diff --git a/flake.nix b/flake.nix
index 3c6f32a..63c6886 100644
--- a/flake.nix
+++ b/flake.nix
@@ -34,7 +34,12 @@
                   ${gcc} ${cflags} ${include_dirs} -c $source
               fi
           done
-          cp ${src}/*.h . || true
+          for source in ${src}/src/*.c; do
+              if [ -e $source ]; then
+                  ${gcc} ${cflags} ${include_dirs} -c $source
+              fi
+          done
+          cp ${src}/*.h ${src}/src/*.h . || true
           '';
 
         installPhase = ''
@@ -44,15 +49,16 @@
           '';
       };
 
-      mkProgram = { pkgs, gcc, cflags, pname, psrc, pbuildInputs ? [] }:
+      mkProgram = { pkgs, gcc, cflags, pname, psrc, pbuildInputs ? [], pnativeBuildInputs ? [] }:
       pkgs.stdenv.mkDerivation rec {
         name = pname;
         src = psrc;
 
         buildInputs = pbuildInputs;
+        nativeBuildInputs = pnativeBuildInputs;
 
-        include_dirs = pkgs.lib.concatStringsSep " " (map (dir: "-I${dir}/include") buildInputs);
-        object_files = pkgs.lib.concatStringsSep " " (map (dir: "${dir}/lib/*.o") buildInputs);
+        include_dirs = pkgs.lib.concatStringsSep " " (map (dir: "-I${dir}/include") pbuildInputs);
+        object_files = pkgs.lib.concatStringsSep " " (map (dir: "${dir}/lib/*.o") pbuildInputs);
 
         dontUnpack = true;
         dontConfigure = true;
@@ -73,6 +79,35 @@
           '';
       };
 
+      mkTests = { pkgs, gcc, cflags, pname, psrc, pbuildInputs ? [], pnativeBuildInputs ? [] }:
+      pkgs.stdenv.mkDerivation rec {
+        name = pname;
+        src = psrc;
+
+        buildInputs = pbuildInputs;
+        nativeBuildInputs = pnativeBuildInputs;
+
+        include_dirs = pkgs.lib.concatStringsSep " " (map (dir: "-I${dir}/include") buildInputs);
+        object_files = pkgs.lib.concatStringsSep " " (map (dir: "${dir}/lib/*.o") buildInputs);
+
+        dontUnpack = true;
+        dontConfigure = true;
+
+        buildPhase = ''
+          for source in ${src}/tests/*.c; do
+              if [ -e $source ]; then
+                  ${gcc} ${cflags} ${include_dirs} -c $source
+              fi
+          done
+
+          ${gcc} -o ${name} ${cflags} ${object_files} *.o
+          '';
+
+        installPhase = ''
+          mkdir -p $out/bin
+          cp ${name} $out/bin
+          '';
+      };
 
     in rec
     {
@@ -85,7 +120,8 @@
           paths = [
             (packages."x86_64-linux"."prime-tx" { gcc = "${avr.gcc}/bin/avr-gcc"; cflags = mcu_cflags atmega32u4; })
             (packages."x86_64-linux"."radio-rx" { gcc = "${avr.gcc}/bin/avr-gcc"; cflags = mcu_cflags atmega32u4; })
-            (packages."x86_64-linux"."packet-radio" { gcc = "${avr.gcc}/bin/avr-gcc"; cflags = mcu_cflags atmega32u4; })
+            (packages."x86_64-linux"."packet-radio" { gcc = "${avr.gcc}/bin/avr-gcc"; cflags = "-Wall -Werror"; })
+            (packages."x86_64-linux"."packet-radio-tests" { gcc = "${avr.gcc}/bin/avr-gcc"; cflags = "-Wall -Werror"; })
           ];
         };
 
@@ -202,6 +238,11 @@
           ];
         };
 
