diff -urN comedi-0.7.27/include/comedi.h comedi-0.7.27-test/include/comedi.h
--- comedi-0.7.27/include/comedi.h	Fri Oct 29 15:44:59 1999
+++ comedi-0.7.27-test/include/comedi.h	Thu Nov  4 21:27:54 1999
@@ -98,6 +98,8 @@
 #define SDF_MODE2	0x0200		/* can do mode 2 */
 #define SDF_MODE3	0x0400		/* can do mode 3 */
 #define SDF_MODE4	0x0800		/* can do mode 4 */
+#define SDF_ASYNC	0x1000		/* subdevice is capable of asynchronous commands */
+#define SDF_PERMBUF	0x2000		/* subdevice has a permanently allocated buffer */
 
 #define SDF_READABLE	0x00010000	/* subdevice can be read (e.g. analog input) */
 #define SDF_WRITEABLE	0x00020000	/* subdevice can be written (e.g. analog output) */
@@ -145,6 +147,10 @@
 #define COMEDI_CANCEL _IO(CIO,7)
 #define COMEDI_RANGEINFO _IOR(CIO,8,comedi_rangeinfo)
 #define COMEDI_CMD _IOR(CIO,9,comedi_cmd)
+#define COMEDI_SUBDCONFIG _IOW(CIO,10,comedi_subdconfig)
+#define COMEDI_SETBUFSIZE _IO(CIO,11)
+#define COMEDI_SETMAXBUFSIZE _IO(CIO,12)
+#define COMEDI_SETPERMBUF _IO(CIO,13)
 
 
 
@@ -156,6 +162,7 @@
 typedef struct comedi_subdinfo_struct comedi_subdinfo;
 typedef struct comedi_devinfo_struct comedi_devinfo;
 typedef struct comedi_devconfig_struct comedi_devconfig;
+typedef struct comedi_subdconfig_struct comedi_subdconfig;
 typedef struct comedi_rangeinfo_struct comedi_rangeinfo;
 typedef struct comedi_krange_struct comedi_krange;
 
@@ -228,7 +235,9 @@
 	lsampl_t	maxdata;
 	unsigned int	flags;		/* channel flags */
 	unsigned int	range_type;	/* lookup in kernel */
-	unsigned int unused[10];
+	unsigned int	max_buffer_size; /* maximum allowed buffer size */
+	unsigned int	buffer_size;	/* currently configured buffer size */
+	unsigned int unused[8];
 };
 
 struct comedi_devinfo_struct{
@@ -242,6 +251,12 @@
 struct comedi_devconfig_struct{
 	char board_name[COMEDI_NAMELEN];
 	int options[COMEDI_NDEVCONFOPTS];
+};
+
+struct comedi_subdconfig_struct{
+	unsigned int subdev;
+	unsigned int cmd;
+	long arg;
 };
 
 
diff -urN comedi-0.7.27/module/comedi_module.h comedi-0.7.27-test/module/comedi_module.h
--- comedi-0.7.27/module/comedi_module.h	Fri Oct 29 15:44:59 1999
+++ comedi-0.7.27-test/module/comedi_module.h	Thu Nov  4 21:12:08 1999
@@ -97,17 +97,38 @@
 
 struct comedi_subdevice_struct{
 	int type;
-	int n_chan;
-	int subdev_flags;
-	int timer_type;
-	int len_chanlist;		/* length of channel/gain list, if available */
 
-	void		*prealloc_buf;		/* pre-allocated buffer */
-	unsigned int	prealloc_bufsz;		/* buffer size, in bytes */
+	/* internal parameters */
 
+	void *private;
 	void *lock;
 	void *busy;
+	void		*buffer;
+	unsigned int	buffer_ref_count;
+
+	comedi_trig	cur_trig;	/* current trig structure */
+	comedi_cmd	cmd;
+	
+	volatile unsigned int buf_int_ptr;	/* buffer marker for interrupt */
+	unsigned int buf_user_ptr;		/* buffer marker for read() and write() */
+	volatile unsigned int buf_int_count;	/* byte count for interrupt */
+	unsigned int buf_user_count;		/* byte count for read() and write() */
+	unsigned int cur_chan;		/* useless channel marker for interrupt */
+
+	unsigned int state;
+
+	/* user-configurable parameters */
+
+	unsigned int	max_buffer_size;
+	unsigned int	buffer_size;
 	
