diff --git a/Makefile b/Makefile
index 46e6b6d..108c2ed 100644
--- a/Makefile
+++ b/Makefile
@@ -18,6 +18,7 @@ build-fonts:
 
 include example/example.mk
 include text_editor/text_editor.mk
+include snake/snake.mk
 include pokemon/pokemon.mk
 
 .PHONY: phony
diff --git a/example/example.mk b/example/example.mk
index 19d5ecc..c19eabc 100644
--- a/example/example.mk
+++ b/example/example.mk
@@ -329,6 +329,19 @@ MAPLE_ANALOG_OBJ = \
 example/maple_analog.elf: LDSCRIPT = $(LIB)/main.lds
 example/maple_analog.elf: $(START_OBJ) $(MAPLE_ANALOG_OBJ)
 
+MAPLE_MOUSE_OBJ = \
+	example/maple_mouse.o \
+	holly/video_output.o \
+	holly/core.o \
+	holly/region_array.o \
+	holly/background.o \
+	holly/ta_fifo_polygon_converter.o \
+	sh7091/serial.o \
+	maple/maple.o
+
+example/maple_mouse.elf: LDSCRIPT = $(LIB)/main.lds
+example/maple_mouse.elf: $(START_OBJ) $(MAPLE_MOUSE_OBJ)
+
 SERIAL_TRANSFER_OBJ = \
 	example/serial_transfer.o \
 	sh7091/serial.o \
diff --git a/example/macaw.cpp b/example/macaw.cpp
index 803ff9a..bf122e2 100644
--- a/example/macaw.cpp
+++ b/example/macaw.cpp
@@ -30,10 +30,10 @@ struct vertex {
 
 const struct vertex strip_vertices[4] = {
   // [ position       ]  [ uv coordinates       ]  [color   ]
-  { -0.5f,   0.5f,  0.f, 0.f        , 127.f/128.f, 0x00000000}, // the first two base colors in a
-  { -0.5f,  -0.5f,  0.f, 0.f        , 0.f        , 0x00000000}, // non-Gouraud triangle strip are ignored
-  {  0.5f,   0.5f,  0.f, 127.f/128.f, 127.f/128.f, 0x00000000},
-  {  0.5f,  -0.5f,  0.f, 127.f/128.f, 0.f        , 0x00000000},
+  { -0.5f,   0.5f,  0.f, 0.f, 1.f, 0x00000000}, // the first two base colors in a
+  { -0.5f,  -0.5f,  0.f, 0.f, 0.f, 0x00000000}, // non-Gouraud triangle strip are ignored
+  {  0.5f,   0.5f,  0.f, 1.f, 1.f, 0x00000000},
+  {  0.5f,  -0.5f,  0.f, 1.f, 0.f, 0x00000000},
 };
 constexpr uint32_t strip_length = (sizeof (strip_vertices)) / (sizeof (struct vertex));
 
diff --git a/example/maple_analog.cpp b/example/maple_analog.cpp
index ac8d926..4257af4 100644
--- a/example/maple_analog.cpp
+++ b/example/maple_analog.cpp
@@ -17,40 +17,36 @@
 #include "holly/background.hpp"
 #include "holly/texture_memory_alloc.hpp"
 #include "memorymap.hpp"
-#include "sh7091/serial.hpp"
 
 #include "geometry/border.hpp"
 #include "geometry/circle.hpp"
 #include "math/vec4.hpp"
 
 #include "maple/maple.hpp"
-#include "maple/maple_impl.hpp"
+#include "maple/maple_host_command_writer.hpp"
 #include "maple/maple_bus_bits.hpp"
 #include "maple/maple_bus_commands.hpp"
 #include "maple/maple_bus_ft0.hpp"
 
-uint32_t _command_buf[(1024 + 32) / 4];
-uint32_t _receive_buf[(1024 + 32) / 4];
-
 static ft0::data_transfer::data_format data[4];
 
