1 files changed, 31 insertions, 10 deletions

diff --git a/device-functions.c b/device-functions.c
index 47a5bcd..ee62cf1 100644
--- a/device-functions.c
+++ b/device-functions.c
@@ -735,7 +735,7 @@ int Set_Delay(int check_possible_only,int word_override,int range_override,int c
 {
 	int word_out;  /* what is sent to the DAC */
 	int cap_range_control;	/* what is actually sent to shift register */
-	float setting;
+	float adj_setting, setting, min_one_shot_delay;
 	int point_found,relay_range,UseNegData,entry,actual_pol,dummy;
 
 	/* abandon if high channel selected by user but not enabled by firmware */
@@ -754,24 +754,45 @@ int Set_Delay(int check_possible_only,int word_override,int range_override,int c
 		}
 	}
 
-	setting=set_delay-globals.Flash.propagation_delay[channel];
+	/* won't work for all values if apparent fixed delay is less than minimum variable delay */
+	min_one_shot_delay = globals.Flash.delay_pwl_time[channel][0][0][0];
+	if (globals.Flash.delay_shrink[channel] < min_one_shot_delay) {
+		return HardwareError;
+	}
+
+	/* If we need the advance mode for all positive values of delay (for the external trigger
+ 	   mode to work as expected), then we must have 
+
+		( Flash.delay_shrink - Flash.propagation_delay ) >= min_one_shot_delay
+
+		shrink ~ fixed DDU delay (around 25 ns)
+		prop ~ propagation delay of main PG - prog delay of SYNC
 
+	   This is not normally the case, because Flash.propagation_delay can be large.
+
+	   If necessary, delay_shrink can be increased by using a larger DDU, or the
+	   propagation_delay difference can be reduced by increasing the delay of the
+	   SYNC pulse.
+	*/
+
+	
 	/* tweak depending on polarity */
+	adj_setting = set_delay;
 	if (globals.ChannelState[channel].amplitude<0.0) {
-		setting -= globals.Flash.delay_pol_tweak[channel][1];
+		adj_setting -= globals.Flash.delay_pol_tweak[channel][1];
 	} else {
-		setting -= globals.Flash.delay_pol_tweak[channel][0];
+		adj_setting -= globals.Flash.delay_pol_tweak[channel][0];
 	}
 
-	if (setting >= 0.0) {
-		Set_AdvDel(channel,to_Advance);
-	} else {
+	setting = adj_setting + globals.Flash.delay_shrink[channel] - globals.Flash.propagation_delay[channel];
+
+	if (setting >= min_one_shot_delay) {
+                Set_AdvDel(channel,to_Advance);
+        } else {
+		setting = globals.Flash.delay_shrink[channel] + globals.Flash.propagation_delay[channel] - adj_setting;
 		Set_AdvDel(channel,to_Delay);
-		setting *= -1;
 	}
 
-	setting=setting+globals.Flash.delay_shrink[channel];
-
 	/* protect against impossible settings during first turn-on */
 	if (setting<zero_equiv_timing) {
 		return HardwareError;