+	/* informational parameters */
+
+	int n_chan;
+	int subdev_flags;
+	int timer_type;
+	int len_chanlist;		/* length of channel/gain list, if available */
+
 	int io_bits;
 	
 	lsampl_t maxdata;		/* if maxdata==0, use list */
@@ -121,18 +142,7 @@
 	
 	unsigned int *chanlist;		/* driver-owned chanlist (not used) */
 	
-	comedi_trig	cur_trig;	/* current trig structure */
-	comedi_cmd	cmd;
-	
-	volatile unsigned int buf_int_ptr;	/* buffer marker for interrupt */
-	unsigned int buf_user_ptr;		/* buffer marker for read() and write() */
-	volatile unsigned int buf_int_count;	/* byte count for interrupt */
-	unsigned int buf_user_count;		/* byte count for read() and write() */
-	unsigned int cur_chan;		/* useless channel marker for interrupt */
-	
-#if 0
-	unsigned int *range_list;	/* is this necessary? */
-#endif
+	/* virtual functions */
 	
 	int (*trig[5])(comedi_device *,comedi_subdevice *,comedi_trig *);
 
@@ -140,11 +150,11 @@
 	int (*poll)(comedi_device *,comedi_subdevice *);
 	int (*cancel)(comedi_device *,comedi_subdevice *);
 
+	/* callback parameters */
+
 	unsigned int cb_mask;
 	int (*cb_func)(unsigned int flags,void *);
 	void *cb_arg;
-
-	unsigned int state;
 };
 
 struct comedi_device_struct{
diff -urN comedi-0.7.27/module/module.c comedi-0.7.27-test/module/module.c
--- comedi-0.7.27/module/module.c	Fri Oct 29 15:44:59 1999
+++ comedi-0.7.27-test/module/module.c	Thu Nov  4 21:47:51 1999
@@ -43,8 +43,11 @@
 
 comedi_device *comedi_devices;
 
+int comedi_allocate_buffer(comedi_device *dev,comedi_subdevice *s);
+void comedi_free_buffer(comedi_device *dev,comedi_subdevice *s);
 
 static int do_devconfig_ioctl(comedi_device *dev,comedi_devconfig *arg,kdev_t minor);
+static int do_subdconfig_ioctl(comedi_device *dev,comedi_subdconfig *arg);
 static int do_devinfo_ioctl(comedi_device *dev,comedi_devinfo *arg);
 static int do_subdinfo_ioctl(comedi_device *dev,comedi_subdinfo *arg,void *file);
 static int do_chaninfo_ioctl(comedi_device *dev,comedi_chaninfo *arg);
@@ -85,6 +88,8 @@
 		return do_cancel_ioctl(dev,arg,file);
 	case COMEDI_CMD:
 		return do_cmd_ioctl(dev,(void *)arg,file);
+	case COMEDI_SUBDCONFIG:
+		return do_subdconfig_ioctl(dev,(void *)arg);
 	default:
 		return -EIO;
 	}
@@ -144,6 +149,54 @@
 	return -EINVAL;
 }
 