+      packages."x86_64-linux"."packet-radio_" =
+        let
+          pkgs = import nixpkgs { system = "x86_64-linux"; };
+        in packages."x86_64-linux"."packet-radio" { gcc = "${pkgs.gcc}/bin/gcc"; cflags = "-Wall -Werror"; };
+
       packages."x86_64-linux"."packet-radio" =
         { gcc, cflags }:
         let
@@ -210,11 +251,31 @@
           pkgs = pkgs;
           gcc = gcc;
           cflags = cflags;
-          pname = "display";
-          psrc = ./display;
+          pname = "packet-radio";
+          psrc = ./packet-radio;
+          pbuildInputs = [ ];
+        };
+
+      packages."x86_64-linux"."packet-radio-tests_" =
+        let
+          pkgs = import nixpkgs { system = "x86_64-linux"; };
+        in packages."x86_64-linux"."packet-radio-tests" { gcc = "${pkgs.gcc}/bin/gcc"; cflags = "-Wall -Werror -lcriterion"; };
+
+      packages."x86_64-linux"."packet-radio-tests" =
+        { gcc, cflags }:
+        let
+          pkgs = import nixpkgs { system = "x86_64-linux"; };
+        in mkTests {
+          pkgs = pkgs;
+          gcc = gcc;
+          cflags = cflags;
+          pname = "packet-radio-tests";
+          psrc = ./packet-radio;
           pbuildInputs = [
-            (packages."x86_64-linux"."dio" { inherit gcc cflags; })
-            (packages."x86_64-linux"."shift-register" { inherit gcc cflags; })
+            (packages."x86_64-linux"."packet-radio" { inherit gcc cflags; })
+          ];
+          pnativeBuildInputs = [
+            pkgs.criterion
           ];
         };
 
@@ -266,6 +327,7 @@
             avrdude
             simavr
             gtkwave
+            criterion
           ];
         in
         pkgs.mkShell {
diff --git a/packet-radio/src/packet.h b/packet-radio/src/packet.h
new file mode 100644
index 0000000..7f1bfc6
--- /dev/null
+++ b/packet-radio/src/packet.h
@@ -0,0 +1,28 @@
+
+#ifndef __PACKET_H__
+#define __PACKET_H__
+
+#ifdef __AVR__
+
+#else
+#include <stdint.h>
+#include <stdbool.h>
+#endif
+
+typedef enum {
+    packet_type_data,
+    packet_type_ack,
+    packet_type_retry,
+} packet_type_e;
+
+typedef struct {
+    packet_type_e type;
+    uint16_t count;
+    uint8_t sender;
+    uint8_t receiver;
+    size_t length;
+    char message[60];
+} packet_t;
+
+#endif
+
diff --git a/packet-radio/src/packet_buffer.c b/packet-radio/src/packet_buffer.c
new file mode 100644
index 0000000..1b66466
--- /dev/null
+++ b/packet-radio/src/packet_buffer.c
@@ -0,0 +1,62 @@
+
+#include "radio.h"
+#include "packet.h"
+#include "packet_buffer.h"
+#include <string.h>
+
+size_t circular_next(size_t current, size_t max);
+
+packet_buffer_t *packet_buffer_new() {
+    return malloc(sizeof(packet_buffer_t));
+}
+
+packet_t *packet_buffer_enqueue(packet_buffer_t *self, packet_buffer_status_e *status) {
+    if (!IS_OK(status)) return NULL;
+
+    if (packet_buffer_is_full(self)) {
+        *status = packet_buffer_status_full;
+        return NULL;
+    }
+
+    packet_t *ptr = &self->buffer[self->top];
+    self->top = circular_next(self->top, 5);
+    self->count++;
+    return ptr;
+}
+
+packet_t *packet_buffer_head(packet_buffer_t *self, packet_buffer_status_e *status) {
+    if (!IS_OK(status)) return NULL;
+
+    if (packet_buffer_is_empty(self)) {
+        *status = packet_buffer_status_empty;
+        return NULL;
+    }
+
+    return &self->buffer[self->bottom];
+}
+
+void packet_buffer_dequeue(packet_buffer_t *self, packet_buffer_status_e *status) {
+    if (!IS_OK(status)) return;
+
+    if (packet_buffer_is_empty(self)) {
+        *status = packet_buffer_status_empty;
+        return;
+    }
+
+    self->bottom = circular_next(self->bottom, 5);
+    self->count--;
+}
+
+bool packet_buffer_is_full(packet_buffer_t *self) {
+    return self->count == 5;
+}
+
+bool packet_buffer_is_empty(packet_buffer_t *self) {
+    return self->count == 0;
+}
+
+size_t circular_next(size_t current, size_t max) {
+    current++;
+    return (current < max) ? current : 0;
+}
+
diff --git a/packet-radio/src/packet_buffer.h b/packet-radio/src/packet_buffer.h
new file mode 100644
index 0000000..c7320de
--- /dev/null
+++ b/packet-radio/src/packet_buffer.h
@@ -0,0 +1,30 @@
+
+#ifndef __PACKET_BUFFER_H__
+#define __PACKET_BUFFER_H__
+
+#include "packet.h"
+#include <stdlib.h>
+
+typedef enum {
+    packet_buffer_status_ok,
+    packet_buffer_status_empty,
+    packet_buffer_status_full,
+} packet_buffer_status_e;
+
+typedef struct {
+    size_t count;
+    size_t bottom;
+    size_t top;
+    packet_t buffer[5];
+} packet_buffer_t;
+
+packet_buffer_t *packet_buffer_new();
+
+packet_t * packet_buffer_enqueue(packet_buffer_t *, packet_buffer_status_e *);
+packet_t * packet_buffer_head(packet_buffer_t *, packet_buffer_status_e *);
+void packet_buffer_dequeue(packet_buffer_t *, packet_buffer_status_e *);
+
+bool packet_buffer_is_full(packet_buffer_t *);
+bool packet_buffer_is_empty(packet_buffer_t *);
+
+#endif
diff --git a/packet-radio/radio.c b/packet-radio/src/radio.c
similarity index 61%
rename from packet-radio/radio.c
rename to packet-radio/src/radio.c
index 5f7561c..b5b3937 100644
--- a/packet-radio/radio.c
+++ b/packet-radio/src/radio.c
@@ -1,39 +1,28 @@
 
