10 files changed, 301 insertions, 140 deletions

diff --git a/keyboards/massdrop/alt/config.h b/keyboards/massdrop/alt/config.h
index d28094c49..085e1aebb 100644
--- a/keyboards/massdrop/alt/config.h
+++ b/keyboards/massdrop/alt/config.h
@@ -50,22 +50,18 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 /* This Shift Register expands available hardware output lines to control additional peripherals */
 /* It uses four lines from the MCU to provide 16 output lines */
 /* Shift Register Clock configuration (MCU to ShiftRegister.RCLK) */
-#define SR_EXP_RCLK_PORT            PB
-#define SR_EXP_RCLK_PIN             14
+#define SR_EXP_RCLK_PIN          B14
 /* Shift Register Output Enable configuration (MCU to ShiftRegister.OE_N) */
-#define SR_EXP_OE_N_PORT            PB
-#define SR_EXP_OE_N_PIN             15
+#define SR_EXP_OE_PIN            B15
 /* SERCOM port to use for Shift Register SPI */
 /* DATAOUT and SCLK must be configured to use hardware pins of this port */
-#define SR_EXP_SERCOM               SERCOM2
+#define SPI_SERCOM               SERCOM2
 /* Shift Register SPI Data Out configuration (MCU.SERCOMx.PAD[0] to ShiftRegister.SER) */
-#define SR_EXP_DATAOUT_PORT         PA
-#define SR_EXP_DATAOUT_PIN          12
-#define SR_EXP_DATAOUT_MUX          2
+#define SPI_DATAOUT_PIN          A12
+#define SPI_DATAOUT_MUX          2
 /* Shift Register SPI Serial Clock configuration (MCU.SERCOMx.PAD[1] to ShiftRegister.SRCLK) */
-#define SR_EXP_SCLK_PORT            PA
-#define SR_EXP_SCLK_PIN             13
-#define SR_EXP_SCLK_MUX             2
+#define SPI_SCLK_PIN             A13
+#define SPI_SCLK_MUX             2
 
 /* Debug LED (Small LED Located near MCU) */
 #define DEBUG_LED_ENABLE            1
diff --git a/keyboards/massdrop/ctrl/config.h b/keyboards/massdrop/ctrl/config.h
index 3dbd9b887..aefb90044 100644
--- a/keyboards/massdrop/ctrl/config.h
+++ b/keyboards/massdrop/ctrl/config.h
@@ -49,22 +49,18 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 /* This Shift Register expands available hardware output lines to control additional peripherals */
 /* It uses four lines from the MCU to provide 16 output lines */
 /* Shift Register Clock configuration (MCU to ShiftRegister.RCLK) */
-#define SR_EXP_RCLK_PORT            PB
-#define SR_EXP_RCLK_PIN             14
+#define SR_EXP_RCLK_PIN          B14
 /* Shift Register Output Enable configuration (MCU to ShiftRegister.OE_N) */
-#define SR_EXP_OE_N_PORT            PB
-#define SR_EXP_OE_N_PIN             15
+#define SR_EXP_OE_PIN            B15
 /* SERCOM port to use for Shift Register SPI */
 /* DATAOUT and SCLK must be configured to use hardware pins of this port */
-#define SR_EXP_SERCOM               SERCOM2
+#define SPI_SERCOM               SERCOM2
 /* Shift Register SPI Data Out configuration (MCU.SERCOMx.PAD[0] to ShiftRegister.SER) */
-#define SR_EXP_DATAOUT_PORT         PA
-#define SR_EXP_DATAOUT_PIN          12
-#define SR_EXP_DATAOUT_MUX          2
+#define SPI_DATAOUT_PIN          A12
+#define SPI_DATAOUT_MUX          2
 /* Shift Register SPI Serial Clock configuration (MCU.SERCOMx.PAD[1] to ShiftRegister.SRCLK) */
-#define SR_EXP_SCLK_PORT            PA
-#define SR_EXP_SCLK_PIN             13
-#define SR_EXP_SCLK_MUX             2
+#define SPI_SCLK_PIN             A13
+#define SPI_SCLK_MUX             2
 
