Added sketch of bit-bashing interface common code

src/include/gpxe/bitbash.h

@@ -0,0 +1,44 @@
+#ifndef _GPXE_BITBASH_H
+#define _GPXE_BITBASH_H
+
+/** @file
+ *
+ * Bit-bashing interfaces
+ *
+ */
+
+/** A bit-bashing interface */
+struct bit_basher {
+	/**
+	 * Set/clear output bit
+	 *
+	 * @v basher		Bit-bashing interface
+	 * @v bit_id		Bit number
+	 * @v data		Value to write
+	 * 
+	 * @c data will be 0 if a logic 0 should be written (i.e. the
+	 * bit should be cleared), or -1UL if a logic 1 should be
+	 * written (i.e. the bit should be set).  This is done so that
+	 * the method may simply binary-AND @c data with the
+	 * appropriate bit mask.
+	 */
+	void ( * write ) ( struct bit_basher *basher, unsigned int bit_id,
+			   unsigned long data );
+	/**
+	 * Read input bit
+	 *
+	 * @v basher		Bit-bashing interface
+	 * @v bit_id		Bit number
+	 * @ret zero		Input is a logic 0
+	 * @ret non-zero	Input is a logic 1
+	 */
+	int ( * read ) ( struct bit_basher *basher, unsigned int bit_id );
+	/** Delay between subsequent calls to write(), in microseconds */
+	unsigned int udelay;
+};
+
+extern void write_bit ( struct bit_basher *basher, unsigned int bit_id,
+			unsigned long data );
+extern int read_bit ( struct bit_basher *basher, unsigned int bit_id );
+
+#endif /* _GPXE_BITBASH_H */