 #include "radio.h"
+#include "packet.h"
 #include <string.h>
 #include <stdlib.h>
 
-typedef enum {
-    data,
-    ack,
-    retry,
-} packet_type_e;
-
 typedef struct {
     bool packet_sent;
     bool packet_ready;
 } flags_t;
 
-typedef struct {
-    packet_type_e type;
-    uint16_t count;
-    uint8_t sender;
-    uint8_t receiver;
-    size_t size;
-    char message[60];
-} packet_t;
-
 struct conn_s {
     uint16_t packet_counter;
     uint8_t address;
 
-    packet_t outgoing_buffer[5];
-    size_t outgoing_bottom;
-    size_t outgoing_top;
+    // packet_buffer_t outgoing_packets;
+    // packet_buffer_t incoming_packets;
 
-    packet_t incoming_buffer[5];
-    size_t incoming_bottom;
-    size_t incoming_top;
+    // packet_t outgoing_buffer[5];
+    // size_t outgoing_bottom;
+    // size_t outgoing_top;
+
+    // packet_t incoming_buffer[5];
+    // size_t incoming_bottom;
+    // size_t incoming_top;
 
     void (*set_mode)(void *, radio_mode_e, radio_status_e *);
     flags_t (*get_flags)(void *, radio_status_e *);
@@ -45,16 +34,21 @@ struct conn_s {
 
 
 void conn_set_address(conn_t *self, uint8_t addr, radio_status_e *status) {
+    /*
     if (!IS_OK(status)) return;
     self->address = addr;
+    */
 }
 
 void conn_set_mode(conn_t *self, radio_mode_e mode, radio_status_e *status) {
+    /*
     if (!IS_OK(status)) return;
     self->set_mode(self->radio, mode, status);
+    */
 }
 
 void conn_send(conn_t *self, uint8_t dest, msg_t *message, radio_status_e *status) {
+    /*
     if (!IS_OK(status)) return;
 
     if (message->length > MAX_MESSAGE_LENGTH) {
@@ -78,9 +72,11 @@ void conn_send(conn_t *self, uint8_t dest, msg_t *message, radio_status_e *statu
     if (IS_OK(status)) self->outgoing_top++;
 
     return;
+    */
 }
 
 received_msg_t * conn_receive(conn_t *self, radio_status_e *status) {
+    /*
     if (!IS_OK(status)) return NULL;
 
     if (self->incoming_bottom == self->incoming_top) {
@@ -96,18 +92,50 @@ received_msg_t * conn_receive(conn_t *self, radio_status_e *status) {
     self->incoming_bottom++;
 
     return msg;
+    */
+    return NULL;
 }
 
 void conn_handle_interrupt(conn_t *self) {
+    /*
     radio_status_e *status = ok;
 
     flags_t flags = self->get_flags(self->radio, status);
+    // if this is failing, we should raise a flag that indicates that the radio itself is in trouble
     if (!IS_OK(status)) return;
 
