root/sys/platform/pc64/isa/ic/i8237.h 
/*
 * Intel 8237 DMA Controller
 *
 * $FreeBSD: src/sys/i386/isa/ic/i8237.h,v 1.7 1999/08/28 00:45:14 peter Exp $
 * $DragonFly: src/sys/platform/pc64/isa/ic/i8237.h,v 1.1 2008/08/29 17:07:21 dillon Exp $
 */

#define DMA37MD_SINGLE  0x40    /* single pass mode */
#define DMA37MD_CASCADE 0xc0    /* cascade mode */
#define DMA37MD_AUTO    0x50    /* autoinitialise single pass mode */
#define DMA37MD_WRITE   0x04    /* read the device, write memory operation */
#define DMA37MD_READ    0x08    /* write the device, read memory operation */