diff --git a/common/sram-common.h b/common/sram-common.h
index 54cc45e..78e8c3a 100644
--- a/common/sram-common.h
+++ b/common/sram-common.h
@@ -13,11 +13,12 @@
  * read.  Requires these macros (with sample definitions):
  *
  * #define SRAM_MARCH_TEST_START(bank) sram_start_bank(bank)
- * #define SRAM_MARCH_TEST_DATA(data) sram_write(&data, 1)
+ * #define SRAM_MARCH_TEST_DATA(offset, data) sram_write(&data, 1)
  * #define SRAM_MARCH_TEST_END() sram_flush_and_release_bank()
  */
 bool sram_march_test(int pass) {
-  SRAM_MARCH_TEST_START(pass & 1);
+  int bank = pass & 1;
+  SRAM_MARCH_TEST_START(bank);
 
   switch (pass) {
     // Bit-sliding test.
@@ -46,32 +47,54 @@ bool sram_march_test(int pass) {
     case 13:
     case 14:
     case 15:
-      for (int i = 0; i < SRAM_BANK_SIZE_BYTES; ++i) {
-        int bit = (i + pass / 2) % 8;
+      for (int offset = 0; offset < SRAM_BANK_SIZE_BYTES; ++offset) {
+        int bit = (offset + pass / 2) % 8;
         uint8_t data = 1 << bit;
-        SRAM_MARCH_TEST_DATA(data);
+        SRAM_MARCH_TEST_DATA(offset, data);
       }
       break;
 
     // Write the lowest 8 bits of the address to each byte of SRAM.
     case 16:
     case 17:
-      for (int i = 0; i < SRAM_BANK_SIZE_BYTES; ++i) {
-        uint8_t data = i & 0xff;
-        SRAM_MARCH_TEST_DATA(data);
+      for (int offset = 0; offset < SRAM_BANK_SIZE_BYTES; ++offset) {
+        uint8_t data = offset & 0xff;
+        SRAM_MARCH_TEST_DATA(offset, data);
       }
       break;
 
     // Write the lowest 8 bits of the address (inverted) to each byte of SRAM.
     case 18:
     case 19:
-      for (int i = 0; i < SRAM_BANK_SIZE_BYTES; ++i) {
-        uint8_t data = (i & 0xff) ^ 0xff;
-        SRAM_MARCH_TEST_DATA(data);
+      for (int offset = 0; offset < SRAM_BANK_SIZE_BYTES; ++offset) {
+        uint8_t data = (offset & 0xff) ^ 0xff;
+        SRAM_MARCH_TEST_DATA(offset, data);
       }
       break;
+
+    // Write repeating sequences with prime periods, to avoid any periodic
+    // repeating on address bit boundaries (powers of 2).  To make bank 1
+    // different from bank 0, start counter at non-zero for bank 1.
+    case 20:
+    case 21: {
+      int primes[8] = { 251, 241, 239, 233, 229, 227, 223, 211 };
+      int prime_index = 0;
+      int offset = 0;
+      int counter = bank * 199;
+      for (; offset < SRAM_BANK_SIZE_BYTES; ++offset, ++counter) {
+        if (counter == primes[prime_index] * 255) {
+          prime_index = (prime_index + 1) % 8;
+          counter = 0;
+        }
+        uint8_t data = counter % primes[prime_index];
+        SRAM_MARCH_TEST_DATA(offset, data);
+      }
+      break;
+    }
   }
 
   SRAM_MARCH_TEST_END();
   return true;
 }
+
+#define SRAM_MARCH_TEST_NUM_PASSES 22
diff --git a/emulator-patches/blastem-0.6.2.patch b/emulator-patches/blastem-0.6.2.patch
index 7d2b130..ac5fec0 100644
--- a/emulator-patches/blastem-0.6.2.patch
+++ b/emulator-patches/blastem-0.6.2.patch
@@ -1,6 +1,6 @@
-commit 5126640d303a7411d7e84e8d41cfd5d92b88c1bd
-Author: Joey Parrish <joey.parrish@gmail.com>
-Date:   Wed Mar 27 07:39:28 2024 -0700
+commit 3c98e2a06d7c398d7b46b032c349837ebb43aa59
+Author: Joey Parrish <joeyparrish@google.com>
+Date:   Mon Sep 23 21:34:59 2024 -0700
 
     Emulate Kinetoscope hardware in BlastEm 0.6.2
     
@@ -21,7 +21,7 @@ index 0000000..8f39f7f
 +zdis
 +kinetoscope
 diff --git a/Makefile b/Makefile
-index 0dddc9f..f4c96df 100644
+index 0dddc9f..f8e4562 100644
 --- a/Makefile
 +++ b/Makefile
 @@ -109,6 +109,13 @@ endif
@@ -77,6 +77,15 @@ index 0dddc9f..f4c96df 100644
  