 /* Debug LED (Small LED Located near MCU) */
 #define DEBUG_LED_ENABLE            1
diff --git a/tmk_core/common/arm_atsam/gpio.h b/tmk_core/common/arm_atsam/gpio.h
index c2d5a3088..915ed0ef4 100644
--- a/tmk_core/common/arm_atsam/gpio.h
+++ b/tmk_core/common/arm_atsam/gpio.h
@@ -64,7 +64,13 @@ typedef uint8_t pin_t;
         PORT->Group[SAMD_PORT(pin)].OUTCLR.reg = SAMD_PIN_MASK(pin); \
     } while (0)
 
-#define writePin(pin, level) ((level) ? (writePinHigh(pin)) : (writePinLow(pin)))
+#define writePin(pin, level)                                             \
+    do {                                                                 \
+        if (level)                                                       \
+            PORT->Group[SAMD_PORT(pin)].OUTSET.reg = SAMD_PIN_MASK(pin); \
+        else                                                             \
+            PORT->Group[SAMD_PORT(pin)].OUTCLR.reg = SAMD_PIN_MASK(pin); \
+    } while (0)
 
 #define readPin(pin) ((PORT->Group[SAMD_PORT(pin)].IN.reg & SAMD_PIN_MASK(pin)) != 0)
 
diff --git a/tmk_core/protocol/arm_atsam.mk b/tmk_core/protocol/arm_atsam.mk
index 5bb45d658..e3b550596 100644
--- a/tmk_core/protocol/arm_atsam.mk
+++ b/tmk_core/protocol/arm_atsam.mk
@@ -9,7 +9,8 @@ ifeq ($(RGB_MATRIX_DRIVER),custom)
   SRC += $(ARM_ATSAM_DIR)/md_rgb_matrix.c
 endif
 SRC += $(ARM_ATSAM_DIR)/main_arm_atsam.c
-SRC += $(ARM_ATSAM_DIR)/spi.c
+SRC += $(ARM_ATSAM_DIR)/shift_register.c
+SRC += $(ARM_ATSAM_DIR)/spi_master.c
 SRC += $(ARM_ATSAM_DIR)/startup.c
 
 SRC += $(ARM_ATSAM_DIR)/usb/main_usb.c
diff --git a/tmk_core/protocol/arm_atsam/arm_atsam_protocol.h b/tmk_core/protocol/arm_atsam/arm_atsam_protocol.h
index d126c66e7..c3eab39fb 100644
--- a/tmk_core/protocol/arm_atsam/arm_atsam_protocol.h
+++ b/tmk_core/protocol/arm_atsam/arm_atsam_protocol.h
@@ -27,7 +27,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "wait.h"
 #include "adc.h"
 #include "i2c_master.h"
-#include "spi.h"
+#include "shift_register.h"
 
 #include "./usb/usb2422.h"
 