-void do_get_condition(uint32_t * command_buf,
-		      uint32_t * receive_buf)
+void do_get_condition()
 {
-  using command_type = get_condition;
-  using response_type = data_transfer<ft0::data_transfer::data_format>;
+  uint32_t send_buf[1024] __attribute__((aligned(32)));
+  uint32_t recv_buf[1024] __attribute__((aligned(32)));
 
-  get_condition::data_fields data_fields = {
-    .function_type = std::byteswap(function_type::controller)
-  };
+  using command_type = maple::get_condition;
+  using response_type = maple::data_transfer<ft0::data_transfer::data_format>;
 
-  const uint32_t command_size = maple::init_host_command_all_ports<command_type, response_type>(command_buf, receive_buf,
-                                                                                        data_fields);
-  using host_response_type = struct maple::host_response<response_type::data_fields>;
-  auto host_response = reinterpret_cast<host_response_type *>(receive_buf);
+  auto writer = maple::host_command_writer(send_buf, recv_buf);
 
-  maple::dma_start(command_buf, command_size,
-                   receive_buf, maple::sizeof_command(host_response));
+  auto [host_command, host_response]
+    = writer.append_command_all_ports<command_type, response_type>();
+
+  host_command->bus_data.data_fields.function_type = std::byteswap(function_type::controller);
+
+  maple::dma_start(send_buf, writer.send_offset,
+                   recv_buf, writer.recv_offset);
 
   for (uint8_t port = 0; port < 4; port++) {
     auto& bus_data = host_response[port].bus_data;
@@ -156,9 +152,6 @@ uint32_t _ta_parameter_buf[((32 * 8192) + 32) / 4];
 
 void main()
 {
-  uint32_t * command_buf = align_32byte(_command_buf);
-  uint32_t * receive_buf = align_32byte(_receive_buf);
-
   video_output::set_mode_vga();
 
   // The address of `ta_parameter_buf` must be a multiple of 32 bytes.
@@ -188,7 +181,7 @@ void main()
   uint32_t frame_ix = 0;
 
   while (1) {
-    do_get_condition(command_buf, receive_buf);
+    do_get_condition();
 
