diff --git a/libgm/include/Die.hpp b/libgm/include/Die.hpp
index c751638..5c0705b 100644
--- a/libgm/include/Die.hpp
+++ b/libgm/include/Die.hpp
@@ -38,7 +38,11 @@ class Die
     static constexpr int LATCH_BLOCK_SIZE = 112;
     static constexpr int RAM_BLOCK_SIZE = 27;
     static constexpr int MEMORY_SIZE = 5120;
-    static constexpr int PLL_CONFIG_SIZE = 12 * 8 + 4 + 8;
+    static constexpr int MAX_PLL = 4;
+    static constexpr int PLL_CFG_SIZE = 12;
+    static constexpr int CLKIN_CFG_SIZE = 4;
+    static constexpr int GLBOUT_CFG_SIZE = 8;
+    static constexpr int PLL_CONFIG_SIZE = PLL_CFG_SIZE * MAX_PLL * 2 + CLKIN_CFG_SIZE + GLBOUT_CFG_SIZE;
 
   public:
     explicit Die();
@@ -53,6 +57,8 @@ class Die
     bool is_ram_empty(int x, int y) const;
     bool is_ram_data_empty(int x, int y) const;
     bool is_pll_cfg_empty(int index) const;
+    bool is_clkin_cfg_empty() const;
+    bool is_glbout_cfg_empty() const;
 
     void write_latch(int x, int y, const std::vector<uint8_t> &data);
     void write_ram(int x, int y, const std::vector<uint8_t> &data);
diff --git a/libgm/src/Bitstream.cpp b/libgm/src/Bitstream.cpp
index 0fb660b..2007538 100644
--- a/libgm/src/Bitstream.cpp
+++ b/libgm/src/Bitstream.cpp
@@ -324,12 +324,13 @@ class BitstreamReadWriter
         write_nops(6);
     }
 
-    void write_cmd_pll(int index, std::vector<uint8_t> data)
+    void write_cmd_pll(int index, std::vector<uint8_t> data, int size)
     {
-        write_header(CMD_PLL, 24);
-        for (int i = 0; i < 12; i++)
-            write_byte(data[i + index * 12]);
-        for (int i = 12 * 8; i < 12 * 8 + 12; i++)
+        write_header(CMD_PLL, size);
+        for (int i = 0; i < Die::PLL_CFG_SIZE; i++)
+            write_byte(data[i + index * Die::PLL_CFG_SIZE]);
+        int pos = Die::PLL_CFG_SIZE * Die::MAX_PLL * 2;
+        for (int i = pos; i < pos + size - Die::PLL_CFG_SIZE; i++)
             write_byte(data[i]);
         insert_crc16();
         write_nops(6);
@@ -592,15 +593,20 @@ Bitstream Bitstream::serialise_chip(const Chip &chip)
     auto &die = chip.get_die(0);
     std::vector<uint8_t> pll_data = die.get_pll_config();
     bool pll_written = false;
-    for (int i = 0; i < 4; i++) {
+    for (int i = 0; i < Die::MAX_PLL; i++) {
         bool cfg_a = !die.is_pll_cfg_empty(i * 2 + 0);
         bool cfg_b = !die.is_pll_cfg_empty(i * 2 + 1);
+        int size = Die::PLL_CFG_SIZE;
+        if (!die.is_clkin_cfg_empty())
+            size = Die::PLL_CFG_SIZE + Die::CLKIN_CFG_SIZE;
+        if (!die.is_glbout_cfg_empty())
+            size = Die::PLL_CFG_SIZE + Die::CLKIN_CFG_SIZE + Die::GLBOUT_CFG_SIZE;
         if (cfg_a || cfg_b) {
             wr.write_cmd_spll(1 << i);
-            wr.write_cmd_pll(i * 2, pll_data);
+            wr.write_cmd_pll(i * 2, pll_data, size);
             if (cfg_b) {
                 wr.write_cmd_spll(1 << i | 1 << (i + 4));
-                wr.write_cmd_pll(i * 2, pll_data);
+                wr.write_cmd_pll(i * 2, pll_data, size);
             }
             pll_written = true;
         }
diff --git a/libgm/src/Die.cpp b/libgm/src/Die.cpp
index 2761072..390fff2 100644
--- a/libgm/src/Die.cpp
+++ b/libgm/src/Die.cpp
@@ -48,8 +48,26 @@ bool Die::is_ram_data_empty(int x, int y) const { return ram_data.at(std::make_p
 
 bool Die::is_pll_cfg_empty(int index) const
 {
-    int pos = index * 12;
-    for (int i = 0; i < 12; i++)
+    int pos = index * PLL_CFG_SIZE;
+    for (int i = 0; i < PLL_CFG_SIZE; i++)
+        if (pll_cfg[i + pos] != 0x00)
+            return false;
+    return true;
+}
+
+bool Die::is_clkin_cfg_empty() const
+{
+    int pos = PLL_CFG_SIZE * MAX_PLL * 2;
+    for (int i = 0; i < CLKIN_CFG_SIZE; i++)
+        if (pll_cfg[i + pos] != 0x00)
+            return false;
+    return true;
+}
+
+bool Die::is_glbout_cfg_empty() const
+{
+    int pos = PLL_CFG_SIZE * MAX_PLL * 2 + CLKIN_CFG_SIZE;
+    for (int i = 0; i < GLBOUT_CFG_SIZE; i++)
         if (pll_cfg[i + pos] != 0x00)
             return false;
     return true;
@@ -84,18 +102,18 @@ void Die::write_ram_data(int x, int y, const std::vector<uint8_t> &data, uint16_
 
 void Die::write_pll_select(uint8_t select, const std::vector<uint8_t> &data)
 {
-    for (int i = 0; i < 4; i++) {
+    for (int i = 0; i < MAX_PLL; i++) {
         if (select & (1 << i)) {
-            int pos = i * 2 * 12;
+            int pos = i * 2 * PLL_CFG_SIZE;
             if (select & (1 << (i + 4))) {
-                pos += 12;
+                pos += PLL_CFG_SIZE;
             }
-            for (size_t j = 0; j < 12; j++)
+            for (size_t j = 0; j < PLL_CFG_SIZE; j++)
                 pll_cfg[pos++] = data[j];
         }
     }
-    int pos = 8 * 12; // start after PLL data;
-    for (size_t j = 12; j < data.size(); j++)
+    int pos = PLL_CFG_SIZE * MAX_PLL * 2; // start after PLL data;
+    for (size_t j = PLL_CFG_SIZE; j < data.size(); j++)
         pll_cfg[pos++] = data[j];
 }