diff --git a/tmk_core/protocol/arm_atsam/shift_register.c b/tmk_core/protocol/arm_atsam/shift_register.c
new file mode 100644
index 000000000..8d63af1b5
--- /dev/null
+++ b/tmk_core/protocol/arm_atsam/shift_register.c
@@ -0,0 +1,118 @@
+/*
+Copyright 2018 Massdrop Inc.
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "arm_atsam_protocol.h"
+
+#include "spi_master.h"
+#include "wait.h"
+#include "gpio.h"
+
+// #define SR_USE_BITBANG
+
+// Bodge for when spi_master is not available
+#ifdef SR_USE_BITBANG
+#    define CLOCK_DELAY 10
+
+void shift_init_impl(void) {
+    setPinOutput(SR_EXP_RCLK_PIN);
+    setPinOutput(SPI_DATAOUT_PIN);
+    setPinOutput(SPI_SCLK_PIN);
+}
+
+void shift_out_impl(const uint8_t *data, uint16_t length) {
+    writePinLow(SR_EXP_RCLK_PIN);
+    for (uint16_t i = 0; i < length; i++) {
+        uint8_t val = data[i];
+
+        // shift out lsb first
+        for (uint8_t bit = 0; bit < 8; bit++) {
+            writePin(SPI_DATAOUT_PIN, !!(val & (1 << bit)));
+            writePin(SPI_SCLK_PIN, true);
+            wait_us(CLOCK_DELAY);
+
+            writePin(SPI_SCLK_PIN, false);
+            wait_us(CLOCK_DELAY);
+        }
+    }
+    writePinHigh(SR_EXP_RCLK_PIN);
+    return SPI_STATUS_SUCCESS;
+}
+
+#else
+
+void shift_init_impl(void) { spi_init(); }
+
+void shift_out_impl(const uint8_t *data, uint16_t length) {
+    spi_start(SR_EXP_RCLK_PIN, true, 0, 0);
+
+    spi_transmit(data, length);
+
+    spi_stop();
+}
+#endif
+
+// ***************************************************************
+
+void shift_out(const uint8_t *data, uint16_t length) { shift_out_impl(data, length); }
+
+void shift_enable(void) {
+    setPinOutput(SR_EXP_OE_PIN);
+    writePinLow(SR_EXP_OE_PIN);
+}
+
+void shift_disable(void) {
+    setPinOutput(SR_EXP_OE_PIN);
+    writePinHigh(SR_EXP_OE_PIN);
+}
+
+void shift_init(void) {
+    shift_disable();
+    shift_init_impl();
+}
+
+// ***************************************************************
+
+sr_exp_t sr_exp_data;
+
+void SR_EXP_WriteData(void) {
+    uint8_t data[2] = {
+        sr_exp_data.reg & 0xFF,         // Shift in bits 7-0
+        (sr_exp_data.reg >> 8) & 0xFF,  // Shift in bits 15-8
+    };
+    shift_out(data, 2);
+}
+
+void SR_EXP_Init(void) {
+    shift_init();
+
+    sr_exp_data.reg             = 0;
+    sr_exp_data.bit.HUB_CONNECT = 0;
+    sr_exp_data.bit.HUB_RESET_N = 0;
+    sr_exp_data.bit.S_UP        = 0;
+    sr_exp_data.bit.E_UP_N      = 1;
+    sr_exp_data.bit.S_DN1       = 1;
+    sr_exp_data.bit.E_DN1_N     = 1;
+    sr_exp_data.bit.E_VBUS_1    = 0;
+    sr_exp_data.bit.E_VBUS_2    = 0;
+    sr_exp_data.bit.SRC_1       = 1;
+    sr_exp_data.bit.SRC_2       = 1;
+    sr_exp_data.bit.IRST        = 1;
+    sr_exp_data.bit.SDB_N       = 0;
+    SR_EXP_WriteData();
+
+    shift_enable();
+}
diff --git a/tmk_core/protocol/arm_atsam/spi.h b/tmk_core/protocol/arm_atsam/shift_register.h
index dcd45f31a..56a8c7f71 100644
--- a/tmk_core/protocol/arm_atsam/spi.h
+++ b/tmk_core/protocol/arm_atsam/shift_register.h
@@ -15,28 +15,9 @@ You should have received a copy of the GNU General Public License
 along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#ifndef _SPI_H_
-#define _SPI_H_
+#pragma once
 
-/* Macros for Shift Register control */
-#define SR_EXP_RCLK_LO PORT->Group[SR_EXP_RCLK_PORT].OUTCLR.reg = (1 << SR_EXP_RCLK_PIN)
-#define SR_EXP_RCLK_HI PORT->Group[SR_EXP_RCLK_PORT].OUTSET.reg = (1 << SR_EXP_RCLK_PIN)
-#define SR_EXP_OE_N_ENA PORT->Group[SR_EXP_OE_N_PORT].OUTCLR.reg = (1 << SR_EXP_OE_N_PIN)
-#define SR_EXP_OE_N_DIS PORT->Group[SR_EXP_OE_N_PORT].OUTSET.reg = (1 << SR_EXP_OE_N_PIN)
-
-/* Determine bits to set for mux selection */
-#if SR_EXP_DATAOUT_PIN % 2 == 0
-#    define SR_EXP_DATAOUT_MUX_SEL PMUXE
-#else
-#    define SR_EXP_DATAOUT_MUX_SEL PMUXO
-#endif
-
-/* Determine bits to set for mux selection */
-#if SR_EXP_SCLK_PIN % 2 == 0
-#    define SR_EXP_SCLK_MUX_SEL PMUXE
-#else
-#    define SR_EXP_SCLK_MUX_SEL PMUXO
-#endif
+#include <stdint.h>
 