     ta_polygon_converter_init(opb_size.total(),
 			      ta_alloc,
diff --git a/example/maple_mouse.cpp b/example/maple_mouse.cpp
new file mode 100644
index 0000000..900a34c
--- /dev/null
+++ b/example/maple_mouse.cpp
@@ -0,0 +1,247 @@
+#include <cstdint>
+#include <bit>
+
+#include "align.hpp"
+
+#include "holly/video_output.hpp"
+#include "holly/holly.hpp"
+#include "holly/core.hpp"
+#include "holly/core_bits.hpp"
+#include "holly/ta_fifo_polygon_converter.hpp"
+#include "holly/ta_parameter.hpp"
+#include "holly/ta_vertex_parameter.hpp"
+#include "holly/ta_global_parameter.hpp"
+#include "holly/ta_bits.hpp"
+#include "holly/isp_tsp.hpp"
+#include "holly/region_array.hpp"
+#include "holly/background.hpp"
+#include "holly/texture_memory_alloc.hpp"
+#include "memorymap.hpp"
+#include "sh7091/serial.hpp"
+
+#include "geometry/border.hpp"
+#include "geometry/circle.hpp"
+#include "math/vec4.hpp"
+
+#include "maple/maple.hpp"
+#include "maple/maple_host_command_writer.hpp"
+#include "maple/maple_bus_bits.hpp"
+#include "maple/maple_bus_commands.hpp"
+#include "maple/maple_bus_ft0.hpp"
+#include "maple/maple_bus_ft9.hpp"
+
+static ft9::data_transfer::data_format data;
+
+void do_get_condition()
+{
+  uint32_t send_buf[1024] __attribute__((aligned(32)));
+  uint32_t recv_buf[1024] __attribute__((aligned(32)));
+
+  using command_type = maple::get_condition;
+  using response_type = maple::data_transfer<ft9::data_transfer::data_format>;
+
+  auto writer = maple::host_command_writer(send_buf, recv_buf);
+
+  auto [host_command, host_response]
+    = writer.append_command_all_ports<command_type, response_type>();
+
+  host_command->bus_data.data_fields.function_type = std::byteswap(function_type::pointing);
+
+  maple::dma_start(send_buf, writer.send_offset,
+                   recv_buf, writer.recv_offset);
+
+  for (uint8_t port = 0; port < 4; port++) {
+    auto& bus_data = host_response[port].bus_data;
+    if (bus_data.command_code != response_type::command_code) {
+      continue;
+    }
+
+    auto& data_fields = bus_data.data_fields;
+    if ((std::byteswap(data_fields.function_type) & function_type::pointing) == 0) {
+      continue;
+    }
+
+    for (uint32_t i = 0; i < 8; i++) {
+      data.analog_coordinate_axis[i] = data_fields.data.analog_coordinate_axis[i];
+    }
+
+    break;
+  }
+}
+
+void transform(ta_parameter_writer& parameter,
+	       const vec3 * vertices,
+	       const face_vtn& face,
+	       const vec4& color,
+	       const vec3& position,
+	       const float scale
+	       )
+{
+  const uint32_t parameter_control_word = para_control::para_type::polygon_or_modifier_volume
+                                        | para_control::list_type::opaque
+                                        | obj_control::col_type::floating_color
+                                        | obj_control::gouraud;
+
+  const uint32_t isp_tsp_instruction_word = isp_tsp_instruction_word::depth_compare_mode::greater
+                                          | isp_tsp_instruction_word::culling_mode::cull_if_positive;
+
+  const uint32_t tsp_instruction_word = tsp_instruction_word::src_alpha_instr::one
+                                      | tsp_instruction_word::dst_alpha_instr::zero
+                                      | tsp_instruction_word::fog_control::no_fog;
+
+  parameter.append<ta_global_parameter::polygon_type_0>() =
+    ta_global_parameter::polygon_type_0(parameter_control_word,
+					isp_tsp_instruction_word,
+					tsp_instruction_word,
+					0, // texture_control_word
+					0, // data_size_for_sort_dma
+					0  // next_address_for_sort_dma
+					);
+
+  constexpr uint32_t strip_length = 3;
+  for (uint32_t i = 0; i < strip_length; i++) {
+
+    // world transform
+    uint32_t vertex_ix = face[i].vertex;
+    auto& vertex = vertices[vertex_ix];
+    auto point = vertex;
+
+    // rotate 90° around the X axis
+    float x = point.x;
+    float y = point.z;
+    float z = point.y;
+
+    // world transform
