cores/usb/generic_device: option to force block ram allocations

lambdalib/cores/usb/generic_device.py

@@ -34,6 +34,7 @@ def __init__(self, pins,
             max_packet_size=None,
             with_cdc=True,
             with_microsoft_os_1_0=False,
+            force_contiguous_blockram=False,
             **kwargs):
 
         self.pins = pins
@@ -61,6 +62,7 @@ def __init__(self, pins,
         self.control_ep_handlers = []
         self.with_cdc = with_cdc
         self.with_microsoft_os_1_0 = with_microsoft_os_1_0
+        self.force_contiguous_blockram = force_contiguous_blockram
 
         self.kwargs = kwargs
 
@@ -116,6 +118,16 @@ def create_descriptors(self):
     def add_microsoft_os_1_0(self, descriptors):
         """ Add Microsoft OS 1.0 descriptors for Windows compatibility. """
 
+        if self.force_contiguous_blockram:
+            # This is a workaround for LUNA GetDescriptorHandlerBlock
+            # that only supports contiguous indexes for its ROM layout.
+            # We create fake descriptors as padding, to force BSRAM allocation
+            # for designs where building a non contiguous descriptor in
+            # LUTRAM is not an option (too many resources wasted)
+            # but we can spare some more BSRAM blocks.
+            while descriptors._next_string_index != 0xee:
+                descriptors.get_index_for_string(str(descriptors._next_string_index))
+
         descriptors.add_descriptor(get_string_descriptor("MSFT100\xee"), index=0xee)
 
         msft_descriptors = MicrosoftOS10DescriptorCollection()
@@ -161,7 +173,7 @@ def elaborate(self, platform):
             descriptors,
             # Windows compatible descriptors cannot be build in block ram
             # because MSFT string at index 0xee is not contiguous.
-            avoid_blockram=self.with_microsoft_os_1_0,
+            avoid_blockram=self.with_microsoft_os_1_0 and not self.force_contiguous_blockram,
         )
 
         # Add optional custom requests handlers (vendor)