Turns out ekbb failed due to insufficient memory :-/

src/main/kotlin/Main.kt

@@ -12,7 +12,7 @@ import java.io.File
 fun main(args: Array<String>) {
 
     val tb = org.jline.terminal.TerminalBuilder.terminal()
-    var mbus = MemBus(32768)
+    var mbus = MemBus(65536)
     val tracer = Tracer()
     val loggingCollector = LoggingCollector()
     tracer.addCollector(loggingCollector)

src/main/kotlin/com/thequux/mcpdp/core/CPU.kt

@@ -898,6 +898,7 @@ class CPU(val mbus: MemBus, val tracer: ITracer = NullTracer()) {
                 is NonExistentMemoryError -> cpu_err or 0x20u
                 is BusTimeoutError -> cpu_err or 0x10u
             }
+            logger.warn("Threw error: ${error}")
             trap(0x04u)
         } catch (_: InvalidOpcodeException) {
             trap(0x10u)