     if (flags.packet_ready) {
         uint8_t data[66];
         self->receive(self->radio, data, status);
+        // if this fails, increment an error counter
         if (!IS_OK(status)) return;
+
+        packet_t *packet = (packet_t *)data;
+        if (packet->receiver != self->address) {
+            return;
+        }
+
+        switch (packet->type) {
+            case packet_type_data:
+                memcpy(self->incoming_buffer[self->incoming_top], packet, packet->size);
+                self->incoming_top++;
+                break;
+            case packet_type_ack:
+                uint16_t confirmed = packet->data[0] << 8 + packet->data[1];
+                while (self->outgoing_buffer[self->outgoing_bottom]->count < confirmed && !is_empty(self->outgoing_buffer)
+                break;
+            case packet_type_retry:
+                break;
+        }
+        // process the packet type
+        // break;
     }
+
+    // timeout processing
+    // if (time > receiving_timeout) { }
+    // if we were receiving data, a receiving_timeout must have been set. At this point, we're not receiving any more data, so it's time to send a confirmation.
+    // if (time > confirmation_timeout) { }
+    // if we were sending data, a confirmation timeout must have been set. But I don't recall what this is good for? Do we want to retransmit everything?
+    */
 }
 
diff --git a/packet-radio/radio.h b/packet-radio/src/radio.h
similarity index 100%
rename from packet-radio/radio.h
rename to packet-radio/src/radio.h
diff --git a/packet-radio/tests/packet-buffer.c b/packet-radio/tests/packet-buffer.c
new file mode 100644
index 0000000..1d15768
--- /dev/null
+++ b/packet-radio/tests/packet-buffer.c
@@ -0,0 +1,167 @@
+#include <criterion/criterion.h>
+#include <stdio.h>
+#include "packet_buffer.h"
+
+Test(packet_buffer, empty_buffer) {
+    packet_buffer_t *buffer = packet_buffer_new();
+    cr_assert(packet_buffer_is_empty(buffer));
+    cr_assert(!packet_buffer_is_full(buffer));
+}
+
+Test(packet_buffer, full_buffer) {
+    packet_buffer_status_e status = packet_buffer_status_ok;
+    packet_buffer_t *buffer = packet_buffer_new();
+    packet_t *packet;
+
+    packet = packet_buffer_enqueue(buffer, &status);
+    cr_assert(packet != NULL);
+    cr_assert(status == packet_buffer_status_ok);
+    cr_assert(!packet_buffer_is_empty(buffer));
+    cr_assert(!packet_buffer_is_full(buffer));
+
+    packet = packet_buffer_enqueue(buffer, &status);
+    cr_assert(packet != NULL);
+    cr_assert(status == packet_buffer_status_ok);
+
+    packet = packet_buffer_enqueue(buffer, &status);
+    cr_assert(packet != NULL);
+    cr_assert(status == packet_buffer_status_ok);
+
+    packet = packet_buffer_enqueue(buffer, &status);
+    cr_assert(packet != NULL);
+    cr_assert(status == packet_buffer_status_ok);
+
+    packet = packet_buffer_enqueue(buffer, &status);
+    cr_assert(packet != NULL);
+    cr_assert(status == packet_buffer_status_ok);
+    cr_assert(packet_buffer_is_full(buffer));
+
+    packet = packet_buffer_enqueue(buffer, &status);
+    cr_assert(packet == NULL);
+    cr_assert(status == packet_buffer_status_full);
+    cr_assert(packet_buffer_is_full(buffer));
+}
+
+Test(packet_buffer, basic_enqueue_and_dequeue) {
+    packet_buffer_status_e status = packet_buffer_status_ok;
+    packet_buffer_t *buffer = packet_buffer_new();
+    packet_t *packet;
+
+    packet = packet_buffer_enqueue(buffer, &status);
+    cr_assert(status == packet_buffer_status_ok);
+
+    packet->type = packet_type_data;
+    packet->count = 0;
+    packet->sender = 15;
+    packet->receiver = 16;
+    packet->length = 2;
+    memcpy(packet->message, (char [2]){ 25, 24 }, 2);
+
+    packet = packet_buffer_head(buffer, &status);
+    cr_assert(status == packet_buffer_status_ok);
