--- a/dac.pio	Fri Feb 21 17:27:22 2025 +1030
+++ b/dac.pio	Mon Feb 24 12:12:09 2025 +1030
@@ -6,15 +6,12 @@
 .define TRIGGER_IRQ 0
 ; Need 1 side set pin, the clock
 .side_set 1
-; Force load at address 0 so DMA handler can force a jump
-; presumably we could calculate the address but this is easier.
-.origin 0
 
 ; Clock in a 0 byte
-;    mov pins, null side 0
-;    nop side 1
-; Wait for start trigger
-;    wait 1 irq TRIGGER_IRQ side 0
+    mov pins, null side 0
+    nop side 1
+; Wait for start trigger and clear IRQ
+    wait 1 irq TRIGGER_IRQ side 0
 ; Clock DAC and write data from the FIFO
 ; DAC clocks data in on the rising clock edge
 ; Autopull is enabled so no need to pull

--- a/modulator.c	Fri Feb 21 17:27:22 2025 +1030
+++ b/modulator.c	Mon Feb 24 12:12:09 2025 +1030
@@ -51,13 +51,20 @@
 #define PHINV		0x04
 #define PACTIVE		0x08
 
+// DMA channel to feed DAC PIO
 static int dma_chan;
+// Pulse shape data
 uint8_t pulse_data[65536];
+// Pulse control data
 uint8_t pulse_ctrl[65536];
+// PWM slice for PRF timer
 unsigned slice_num = 0;
-PIO pulse_pio;
+// DAC PIO
+PIO pulse_pio = pio0;
+// DAC SM
 uint pulse_sm;
-
+// Instruction offset for DAC PIO program
+uint pulse_pio_sm_offset;
 /*
  * Use a DMA channel to feed PIO0 SM0 with pulse data.
  * Each DMA transfer is a single pulse.
@@ -73,10 +80,6 @@
 dma_handler(void) {
     // Clear the interrupt request.
     dma_hw->ints0 = 1u << dma_chan;
-    // Give the channel a new wave table entry to read from, and re-trigger it
-    //dma_channel_set_read_addr(dma_chan, shaped_trap_dat_start, true);
-    // Reset pulse state machine back to waiting for trigger
-    //pio_sm_exec(pulse_pio, pulse_sm, pio_encode_jump(0);
 }
 
 
@@ -90,8 +93,15 @@
   state = !state;
 #endif
 
-  // Trigger another pulse read out
+  // Reset DAQ PIO SM so it is waiting for a trigger
+  pio_sm_exec(pulse_pio, pulse_sm, pio_encode_jmp(pulse_pio_sm_offset));
+
+  // Setup next pulse DMA address
   dma_channel_set_read_addr(dma_chan, pulse_data, true);
+
+  // Manually trigger DAQ SM (cleared by SM)
+  pio0->irq_force = 1 << 0;
+
   gpio_put(2, 1);
   gpio_put(2, 0);
 }
@@ -304,17 +314,16 @@
     unsigned long long diff = absolute_time_diff_us(then, now);
     printf("Pulse computation took %lld usec and created %lu samples - %.1f nsec/sample\n",
 	   diff, idx, (float)diff * 1000.0 / idx);
-    __breakpoint();
+    //__breakpoint();
 
     // Load the clocked_input program, and configure a free state machine
     // to run the program.
-    PIO pulse_pio = pio0;
-    uint offset = pio_add_program(pulse_pio, &dac_program);
+    pulse_pio_sm_offset = pio_add_program(pulse_pio, &dac_program);
     uint pulse_sm = pio_claim_unused_sm(pulse_pio, true);
     // Data is GPIO7 to GPIO14, clock is GPIO15
     // Clock divisor of 2 so it runs at 60MHz and
     // generates a 30MHz clock
-    dac_program_init(pulse_pio, pulse_sm, offset, 7, 2);
+    dac_program_init(pulse_pio, pulse_sm, pulse_pio_sm_offset, 7, 2);
 
     // Configure a channel to write 32 bits at a time to PIO0
     // SM0's TX FIFO, paced by the data request signal from that peripheral.