diff --git a/tools/build_all_headers.py b/tools/build_all_headers.py
index fc047d999..a3e4f04b3 100755
--- a/tools/build_all_headers.py
+++ b/tools/build_all_headers.py
@@ -24,11 +24,15 @@
 IGNORE_DIRS.add('rp2_common/cmsis')
 IGNORE_DIRS.add('rp2_common/pico_async_context')
 IGNORE_DIRS.add('rp2_common/pico_btstack')
-IGNORE_DIRS.add('rp2_common/pico_cyw43_arch')
+#IGNORE_DIRS.add('rp2_common/pico_cyw43_arch')
 IGNORE_DIRS.add('rp2_common/pico_cyw43_driver')
 IGNORE_DIRS.add('rp2_common/pico_lwip')
 IGNORE_DIRS.add('rp2_common/pico_stdio_semihosting')
 IGNORE_DIRS.add('rp2_common/pico_stdio_usb')
+IGNORE_DIRS.add('rp2_common/pico_clib_interface')
+IGNORE_DIRS.add('rp2_common/pico_mbedtls')
+
+SORT_HEADERS_BY_DIRECTORY = True # if False, sort by filename
 
 if len(sys.argv) != 3:
     print("Usage: {} top_dir output_header".format(os.path.basename(sys.argv[0])))
@@ -54,7 +58,12 @@
         include_dirs.add(os.path.join(root, 'include'))
         dirs.remove('include')
 
-include_files = list()
+include_files_by_chip = {
+    'none': list(),
+    'rp2040': list(),
+    'rp2350': list(),
+}
+all_include_files = set()
 include_locations = dict()
 for d in sorted(include_dirs):
     for root, dirs, files in os.walk(d):
@@ -62,13 +71,69 @@
             if f.endswith('.h'):
                 include_file = os.path.relpath(os.path.join(root, f), d)
                 include_path = os.path.relpath(d, top_dir)
-                if include_file in include_files:
-                    raise Exception("Duplicate include file '{}' (found in both {} and {})".format(include_file, include_locations[include_file], include_path))
-                include_files.append(include_file)
+                if 'rp2040/' in include_path:
+                    include_files_by_chip['rp2040'].append(include_file)
+                elif 'rp2350/' in include_path:
+                    include_files_by_chip['rp2350'].append(include_file)
+                else:
+                    if include_file in include_files_by_chip['none']:
+                        raise Exception("Duplicate include file '{}' (found in both {} and {})".format(include_file, include_locations[include_file], include_path))
+                    include_files_by_chip['none'].append(include_file)
                 include_locations[include_file] = include_path
+                all_include_files.add(include_file)
+
+# figure out which includes are applicable to both chips
+include_files_by_chip['both'] = []
+for f in include_files_by_chip['rp2040']:
+    if f in include_files_by_chip['rp2350']:
+        include_files_by_chip['both'].append(f)
+        include_locations[f] = include_locations[f].replace('rp2350/', 'rp2xxx/')
+for f in include_files_by_chip['both']:
+    include_files_by_chip['rp2040'].remove(f)
+    include_files_by_chip['rp2350'].remove(f)
+
+if SORT_HEADERS_BY_DIRECTORY:
+    with open(output_header, 'w') as fh:
+        fh.write('''/*
+ * Copyright (c) 2021 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
 
-with open(output_header, 'w') as fh:
-    fh.write('''/*
+// This file is autogenerated, do not edit by hand
+
+''')
+        last_location = ''
+        for f in include_files_by_chip['none']:
+            if include_locations[f] != last_location:
+                fh.write('\n// {}\n'.format(include_locations[f]))
+            fh.write('#include "{}"\n'.format(f))
+            last_location = include_locations[f]
+        for f in include_files_by_chip['both']:
+            if include_locations[f] != last_location:
+                fh.write('\n// {}\n'.format(include_locations[f]))
+            fh.write('#include "{}"\n'.format(f))
+            last_location = include_locations[f]
+        if include_files_by_chip['rp2040']:
+            fh.write('\n#if PICO_RP2040\n')
+            for f in include_files_by_chip['rp2040']:
+                if include_locations[f] != last_location:
+                    fh.write('\n// {}\n'.format(include_locations[f]))
+                fh.write('#include "{}"\n'.format(f))
+                last_location = include_locations[f]
+            fh.write('\n#endif\n')
+        if include_files_by_chip['rp2350']:
+            fh.write('\n#if PICO_RP2350\n')
+            for f in include_files_by_chip['rp2350']:
+                if include_locations[f] != last_location:
+                    fh.write('\n// {}\n'.format(include_locations[f]))
+                fh.write('#include "{}"\n'.format(f))
+                last_location = include_locations[f]
+            fh.write('\n#endif\n')
+        fh.write('\n')
+else:
+    with open(output_header, 'w') as fh:
+        fh.write('''/*
  * Copyright (c) 2021 Raspberry Pi (Trading) Ltd.
  *
  * SPDX-License-Identifier: BSD-3-Clause
@@ -77,11 +142,22 @@
 // This file is autogenerated, do not edit by hand
 
 ''')
-    last_location = ''
-    for f in include_files:
-        if include_locations[f] != last_location:
-            fh.write('\n// {}\n'.format(include_locations[f]))
-        fh.write('#include "{}"\n'.format(f))
-        last_location = include_locations[f]
-    fh.write('\n')
+        last_define = None
+        for f in sorted(all_include_files, key=lambda x: os.path.split(x)):
+            if f in include_files_by_chip['rp2040']:
+                define = 'PICO_RP2040'
+            elif f in include_files_by_chip['rp2350']:
+                define = 'PICO_RP2350'
+            else:
+                define = None
+            if define != last_define:
+                if last_define is not None:
+                    fh.write('#endif\n')
+                if define is not None:
+                    fh.write('#if {}\n'.format(define))
+            fh.write('#include "{}"\n'.format(f))
+            last_define = define
+        if last_define is not None:
+            fh.write('#endif\n')
+        fh.write('\n')