Yet very simple Disk Caches module for use with SD cards

git-svn-id: https://svn.inf.ethz.ch/svn/lecturers/a2/trunk@8283 8c9fc860-2736-0410-a75d-ab315db34111

ARM/ARM.A2/DiskCaches.Mod

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+MODULE DiskCaches; (* Simple (disk) cache, fof 2018 *)
+IMPORT SYSTEM, Disks;
+
+	TYPE TransferProcedure = PROCEDURE {DELEGATE} (op,block,num: LONGINT; VAR data: ARRAY OF CHAR; ofs: LONGINT; VAR res: WORD);
+
+	CONST BlockSize = 512;
+	CONST NumberCacheLines = 128;
+
+	TYPE
+		CacheLine = RECORD
+			globalIndex: SIZE;
+			data: POINTER TO ARRAY OF CHAR;
+		END;
+
+	TYPE
+	
+	(* Yet very simple disk cache. 
+		- synchronous
+		- One-way associative
+		- Write-through
+	*)
+	Cache* = OBJECT
+	VAR
+		lines: ARRAY NumberCacheLines OF CacheLine;
+		blocksPerCacheLine: LONGINT;
+		transfer: TransferProcedure;
+
+		PROCEDURE &Init*(transfer: TransferProcedure; blocksPerCacheLine = 32: LONGINT);
+		VAR i: SIZE;
+		BEGIN
+			SELF.transfer := transfer;
+			SELF.blocksPerCacheLine := blocksPerCacheLine;
+			FOR i := 0 TO LEN(lines)-1 DO
+				lines[i].globalIndex := -1;
+				NEW(lines[i].data,blocksPerCacheLine * BlockSize );
+			END;
+		END Init;
+
+		(* LONGINTs for compatibility -- should be largely replaced by SIZEs ! *)
+		PROCEDURE Transfer* (op: LONGINT; block, num: LONGINT; VAR data: ARRAY OF CHAR; ofs: LONGINT; VAR res: LONGINT);
+		VAR globalIndex, lineIndex, lineOfs, lineFirstBlock, lineBlocks: LONGINT;
+		BEGIN
+			WHILE num > 0 DO
+				globalIndex := block DIV blocksPerCacheLine; (* global index *)
+				lineIndex := globalIndex MOD NumberCacheLines; (* (local) line index *)
+				lineOfs := block MOD blocksPerCacheLine; (* line offset in blocks *)
+				lineFirstBlock := block - lineOfs;
+				lineBlocks := MIN(num, blocksPerCacheLine - lineOfs); (* chunk size in bytes *)
+
+				IF (lines[lineIndex].globalIndex # globalIndex) THEN (* cacheline present *)
+					IF op = Disks.Read THEN (* read to cache *)
+						transfer(op, lineFirstBlock, blocksPerCacheLine, lines[lineIndex].data^, 0, res); (* assumes that lineFirstBlock is a valid block *)
+						lines[lineIndex].globalIndex := globalIndex;
+					END;
+				ELSIF op = Disks.Write THEN (* write to present cacheline *)
+					SYSTEM.MOVE(ADDRESS OF data[ofs], ADDRESS OF lines[lineIndex].data[lineOfs*BlockSize], lineBlocks*BlockSize);
+				END;
+
+				IF op = Disks.Write THEN (* always write through*)
+					transfer(op, block, lineBlocks, data, ofs, res);
+				ELSE (* read from cache *)
+					SYSTEM.MOVE(ADDRESS OF lines[lineIndex].data[lineOfs*BlockSize], ADDRESS OF data[ofs], lineBlocks*BlockSize);
+				END;
+				DEC(num, lineBlocks);
+				INC(block, lineBlocks);
+				INC(ofs, lineBlocks*BlockSize);
+			END;
+
+		END Transfer;
+
+	END Cache;
+
+END DiskCaches.
+
+(** USAGE PATTERN: 
+
+	VirtualDisk = OBJECT(Disks.Device)
+	VAR
+		...
+		cache: DiskCaches.Cache;
+
+		PROCEDURE TransferX*(op, block, num: LONGINT; VAR data: ARRAY OF CHAR; ofs: LONGINT; VAR res: WORD);
+		BEGIN
+			.... OLD TRANSFER CODE
+		END TransferX;
+		
+		PROCEDURE Transfer(op, block, num: LONGINT; VAR data: ARRAY OF CHAR; ofs: LONGINT; VAR res: WORD);
+		BEGIN{EXCLUSIVE}
+			cache.Transfer(op,block,num,data,ofs,res) 
+		END Transfer;
+
+		....		
+
+		PROCEDURE &Init(CONST name : ARRAY OF CHAR; blockSize, cyls, hds, spt : LONGINT);
+		BEGIN
+			NEW(cache, TransferX);
+			....
+		END Init;
+
+	END VirtualDisk;
+
+**)