diff --git a/base/base.h b/base/base.h
index 86fdeb0..12e73e3 100644
--- a/base/base.h
+++ b/base/base.h
@@ -35,6 +35,10 @@ inline void clear_pin(io_pin_t *pin) {
     *(pin->port) &= ~(_BV(pin->addr));
 }
 
+inline int read_pin(io_pin_t *pin) {
+    return (*(pin->port) & _BV(pin->addr)) > 0;
+}
+
 typedef struct RNG {
     uint8_t mod;
     int8_t a;
diff --git a/flake.nix b/flake.nix
index e756f68..5d3f716 100644
--- a/flake.nix
+++ b/flake.nix
@@ -49,7 +49,7 @@
           includes = [ "base" "morse" ];
 
           MCU = "atmega32u4";
-          CHIP_SELECT = "AVR_ATmego32u4";
+          CHIP_SELECT = "AVR_ATmega32u4";
           F_CPU = "8000000";
           CFLAGS = ''-O -finline-functions -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums -Wall -Wstrict-prototypes -DF_CPU=${F_CPU} -std=gnu99 -D__${CHIP_SELECT}__=1 -mmcu=${MCU} -DAVR=1'';
           INCLUDE_DIRS = lib.concatStringsSep " " (map (dir: "-I${src}/${dir}") includes);
@@ -66,6 +66,34 @@
             '';
         };
 
+      packages."x86_64-linux"."spi_test" =
+        let
+          pkgs = import nixpkgs { system = "x86_64-linux"; };
+          lib = pkgs.lib;
+          avr = pkgs.pkgsCross.avr.buildPackages;
+        in pkgs.stdenv.mkDerivation rec {
+          name = "morse-tx";
+          src = ./.;
+
+          includes = [ "base" "spi" ];
+
+          MCU = "atmega32u4";
+          CHIP_SELECT = "AVR_ATmega32u4";
+          F_CPU = "8000000";
+          CFLAGS = ''-O -finline-functions -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums -Wall -Wstrict-prototypes -DF_CPU=${F_CPU} -std=gnu99 -D__${CHIP_SELECT}__=1 -mmcu=${MCU} -DAVR=1'';
+          INCLUDE_DIRS = lib.concatStringsSep " " (map (dir: "-I${src}/${dir}") includes);
+
+          buildPhase = ''
+            ${avr.gcc}/bin/avr-gcc ${CFLAGS} ${INCLUDE_DIRS} -o spi.o -c ${src}/spi/spi.c
+            ${avr.gcc}/bin/avr-gcc ${CFLAGS} ${INCLUDE_DIRS} -o main.o -c ${src}/spi_test/main.c
+            ${avr.gcc}/bin/avr-gcc ${CFLAGS} -o main.elf main.o spi.o
+            $OBJCOPY -O ihex main.elf main.hex
+            '';
+          installPhase = ''
+            mkdir $out
+            cp main.elf main.hex $out
+            '';
+        };
 
       devShell."x86_64-linux" =
         let
diff --git a/spi/spi.c b/spi/spi.c
new file mode 100644
index 0000000..ca4d95d
--- /dev/null
+++ b/spi/spi.c
@@ -0,0 +1,42 @@
+
+#include <spi.h>
+#include <util/delay.h>
+
+void initialize_spi(spi_t *spi) {
+    set_pin_direction(&spi->clock, PIN_OUT);
+    set_pin_direction(&spi->data_out, PIN_OUT);
+    set_pin_direction(&spi->data_in, PIN_IN);
+    set_pin_direction(&spi->chip_select, PIN_OUT);
+}
+
+uint8_t transfer_byte(spi_t *spi, uint8_t output) {
+    uint8_t input = 0;
+    int input_bit;
+
+    set_pin(&spi->chip_select);
+
+    for (int i = 7; i >= 0; i--) {
+        clear_pin(&spi->clock);
+        if (output & _BV(i)) {
+            set_pin(&spi->data_out);
+        } else {
+            clear_pin(&spi->data_out);
+        }
+        _delay_us(10);
+        set_pin(&spi->clock);
+        _delay_us(10);
+        //input_bit = read_pin(&spi->data_in);
+        //input <<= input_bit;
+    }
+    clear_pin(&spi->clock);
+    _delay_us(10);
+    clear_pin(&spi->chip_select);
+    return input;
+}
+
+/*
+void send_bytes(spi_t *line, u8 *byte, size_t length, u8 *input, size_t input_length) {
+
+}
+*/
+
diff --git a/spi/spi.h b/spi/spi.h
new file mode 100644
index 0000000..6a090eb
--- /dev/null
+++ b/spi/spi.h
@@ -0,0 +1,18 @@
+
+#ifndef __MORSE_H__
+#define __MORSE_H__
+
+#include <base.h>
+#include <stdlib.h>
+
+typedef struct SPI {
+    io_pin_t clock;
+    io_pin_t data_out;
+    io_pin_t data_in;
+    io_pin_t chip_select;
+} spi_t;
+
+void initialize_spi(spi_t *spi);
+uint8_t transfer_byte(spi_t *spi, uint8_t output);
+
+#endif
diff --git a/spi_test/main.c b/spi_test/main.c
new file mode 100644
index 0000000..4d203e6
--- /dev/null
+++ b/spi_test/main.c
@@ -0,0 +1,36 @@
+#include <avr/io.h>
+#include <util/delay.h>
+#include <base.h>
+#include <spi.h>
+
+int main(void) {
+    spi_t spi = (spi_t){
+        .clock          = { .ddr = &DDRF, .port = &PORTF, .addr = 7 },
+        .data_out       = { .ddr = &DDRF, .port = &PORTF, .addr = 6 },
+        .data_in        = { .ddr = &DDRF, .port = &PORTF, .addr = 5 },
+        .chip_select    = { .ddr = &DDRF, .port = &PORTF, .addr = 4 },
+    };
+
+    io_pin_t light = { .ddr = &DDRC, .port = &PORTC, .addr = 7 };
+
+    initialize_spi(&spi);
+
+    while (1) {
+        set_pin(&light);
+        transfer_byte(&spi, 0xaa);
+        _delay_ms(1000);
+        clear_pin(&light);
+        _delay_ms(1000);
+    }
+
+    /*
+    while(1) {
+        set_pin(&spi.clock);
+        set_pin(&spi.data_out);
+        _delay_ms(500);
+        clear_pin(&spi.clock);
+        clear_pin(&spi.data_out);
+        _delay_ms(500);
+    }
+    */
+}