  %.tiles : %.spec
  	./img2tiles.py -s $< $@
+@@ -382,6 +398,8 @@ m68k.c : m68k.cpu cpu_dsl.py
+ res.o : blastem.rc
+ 	$(WINDRES) blastem.rc res.o
+ 
++kinetoscope/emulator-patches/kinetoscope.o: kinetoscope/emulator-patches/kinetoscope.c kinetoscope/emulator-patches/*.h kinetoscope/common/*.h
++
+ arrow.tiles : arrow.png
+ cursor.tiles : cursor.png
+ font_interlace_variable.tiles : font_interlace_variable.png
 diff --git a/build_release b/build_release
 index f5faa10..880044d 100755
 --- a/build_release
diff --git a/emulator-patches/kinetoscope.c b/emulator-patches/kinetoscope.c
index b1122b9..2471d90 100644
--- a/emulator-patches/kinetoscope.c
+++ b/emulator-patches/kinetoscope.c
@@ -74,8 +74,8 @@
 static void write_sram(uint32_t offset, const uint8_t* data, uint32_t size);
 
 // Macros to complete sram_march_test in sram-common.h
-#define SRAM_MARCH_TEST_START(bank) uint32_t offset = (pass & 1) * SRAM_BANK_SIZE_BYTES
-#define SRAM_MARCH_TEST_DATA(data) write_sram(offset++, &data, 1)
+#define SRAM_MARCH_TEST_START(bank) uint32_t bank_offset = bank ? SRAM_BANK_SIZE_BYTES : 0;
+#define SRAM_MARCH_TEST_DATA(offset, data) write_sram(offset + bank_offset, &data, 1)
 #define SRAM_MARCH_TEST_END() {}
 
 // Defines sram_march_test()
diff --git a/firmware/sram.cc b/firmware/sram.cc
index 6a77b05..c0a2498 100644
--- a/firmware/sram.cc
+++ b/firmware/sram.cc
@@ -15,7 +15,7 @@
 
 // Macros to complete sram_march_test in sram-common.h
 #define SRAM_MARCH_TEST_START(bank) sram_start_bank(bank)
-#define SRAM_MARCH_TEST_DATA(data) sram_write(&data, 1)
+#define SRAM_MARCH_TEST_DATA(offset, data) sram_write(&data, 1)
 #define SRAM_MARCH_TEST_END() sram_flush_and_release_bank()
 
 // Defines sram_march_test()
diff --git a/software/build.sh b/software/build.sh
index c17ef3a..acf728b 100755
--- a/software/build.sh
+++ b/software/build.sh
@@ -45,7 +45,7 @@ docker run \
   -v "$repo_root":/src \
   -u $(id -u):$(id -g) \
   -w "/src/$relative_dir" \
-  ghcr.io/stephane-d/sgdk:latest
+  ghcr.io/stephane-d/sgdk:working
 
 # SGDK's compiler makes the output executable, but that's not appropriate.
 chmod 644 $this_dir/out/rom.bin
diff --git a/software/hardware-test/src/main.c b/software/hardware-test/src/main.c
index 045dd5d..c75f3b2 100644
--- a/software/hardware-test/src/main.c
+++ b/software/hardware-test/src/main.c
@@ -36,8 +36,8 @@
 // Macros to complete sram_march_test in sram-common.h
 #define SRAM_MARCH_TEST_START(bank) \
   volatile uint8_t* sram = bank ? KINETOSCOPE_SRAM_BANK_1 : KINETOSCOPE_SRAM_BANK_0
-#define SRAM_MARCH_TEST_DATA(data) { \
-  if (sram[i] != data) { \
+#define SRAM_MARCH_TEST_DATA(offset, data) { \
+  if (sram[offset] != data) { \
     return false; \
   } \
 }
@@ -251,7 +251,7 @@ int main(bool hardReset) {
 
 
   // 13. Perform various intensive memory tests through the firmware.
-  // There are 20 different passes of this, with different patterns to verify.
+  // There are many different passes of this, with different patterns to verify.
   line++;  // blank line
   int memory_test_pass_line = line;
   line += 2;
@@ -260,9 +260,9 @@ int main(bool hardReset) {
   //            0         1
   //            012345678901234567
   VDP_drawText("SRAM test pass 00", 0, memory_test_pass_line);
-  VDP_drawText("....................", 1, memory_test_pass_line + 1);
+  VDP_drawText("......................", 1, memory_test_pass_line + 1);
 
-  for (int pass = 0; pass < 20; ++pass) {
+  for (int pass = 0; pass < SRAM_MARCH_TEST_NUM_PASSES; ++pass) {
     waitMs(1);
     *KINETOSCOPE_PORT_COMMAND = CMD_MARCH_TEST;
     *KINETOSCOPE_PORT_ARG = pass;