+    x *= scale; // world space
+    y *= scale; // world space
+    z *= 10;
+
+    // object transform
+    x += position.x; // object space
+    y += position.y; // object space
+    z += position.z; // object space
+
+    // camera transform
+    z += 1;
+    //y -= 10;
+
+    // screen space transform
+    x *= 240.f;
+    y *= 240.f;
+    x += 320.f;
+    y += 240.f;
+    z = 1 / z;
+
+    bool end_of_strip = i == strip_length - 1;
+
+    parameter.append<ta_vertex_parameter::polygon_type_1>() =
+      ta_vertex_parameter::polygon_type_1(polygon_vertex_parameter_control_word(end_of_strip),
+					  x, y, z,
+					  color.w, // alpha
+					  color.x, // r
+					  color.y, // g
+					  color.z  // b
+					  );
+  }
+}
+
+void init_texture_memory(const struct opb_size& opb_size)
+{
+  region_array2(640 / 32, // width
+                480 / 32, // height
+                opb_size
+                );
+  background_parameter(0xff220000);
+}
+
+uint32_t _ta_parameter_buf[((32 * 8192) + 32) / 4];
+
+void main()
+{
+  video_output::set_mode_vga();
+
+  // The address of `ta_parameter_buf` must be a multiple of 32 bytes.
+  // This is mandatory for ch2-dma to the ta fifo polygon converter.
+  uint32_t * ta_parameter_buf = align_32byte(_ta_parameter_buf);
+
+  constexpr uint32_t ta_alloc = ta_alloc_ctrl::pt_opb::no_list
+			      | ta_alloc_ctrl::tm_opb::no_list
+			      | ta_alloc_ctrl::t_opb::no_list
+			      | ta_alloc_ctrl::om_opb::no_list
+                              | ta_alloc_ctrl::o_opb::_16x4byte;
+
+  constexpr struct opb_size opb_size = { .opaque = 16 * 4
+				       , .opaque_modifier = 0
+				       , .translucent = 0
+				       , .translucent_modifier = 0
+				       , .punch_through = 0
+				       };
+
+  holly.SOFTRESET = softreset::pipeline_soft_reset
+		  | softreset::ta_soft_reset;
+  holly.SOFTRESET = 0;
+
+  core_init();
+  init_texture_memory(opb_size);
+
+  uint32_t frame_ix = 0;
+  float x_pos = 0.0f;
+  float y_pos = 0.0f;
+  float z_pos = 0.0f;
+
+  while (1) {
+    do_get_condition();
+
+    ta_polygon_converter_init(opb_size.total(),
+			      ta_alloc,
+			      640 / 32,
+			      480 / 32);
+
+    x_pos += static_cast<float>(data.analog_coordinate_axis[0] - 0x200) * 0.0015;
+    y_pos += static_cast<float>(data.analog_coordinate_axis[1] - 0x200) * 0.0015;
+    z_pos += static_cast<float>(data.analog_coordinate_axis[2] - 0x200) * 0.015;
+
+    auto parameter = ta_parameter_writer(ta_parameter_buf);
+    for (uint32_t i = 0; i < border::num_faces; i++) {
+      transform(parameter,
+		border::vertices,
+		border::faces[i],
+		{1.0, 0.0, 0.0, 1.0}, // color
+		{0.0, 0.0, 0.0}, // position
+		0.5f * (1.f / 0.95f) // scale
+		);
+    }
+
+    for (uint32_t i = 0; i < circle::num_faces; i++) {
+      transform(parameter,
+		circle::vertices,
+		circle::faces[i],
+		{0.0, 1.0, 1.0, 1.0}, // color
+		{x_pos, y_pos, 0.0}, // position
+		0.05f // scale
+		);
+    }
+
+    for (uint32_t i = 0; i < circle::num_faces; i++) {
+      transform(parameter,
+		circle::vertices,
+		circle::faces[i],
+		{0.0, 1.0, 1.0, 0.0}, // color
+		{1.0, z_pos, 0.0}, // position
+		0.05f // scale
+		);
+    }
+
+    parameter.append<ta_global_parameter::end_of_list>() = ta_global_parameter::end_of_list(para_control::para_type::end_of_list);
+    ta_polygon_converter_transfer(ta_parameter_buf, parameter.offset);
+    ta_wait_opaque_list();
+    core_start_render(frame_ix);
+    core_wait_end_of_render_video();
+
+    while (!spg_status::vsync(holly.SPG_STATUS));
+    core_flip(frame_ix);
+    while (spg_status::vsync(holly.SPG_STATUS));
+
+    frame_ix = (frame_ix + 1) & 1;
+  }
+}
diff --git a/headers.mk b/headers.mk
index 4217714..4a8f766 100644
--- a/headers.mk
+++ b/headers.mk
@@ -62,6 +62,9 @@ maple/maple_bus_ft6_key_scan_codes.hpp: regs/maple_bus_ft6_key_scan_codes.csv re
 maple/maple_bus_ft8.hpp: regs/maple_bus_ft8.csv regs/gen/maple_data_format.py
 	python regs/gen/maple_data_format.py $< > $@
 
