Tried using srand with rand to achieve more randomness. sudo cat /dev/pico_rng | rngtest -c 1000 still says that it is not even close to being good enough. Although, if we feed this data into the kernel with the other data sources it should be FIPS 140-2 compliant. By itself it is not.

firmware/pico_rng.c

@@ -5,6 +5,7 @@
  */
 
 #include <stdio.h>
+#include <stdlib.h>
 
 // Pico
 #include "pico/stdlib.h"
@@ -563,6 +564,23 @@ void get_random_data(char *buf, uint16_t len) {
         memcpy(&buf[i-1], (void*)&adc_result, 2);
     }
 
+    /**
+     * In an attempt to make the rng even more random this will slow down the amount of data the
+     * pico can generate. It appears to be more random, but not good enough for FIPS 140-2.
+     **/ 
+    /**
+    //Use the ADC as a seed to the arm gnu stdlib random number generator
+    srand((int)(adc_read() | (adc_read() << 16)));
+
+    memset(buf, 0, len);
+    int rand_result;
+    for(i = 0; i <= len-4; i=i+4)
+    {
+        rand_result = rand();
+        memcpy(&buf[i], (void*)&rand_result, 4);
+    }
+    **/
+
     gpio_put(25, 0);
 }