+/*
+   subdevice ioctls
+
+   the decision to make devices/subdevices, although stupid at
+   the time, seems _very_ stupid now.  These are 'subdevice specific'
+   ioctls.
+
+   fortunately, this should all be hidden behind a nice library
+   interface.
+ */
+static int do_subdconfig_ioctl(comedi_device *dev,comedi_subdconfig *arg)
+{
+	comedi_subdconfig it;
+	comedi_subdevice *s;
+
+	if(copy_from_user(&it,arg,sizeof(comedi_subdconfig)))
+		return -EFAULT;
+
+	if(it.subdev>=dev->n_subdevices)
+		return -EINVAL;
+	s=dev->subdevices+it.subdev;
+	
+	switch(it.cmd){
+	case COMEDI_SETBUFSIZE:
+		if(((unsigned int)it.arg)>=s->max_buffer_size)
+			return -EPERM;
+
+		if(s->buffer_ref_count)
+			return -EBUSY;
+
+		s->buffer_size=it.arg;
+
+		return 0;
+	case COMEDI_SETMAXBUFSIZE:
+		if(!suser())
+			return -EPERM;
+
+		s->max_buffer_size=it.arg;
+
+		return 0;
+	case COMEDI_SETPERMBUF:
+		if(it.arg)s->flags|=SDF_PERMBUF;
+		else s->flags&=~SDF_PERMBUF;
+
+		return 0;
+	}
+	return -EINVAL;
+}
 
 /*
 	COMEDI_DEVINFO
@@ -226,6 +279,8 @@
 		us->maxdata		= s->maxdata;
 		us->range_type		= s->range_type;
 		us->flags		= s->flags;
+		us->max_buffer_size	= s->max_buffer_size;
+		us->buffer_size		= s->buffer_size;
 		
 		if(s->busy)
 			us->subd_flags |= SDF_BUSY;
@@ -331,7 +386,7 @@
 {
 	comedi_trig user_trig;
 	comedi_subdevice *s;
-	int ret=0,i,bufsz;
+	int ret=0,i;
 	int reading;
 	
 #if 0
@@ -405,28 +460,13 @@
 		goto cleanup;
 	}
 	
-	if(!s->prealloc_bufsz){
-		/* allocate temporary buffer */
-
-		if(s->subdev_flags&SDF_LSAMPL){
-			bufsz=s->cur_trig.n*s->cur_trig.n_chan*sizeof(lsampl_t);
-		}else{
-			bufsz=s->cur_trig.n*s->cur_trig.n_chan*sizeof(sampl_t);
-		}
-
-		if(!(s->cur_trig.data=kmalloc(bufsz,GFP_KERNEL))){
-			DPRINTK("failed to allocate buffer\n");
-			ret=-ENOMEM;
-			goto cleanup;
-		}
-	}else{
-		bufsz=s->prealloc_bufsz;
-		if(!s->prealloc_buf){
-			printk("comedi: bug: s->prealloc_buf=NULL\n");
-		}
-		s->cur_trig.data=s->prealloc_buf;
+	if((ret=comedi_allocate_buffer(dev,s))<0){
+		ret=-ENOMEM;
+		goto cleanup;
 	}
-	s->cur_trig.data_len=bufsz;
+	s->cur_trig.data=s->buffer;
+	s->cur_trig.data_len=s->buffer_size;
+
 
 #if 0
 /* debugging */
@@ -498,10 +538,12 @@
 	}else{
 		i=ret*sizeof(sampl_t);
 	}
+#if 0
 	if(i>bufsz){
 		printk("comedi: (bug) trig returned too many samples\n");
 		i=bufsz;
 	}
+#endif
 	if(reading){
 		if(copy_to_user(user_trig.data,s->cur_trig.data,i)){
 			ret=-EFAULT;
@@ -603,12 +645,12 @@
 		goto cleanup;
 	}
 	
-	if(!s->prealloc_bufsz){
-		ret=-ENOMEM;
-		DPRINTK("no buffer (?)\n");
+	if((ret=comedi_allocate_buffer(dev,s))<0){
+		DPRINTK("buffer problems\n");
 		goto cleanup;
 	}
-	s->cmd.data_len=s->prealloc_bufsz;
+	s->cmd.data=s->buffer;
+	s->cmd.data_len=s->buffer_size;
 
 	s->buf_int_ptr=0;
 	s->buf_int_count=0;
@@ -805,6 +847,7 @@
 	comedi_device *dev=comedi_devices+minor;
 	comedi_subdevice *s;
 	int size;
+	int ret;
 
 	if(vma->vm_offset >= dev->n_subdevices)
 		return -EIO;
@@ -820,7 +863,10 @@
 	if(size>(1<<16))
 		return -EINVAL;
 
