diff --git a/src/fixkey-main.c b/src/fixkey-main.c
index f76a6bb..e70f10f 100644
--- a/src/fixkey-main.c
+++ b/src/fixkey-main.c
@@ -2,19 +2,61 @@
 // Created by nock on 2019-05-21.
 //
 
-#include <unistd.h>
+#include <errno.h>
 #include <getopt.h>
 #include <memory.h>
 #include <stdint.h>
 #include <stdio.h>
-#include <errno.h>
+#include <stdlib.h>
+#include <unistd.h>
 
 #include "fixkey-msg.h"
 #include "serial_util.h"
 #include "timer.h"
 
 #define DEFAULT_SERIAL_PORT "/dev/ttyUSB0"
-#define RESPONSE_LEN 2
+#define MAX_RESPONSE_LEN 11
+
+static void read_response(int serial_fd, uint8_t *dest, size_t *len) {
+    static uint8_t buf[MAX_RESPONSE_LEN] = {0};
+    static uint8_t *p = buf;
+    timer_start(3);
+    while (true) {
+        int bytes_read = read(serial_fd, p, MAX_RESPONSE_LEN);
+        if (bytes_read < 0) {
+            if (errno == EAGAIN) {
+                if (timer_expired()) {
+                    fprintf(stderr, "Timeout waiting for bootloader\n");
+                    exit(3);
+                }
+                usleep(250000);
+                continue;
+            }
+            fprintf(stderr, "Failed to read from serial port: %s\n", strerror(errno));
+            exit(1);
+        }
+        p += bytes_read;
+        uint8_t *nl_p = memchr(buf, '\r', p-buf);
+        if (nl_p) {
+            *len = nl_p - buf;
+            memcpy(dest, buf, *len);
+            uint16_t new_buf_len = p - nl_p - 1; // +1 skips trailing \n
+            if (new_buf_len) {
+                p = buf;
+                return;
+            }
+            memcpy(buf, nl_p+2, new_buf_len);
+            p = buf+new_buf_len;
+            break;
+        }
+    }
+}
+
+void dump_unexpected_response(uint8_t *buf, size_t len){
+    uint8_t tmp[MAX_RESPONSE_LEN+1] = {0};
+    memcpy(tmp, buf, len);
+    fprintf(stderr, "Rx'd unexpected response: %s\n", tmp);
+}
 
 int main(int argc, char **argv) {
     int c;
@@ -32,27 +74,27 @@ int main(int argc, char **argv) {
 
     write(serial_fd, fixkey_msg, sizeof(fixkey_msg));
 
-    int bytes_read;
-    uint8_t buf[RESPONSE_LEN];
+    size_t out_len;
+    uint8_t buf[MAX_RESPONSE_LEN];
 
-    timer_start(3);
-    while ((bytes_read = read(serial_fd, buf, RESPONSE_LEN)) < RESPONSE_LEN) {
-        if (bytes_read < 0 && errno != EAGAIN) {
-            fprintf(stderr, "Failed to read response\n");
-            return 2;
-        }
-        if (timer_expired()) {
-            fprintf(stderr, "Timeout waiting for response from bootloader\n");
-            return 3;
-        }
-        usleep(250000);
-    }
-    if (!memcmp(buf, "ok", RESPONSE_LEN)) {
-        return 0;
+    read_response(serial_fd, buf, &out_len);
+    if (!memcmp(buf, "hi", 2)) {
+        printf("Received confirmation that payload is running");
     } else {
-        uint8_t tmp[RESPONSE_LEN+1] = {0};
-        memcpy(tmp, buf, RESPONSE_LEN);
-        fprintf(stderr, "Rx'd unexpected response: %s\n", tmp);
+        dump_unexpected_response(buf, out_len);
     }
-    return 1;
+
+    read_response(serial_fd, buf, &out_len);
+    if (!memcmp(buf, "ok", 2)) {
+        printf("Payload reports success");
+        return 0;
+    } else if (!memcmp(buf, "badisn", 6)) {
+        fprintf(stderr, "Payload reports unexpected flash contents");
+        return 2;
+    } else if (!memcmp(buf, "patchfail", 9)) {
+        fprintf(stderr, "Payload reports that patch failed to apply");
+        return 3;
+    }
+    dump_unexpected_response(buf, out_len);
+    return 4;
 }
\ No newline at end of file
diff --git a/src/image.c b/src/image.c
index eb7dba2..7092fb9 100644
--- a/src/image.c
+++ b/src/image.c
@@ -25,6 +25,11 @@
 #define IMAGE_CHUNK_SIZE 124 //216 // 124 for identical output to newtmgr
 #define MACRO_CHUNK_SIZE 302 //432 // 302 ""
 
+/*
+ * Larger values above greatly increase speed, but seem to break older
+ * versions of mcuboot (like the one shipped with inital EM firmware)
+ */
+
 #define CRC16_INITIAL_CRC       0       /* what to seed crc16 with */
 #define CRC_CITT_POLYMINAL 0x1021