right,
+		-- because it doesn't handle field names with / in them, but we don't
+		-- currently use those for anything.  It also assumes that we really do
+		-- mean array indexes when we say numbers.  If we have an object with
+		-- "3" as the key and try to replace 3, it will currently not do the
+		-- right thing.  
+		local objectPath = {}
+		for entry in string.gmatch(p.path, "/([^/]+)") do
+			table.insert(objectPath, asNumberIfNumber(entry))
+		end
+
+		if #objectPath < 1 then
+			print("invalid path in "..json.encode(p))
+			return nil
+		end
+
+		-- Last path object is the name of the key we're going to modify.
+		local nodeName = table.remove(objectPath)
+		-- Walk the path to find the object that we're going to modify.
+		local nodeToModify = base
+		for _, pathComponent in ipairs(objectPath) do
+			nodeToModify = nodeToModify[pathComponent]
+		end
+
+		-- JSON arrays are indexed from 0, Lua's are from 1.  If someone says
+		-- array index 0, we need to map that to 1, and so on.
+		local isArrayOperation = false
+		if (type(nodeName) == "number") and isarray(nodeToModify) then
+			nodeName = nodeName + 1
+			isArrayOperation = true
+		end
+
+		-- Handle the operation
+		if (p.op == "replace") or (p.op == "add") then
+			if not p.value then
+				print(tostring(p.op).. " requires a value, missing in ", json.encode(p))
+				return nil
+			end
+			if isArrayOperation and p.op == "add" then
+				table.insert(nodeToModify, nodeName, p.value)
+			else
+				nodeToModify[nodeName] = p.value
+			end
+		elseif p.op == "remove" then
+			nodeToModify[nodeName] = nil
+		else
+			print(tostring(p.op) .. " is not a valid operation in ", json.encode(p))
+			return nil
+		end
+	end
+	return base
+end
+
 -- Helper to visit all dependencies of a specified target exactly once and call
 -- a callback.
 local function visit_all_dependencies_of(target, callback)
@@ -284,14 +406,13 @@
 	visit(target)
 end
 
-
 -- Rule for defining a firmware image.
 rule("firmware")
 	on_run(function (target)
 		import("core.base.json")
 		import("core.project.config")
-		local boarddir, boardfile = board_file(target)
-		local board = json.loadfile(boardfile)
+		local boarddir, boardfile = board_file_for_target(target)
+		local board = load_board_file(json, boardfile)
 		if not board.simulator then
 			raise("board description " .. boardfile .. " does not define a run command")
 		end
@@ -339,9 +460,10 @@
 			visit_all_dependencies_of(target, callback)
 		end
 
-		local boarddir, boardfile = board_file(target);
-		local board = json.loadfile(boardfile)
-
+		local boarddir, boardfile = board_file_for_target(target);
+		local board = load_board_file(json, boardfile)
+		print("Board file saved as ", target:targetfile()..".board.json")
+		json.savefile(target:targetfile()..".board.json", board)
 
 		-- Add defines to all dependencies.
 		local add_defines = function (defines)