-	if(remap_page_range(vma->vm_start, virt_to_phys(s->prealloc_buf),
+	if((ret=comedi_allocate_buffer(dev,s))<0)
+		return ret;
+
+	if(remap_page_range(vma->vm_start, virt_to_phys(s->buffer),
 		size,vma->vm_page_prot))
 		return -EAGAIN;
 	
@@ -880,15 +926,13 @@
 	if(!(s->subdev_flags&SDF_WRITEABLE))
 		return -EIO;
 
-	if(!s->busy){
-		buf_ptr=s->prealloc_buf;
-		buf_len=s->prealloc_bufsz;
+	if(!s->busy && s->buffer){
+		buf_ptr=s->buffer;
+		buf_len=s->buffer_size;
 	}else{
 		if(s->busy != file)
 			return -EACCES;
-
-		buf_ptr=s->cur_trig.data;
-		buf_len=s->cur_trig.data_len;
+		return -ENOMEM;
 	}
 
 	if(!buf_ptr)
@@ -971,7 +1015,7 @@
 	if(!s->busy)
 		return 0;
 
-	if(!s->cur_trig.data || !(s->subdev_flags&SDF_READABLE))
+	if(!s->buffer || !(s->subdev_flags&SDF_READABLE))
 		return -EIO;
 
 	if(s->busy != file)
@@ -984,14 +1028,14 @@
 		n=nbytes;
 
 		m=s->buf_int_count-s->buf_user_count;
-		if(m>s->cur_trig.data_len){
+		if(m>s->buffer_size){
 			s->buf_user_count=s->buf_int_count;
 			s->buf_user_ptr=s->buf_int_ptr;
 			retval=-EINVAL; /* OVERRUN */
 			break;
 		}
-		if(s->buf_user_ptr+m > s->cur_trig.data_len){
-			m=s->cur_trig.data_len - s->buf_user_ptr;
+		if(s->buf_user_ptr+m > s->buffer_size){
+			m=s->buffer_size - s->buf_user_ptr;
 #if 0
 printk("m is %d\n",m);
 #endif
@@ -1015,7 +1059,7 @@
 			schedule();
 			continue;
 		}
-		m=copy_to_user(buf,((void *)(s->cur_trig.data))+s->buf_user_ptr,n);
+		m=copy_to_user(buf,s->buffer+s->buf_user_ptr,n);
 		if(m) retval=-EFAULT;
 		n-=m;
 		
@@ -1024,7 +1068,7 @@
 		s->buf_user_ptr+=n;
 		s->buf_user_count+=n;
 
-		if(s->buf_user_ptr>=s->cur_trig.data_len ){
+		if(s->buf_user_ptr>=s->buffer_size ){
 			s->buf_user_ptr=0;
 #if 0
 			if(s->subdev_flags & SDF_RUNNING)
@@ -1059,12 +1103,10 @@
 		s->cur_trig.chanlist=NULL;
 	}
 
-	if(s->cur_trig.data){
-		if(s->cur_trig.data != s->prealloc_buf)
-			kfree(s->cur_trig.data);
-
-		s->cur_trig.data=NULL;
+	if(s->cur_trig.data == s->buffer){
+		comedi_free_buffer(dev,s);
 	}
+	s->cur_trig.data=NULL;
 
 	s->buf_user_ptr=0;
 	s->buf_int_ptr=0;
@@ -1249,8 +1291,15 @@
 
 	for(i=0;i<dev->n_subdevices;i++){
 		s=dev->subdevices+i;
-		if(s->prealloc_buf)
-			vfree(s->prealloc_buf);
+		if(s->buffer){
+			if(s->buffer_ref_count!=1){
+				printk("buffer ref count != 1 (%d)\n",
+					s->buffer_ref_count);
+				s->buffer_ref_count=1;
+			}
+			comedi_free_buffer(dev,s);
+		}
+		if(s->private)kfree(s->private);
 	}
 	if(dev->rem)dev->rem(dev);
 	if(dev->subdevices)kfree(dev->subdevices);
@@ -1360,23 +1409,14 @@
 		if(s->type==COMEDI_SUBD_UNUSED)
 			continue;
 