+    cr_assert(packet->type == packet_type_data);
+    cr_assert(packet->count == 0);
+    cr_assert(packet->sender == 15);
+    cr_assert(packet->receiver == 16);
+    cr_assert(packet->length == 2);
+    cr_assert(packet->message[0] == 25);
+    cr_assert(packet->message[1] == 24);
+
+    packet_buffer_dequeue(buffer, &status);
+    cr_assert(status == packet_buffer_status_ok);
+}
+
+Test(packet_buffer, enqueue_to_full) {
+    packet_buffer_status_e status = packet_buffer_status_ok;
+    packet_buffer_t *buffer = packet_buffer_new();
+    packet_t *packet;
+
+    packet = packet_buffer_enqueue(buffer, &status);
+    cr_assert(status == packet_buffer_status_ok);
+
+    packet->type = packet_type_data;
+    packet->count = 0;
+    packet->sender = 15;
+    packet->receiver = 16;
+    packet->length = 2;
+    memcpy(packet->message, (char [2]){ 25, 24 }, 2);
+
+    packet = packet_buffer_enqueue(buffer, &status);
+    packet = packet_buffer_enqueue(buffer, &status);
+    packet = packet_buffer_enqueue(buffer, &status);
+    packet = packet_buffer_enqueue(buffer, &status);
+    cr_assert(status == packet_buffer_status_ok);
+
+    packet = packet_buffer_head(buffer, &status);
+    cr_assert(status == packet_buffer_status_ok);
+    cr_assert(packet->type == packet_type_data);
+    cr_assert(packet->count == 0);
+    cr_assert(packet->sender == 15);
+    cr_assert(packet->receiver == 16);
+    cr_assert(packet->length == 2);
+    cr_assert(packet->message[0] == 25);
+    cr_assert(packet->message[1] == 24);
+
+    packet_buffer_dequeue(buffer, &status);
+    cr_assert(status == packet_buffer_status_ok);
+}
+
+Test(packet_buffer, circular_buffer) {
+    packet_buffer_status_e status = packet_buffer_status_ok;
+    packet_buffer_t *buffer = packet_buffer_new();
+    packet_t *packet;
+
+    packet = packet_buffer_enqueue(buffer, &status);
+    packet = packet_buffer_enqueue(buffer, &status);
+    packet = packet_buffer_enqueue(buffer, &status);
+    packet->type = packet_type_data;
+    packet->count = 0;
+    packet->sender = 15;
+    packet->receiver = 16;
+    packet->length = 2;
+    memcpy(packet->message, (char [2]){ 25, 24 }, 2);
+
+    packet_buffer_dequeue(buffer, &status);
+    packet_buffer_dequeue(buffer, &status);
+
+    packet = packet_buffer_enqueue(buffer, &status);
+    packet = packet_buffer_enqueue(buffer, &status);
+    packet = packet_buffer_enqueue(buffer, &status);
+    packet = packet_buffer_enqueue(buffer, &status);
+    cr_assert(status == packet_buffer_status_ok);
+
+    packet->type = packet_type_data;
+    packet->count = 1;
+    packet->sender = 15;
+    packet->receiver = 16;
+    packet->length = 2;
+    memcpy(packet->message, (char [2]){ 25, 24 }, 2);
+
+    packet = packet_buffer_head(buffer, &status);
+    cr_assert(status == packet_buffer_status_ok);
+    cr_assert(packet->type == packet_type_data);
+    cr_assert(packet->count == 0);
+    cr_assert(packet->sender == 15);
+    cr_assert(packet->receiver == 16);
+    cr_assert(packet->length == 2);
+    cr_assert(packet->message[0] == 25);
+    cr_assert(packet->message[1] == 24);
+
+    packet_buffer_dequeue(buffer, &status);
+    packet_buffer_dequeue(buffer, &status);
+    packet_buffer_dequeue(buffer, &status);
+    packet_buffer_dequeue(buffer, &status);
+    packet = packet_buffer_head(buffer, &status);
+    cr_assert(status == packet_buffer_status_ok);
+    cr_assert(packet->type == packet_type_data);
+    cr_assert(packet->count == 1);
+    cr_assert(packet->sender == 15);
+    cr_assert(packet->receiver == 16);
+    cr_assert(packet->length == 2);
+    cr_assert(packet->message[0] == 25);
+    cr_assert(packet->message[1] == 24);
+
+    packet_buffer_dequeue(buffer, &status);
+    cr_assert(status == packet_buffer_status_ok);
+    cr_assert(packet_buffer_is_empty(buffer));
+}