+maple/maple_bus_ft9.hpp: regs/maple_bus_ft9.csv regs/gen/maple_data_format.py
+	python regs/gen/maple_data_format.py $< > $@
+
 # AICA
 
 aica/aica_channel.hpp: regs/aica_channel_data.csv regs/gen/aica.py
diff --git a/maple/maple_bus_ft0.hpp b/maple/maple_bus_ft0.hpp
index 999ab82..753a748 100644
--- a/maple/maple_bus_ft0.hpp
+++ b/maple/maple_bus_ft0.hpp
@@ -62,6 +62,7 @@ namespace ft0 {
       uint8_t analog_axis_5;
       uint8_t analog_axis_6;
     };
+    static_assert((sizeof (struct data_format)) % 4 == 0);
     static_assert((sizeof (struct data_format)) == 8);
   }
 
diff --git a/maple/maple_bus_ft6.hpp b/maple/maple_bus_ft6.hpp
index 4026ff1..06ddb8b 100644
--- a/maple/maple_bus_ft6.hpp
+++ b/maple/maple_bus_ft6.hpp
@@ -1,4 +1,5 @@
 #pragma once
+
 namespace ft6 {
   namespace data_transfer {
     namespace modifier_key {
@@ -60,6 +61,7 @@ namespace ft6 {
       uint8_t led_state;
       uint8_t scan_code_array[6];
     };
+    static_assert((sizeof (struct data_format)) % 4 == 0);
     static_assert((sizeof (struct data_format)) == 8);
   }
 
@@ -70,6 +72,7 @@ namespace ft6 {
       uint8_t w2_reserved;
       uint8_t w3_reserved;
     };
+    static_assert((sizeof (struct data_format)) % 4 == 0);
     static_assert((sizeof (struct data_format)) == 4);
   }
 
diff --git a/maple/maple_bus_ft8.hpp b/maple/maple_bus_ft8.hpp
index 8f9c35f..8b34165 100644
--- a/maple/maple_bus_ft8.hpp
+++ b/maple/maple_bus_ft8.hpp
@@ -1,4 +1,5 @@
 #pragma once
+
 namespace ft8 {
   namespace data_transfer {
     namespace vset {
@@ -33,6 +34,7 @@ namespace ft8 {
       uint8_t fm0;
       uint8_t fm1;
     };
+    static_assert((sizeof (struct data_format)) % 4 == 0);
     static_assert((sizeof (struct data_format)) == 4);
   }
 
@@ -43,6 +45,7 @@ namespace ft8 {
       uint8_t freq;
       uint8_t inc;
     };
+    static_assert((sizeof (struct data_format)) % 4 == 0);
     static_assert((sizeof (struct data_format)) == 4);
   }
 