-		if(s->len_chanlist==0)
-			s->len_chanlist=1;
-
-		/* XXX */
-		if(s->trig[1] || s->trig[2] || s->trig[3] ||s->trig[4]){
-			s->prealloc_bufsz=1024*128;
-		}else{
-			s->prealloc_bufsz=0;
+		if(s->trig[1] || s->trig[2] || s->trig[3] || s->trig[4]
+			|| s->do_cmd){
+			s->max_buffer_size=65536;
+			s->buffer_size=65536;
 		}
 
-		if(s->prealloc_bufsz){
-			/* XXX */
-			s->prealloc_buf=vmalloc(s->prealloc_bufsz*sizeof(sampl_t));
-			if(!s->prealloc_buf){
-				printk("ENOMEM\n");
-			}
-		}
+		if(s->len_chanlist==0)
+			s->len_chanlist=1;
 
 		if(!s->range_type && !s->range_type_list)
 			s->range_type=RANGE_unknown;
@@ -1635,4 +1675,36 @@
 }
 
 #endif
+
+/*
+   This function is called when we've decided we need a buffer.
+   If there is one permanently allocated, that is returned,
+   otherwise a temporary buffer is allocated.
+ */
+int comedi_allocate_buffer(comedi_device *dev,comedi_subdevice *s)
+{
+	if(!s->buffer_ref_count){
+		//s->buffer=kmalloc(s->buffer_size,GFP_KERNEL);
+		s->buffer=vmalloc(s->buffer_size);
+		if(!s->buffer){
+			printk("comedi: gack! no mem\n");
+			return -ENOMEM;
+		}
+	}
+	s->buffer_ref_count++;
+
+	return 0;
+}
+
+void comedi_free_buffer(comedi_device *dev,comedi_subdevice *s)
+{
+	s->buffer_ref_count--;
+
+	if(!s->buffer_ref_count){
+		//kfree(s->buffer);
+		vfree(s->buffer);
+		s->buffer=NULL;
+	}
+}
+
 
diff -urN comedi-0.7.27/module/ni-E.c comedi-0.7.27-test/module/ni-E.c
--- comedi-0.7.27/module/ni-E.c	Fri Oct 29 15:44:59 1999
+++ comedi-0.7.27-test/module/ni-E.c	Thu Nov  4 19:47:03 1999
@@ -836,6 +836,37 @@
 	return 0;
 }
 
+/* ai command */
+
+static int ni_ai_cmd(comedi_device *dev,comedi_subdevice *s)
+{
+	comedi_cmd *cmd=&s->cmd;
+
+	if(   cmd->start_src==TRIG_NOW
+	   && cmd->scan_begin_src==TRIG_TIMER
+	   && cmd->convert_src==TRIG_TIMER
+	   && cmd->scan_end_src==TRIG_COUNT
+	   && cmd->stop_src==TRIG_COUNT){
+		comedi_trig *trig=&s->cur_trig;
+
+		trig->subdev=0;
+		trig->mode=2;
+		trig->flags=0;
+		trig->n_chan=cmd->scan_end_arg;
+		trig->data=cmd->data;
+		trig->chanlist=cmd->chanlist;
+		trig->n=cmd->stop_arg;
+		trig->trigsrc=0;
+		trig->trigvar=cmd->convert_arg/20-1;
+		trig->trigvar1=cmd->scan_begin_arg/20-1;
+		trig->data_len=cmd->data_len;
+
+		return ni_ai_mode2(dev,s,trig);
+	}
+
+	return -EIO;
+}
+
 
 static void ni_ao_fifo_load(comedi_device *dev,comedi_subdevice *s,
 		sampl_t *data,int n)
@@ -1214,6 +1245,7 @@
 	s->trig[1]=ni_ai_mode1;		/* not true mode 1 */
 	s->trig[2]=ni_ai_mode2;
 	s->trig[4]=ni_ai_mode4;
+	s->do_cmd=ni_ai_cmd;
 	s->cancel=ni_ai_reset;
 	
 	/* analog output subdevice */