Configure the 1680kB DMF format file system.

lib/vfs/fatfs.cc

@@ -80,6 +80,8 @@ public:
         currentFatFs = this;
         MKFS_PARM parm = {
             .fmt = FM_SFD | FM_ANY,
+			.n_root = _config.root_directory_entries(),
+			.au_size = _config.cluster_size(),
         };
         FRESULT res = f_mkfs("", &parm, buffer, sizeof(buffer));
         throwError(res);

lib/vfs/vfs.proto

@@ -17,7 +17,14 @@ message AcornDfsProto
 
 message Brother120FsProto {}
 
-message FatFsProto {}
+message FatFsProto {
+	optional uint32 cluster_size = 1
+		[ (help) = "cluster size (for new filesystems); 0 to select automatically",
+	      default = 0 ];
+	optional uint32 root_directory_entries = 2
+		[ (help) = "number of entries in the root directory (for new filesystems); 0 to select automatically",
+		  default = 0 ];
+}
 
 message CpmFsProto
 {

src/formats/ibm.textpb

@@ -291,6 +291,13 @@ option_group {
 					}
 				}
 			}
+
+			filesystem {
+				fatfs {
+					root_directory_entries: 16
+					cluster_size: 2048
+				}
+			}
 		}
 	}
 }