diff --git a/maple/maple_bus_ft9.hpp b/maple/maple_bus_ft9.hpp
new file mode 100644
index 0000000..d2abd1f
--- /dev/null
+++ b/maple/maple_bus_ft9.hpp
@@ -0,0 +1,53 @@
+#pragma once
+
+namespace ft9 {
+  namespace data_transfer {
+    namespace button {
+      constexpr uint32_t r() { return 0b1 << 7; }
+      constexpr uint32_t r(uint32_t reg) { return (reg >> 7) & 0b1; }
+
+      constexpr uint32_t l() { return 0b1 << 6; }
+      constexpr uint32_t l(uint32_t reg) { return (reg >> 6) & 0b1; }
+
+      constexpr uint32_t d() { return 0b1 << 5; }
+      constexpr uint32_t d(uint32_t reg) { return (reg >> 5) & 0b1; }
+
+      constexpr uint32_t u() { return 0b1 << 4; }
+      constexpr uint32_t u(uint32_t reg) { return (reg >> 4) & 0b1; }
+
+      constexpr uint32_t s() { return 0b1 << 3; }
+      constexpr uint32_t s(uint32_t reg) { return (reg >> 3) & 0b1; }
+
+      constexpr uint32_t a() { return 0b1 << 2; }
+      constexpr uint32_t a(uint32_t reg) { return (reg >> 2) & 0b1; }
+
+      constexpr uint32_t b() { return 0b1 << 1; }
+      constexpr uint32_t b(uint32_t reg) { return (reg >> 1) & 0b1; }
+
+      constexpr uint32_t c() { return 0b1 << 0; }
+      constexpr uint32_t c(uint32_t reg) { return (reg >> 0) & 0b1; }
+
+    }
+
+    namespace option {
+      constexpr uint32_t batt() { return 0b1 << 1; }
+      constexpr uint32_t batt(uint32_t reg) { return (reg >> 1) & 0b1; }
+
+      constexpr uint32_t wire() { return 0b1 << 0; }
+      constexpr uint32_t wire(uint32_t reg) { return (reg >> 0) & 0b1; }
+
+    }
+
+    struct data_format {
+      uint8_t button;
+      uint8_t option;
+      uint8_t analog_coordinate_overflow;
+      uint8_t reserved;
+      uint16_t analog_coordinate_axis[8];
+    };
+    static_assert((sizeof (struct data_format)) % 4 == 0);
+    static_assert((sizeof (struct data_format)) == 20);
+  }
+
+}
+
diff --git a/regs/gen/maple_data_format.py b/regs/gen/maple_data_format.py
index 2716745..b084dd1 100644
--- a/regs/gen/maple_data_format.py
+++ b/regs/gen/maple_data_format.py
@@ -28,6 +28,8 @@ def parse_bits(bits: list[str]):
     bit_order = [7, 6, 5, 4, 3, 2, 1, 0]
     by_name = defaultdict(list)
     for bit_ix, bit in zip(bit_order, bits):
+        if bit == '':
+            continue
         by_name[bit].append(bit_ix)
     for name, indicies in by_name.items():
         yield Bit(name=name,
@@ -65,8 +67,8 @@ def parse_data_format(ix, rows):
         ix += 1
         excess_bits = [b for b in _bits[8:] if b != ""]
         assert excess_bits == []
-        bits = [b for b in _bits[:8] if b != ""]
-        assert len(bits) in {0, 8}, bits
+        bits = [b for b in _bits[:8]]
+        assert len(bits) == 8, bits
         fields[field_name].append(Field(field_name,
                                         list(parse_bits(bits))))
         _, variable = parse_format_name(field_name)
@@ -126,6 +128,9 @@ def render_format(format):
             yield f"uint16_t {field_name};"
         elif len(subfields) in {3, 6}:
             yield f"uint8_t {field_name}[{len(subfields)}];"
+        elif len(subfields) == 16:
+            # bleh: hacky
+            yield f"uint16_t {field_name}[8];"
         elif len(subfields) == 4:
             yield f"uint32_t {field_name};"
         else:
diff --git a/regs/maple_bus_ft9.csv b/regs/maple_bus_ft9.csv
new file mode 100644
index 0000000..a24c916
--- /dev/null
+++ b/regs/maple_bus_ft9.csv
@@ -0,0 +1,21 @@
+"data_transfer",7,6,5,4,3,2,1,0
+"button","r","l","d","u","s","a","b","c"
+"option",,,,,,,"batt","wire"
+"analog_coordinate_overflow",,,,,,,,
+"reserved",,,,,,,,
+"analog_coordinate_axis",,,,,,,,
+"analog_coordinate_axis",,,,,,,,
+"analog_coordinate_axis",,,,,,,,
+"analog_coordinate_axis",,,,,,,,
+"analog_coordinate_axis",,,,,,,,
+"analog_coordinate_axis",,,,,,,,
+"analog_coordinate_axis",,,,,,,,
+"analog_coordinate_axis",,,,,,,,
+"analog_coordinate_axis",,,,,,,,
+"analog_coordinate_axis",,,,,,,,
+"analog_coordinate_axis",,,,,,,,
+"analog_coordinate_axis",,,,,,,,
+"analog_coordinate_axis",,,,,,,,
+"analog_coordinate_axis",,,,,,,,
+"analog_coordinate_axis",,,,,,,,
+"analog_coordinate_axis",,,,,,,,
diff --git a/regs/maple_bus_ft9.ods b/regs/maple_bus_ft9.ods
new file mode 100644
index 0000000..1184608
Binary files /dev/null and b/regs/maple_bus_ft9.ods differ