 /* Data structure to define Shift Register output expander hardware */
 /* This structure gets shifted into registers LSB first */
@@ -66,5 +47,3 @@ extern sr_exp_t sr_exp_data;
 
 void SR_EXP_WriteData(void);
 void SR_EXP_Init(void);
-
-#endif  //_SPI_H_
diff --git a/tmk_core/protocol/arm_atsam/spi.c b/tmk_core/protocol/arm_atsam/spi.c
deleted file mode 100644
index 3b118bc1f..000000000
--- a/tmk_core/protocol/arm_atsam/spi.c
+++ /dev/null
@@ -1,92 +0,0 @@
-/*
-Copyright 2018 Massdrop Inc.
-
-This program is free software: you can redistribute it and/or modify
-it under the terms of the GNU General Public License as published by
-the Free Software Foundation, either version 2 of the License, or
-(at your option) any later version.
-
-This program is distributed in the hope that it will be useful,
-but WITHOUT ANY WARRANTY; without even the implied warranty of
-MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-GNU General Public License for more details.
-
-You should have received a copy of the GNU General Public License
-along with this program.  If not, see <http://www.gnu.org/licenses/>.
-*/
-
-#include "arm_atsam_protocol.h"
-
-sr_exp_t sr_exp_data;
-
-void SR_EXP_WriteData(void) {
-    SR_EXP_RCLK_LO;
-
-    while (!(SR_EXP_SERCOM->SPI.INTFLAG.bit.DRE)) {
-        DBGC(DC_SPI_WRITE_DRE);
-    }
-
-    SR_EXP_SERCOM->SPI.DATA.bit.DATA = sr_exp_data.reg & 0xFF;  // Shift in bits 7-0
-    while (!(SR_EXP_SERCOM->SPI.INTFLAG.bit.TXC)) {
-        DBGC(DC_SPI_WRITE_TXC_1);
-    }
-
-    SR_EXP_SERCOM->SPI.DATA.bit.DATA = (sr_exp_data.reg >> 8) & 0xFF;  // Shift in bits 15-8
-    while (!(SR_EXP_SERCOM->SPI.INTFLAG.bit.TXC)) {
-        DBGC(DC_SPI_WRITE_TXC_2);
-    }
-
-    SR_EXP_RCLK_HI;
-}
-
-void SR_EXP_Init(void) {
-    DBGC(DC_SPI_INIT_BEGIN);
-
-    CLK_set_spi_freq(CHAN_SERCOM_SPI, FREQ_SPI_DEFAULT);
-
-    // Set up MCU Shift Register pins
-    PORT->Group[SR_EXP_RCLK_PORT].DIRSET.reg = (1 << SR_EXP_RCLK_PIN);
-    PORT->Group[SR_EXP_OE_N_PORT].DIRSET.reg = (1 << SR_EXP_OE_N_PIN);
-
-    // Set up MCU SPI pins
-    PORT->Group[SR_EXP_DATAOUT_PORT].PMUX[SR_EXP_DATAOUT_PIN / 2].bit.SR_EXP_DATAOUT_MUX_SEL = SR_EXP_DATAOUT_MUX;  // MUX select for sercom
-    PORT->Group[SR_EXP_SCLK_PORT].PMUX[SR_EXP_SCLK_PIN / 2].bit.SR_EXP_SCLK_MUX_SEL          = SR_EXP_SCLK_MUX;     // MUX select for sercom
-    PORT->Group[SR_EXP_DATAOUT_PORT].PINCFG[SR_EXP_DATAOUT_PIN].bit.PMUXEN                   = 1;                   // MUX Enable
-    PORT->Group[SR_EXP_SCLK_PORT].PINCFG[SR_EXP_SCLK_PIN].bit.PMUXEN                         = 1;                   // MUX Enable
-
-    // Initialize Shift Register
-    SR_EXP_OE_N_DIS;
-    SR_EXP_RCLK_HI;
-
-    SR_EXP_SERCOM->SPI.CTRLA.bit.DORD = 1;  // Data Order - LSB is transferred first
-    SR_EXP_SERCOM->SPI.CTRLA.bit.CPOL = 1;  // Clock Polarity - SCK high when idle. Leading edge of cycle is falling. Trailing rising.
-    SR_EXP_SERCOM->SPI.CTRLA.bit.CPHA = 1;  // Clock Phase - Leading Edge Falling, change, Trailing Edge - Rising, sample
-    SR_EXP_SERCOM->SPI.CTRLA.bit.DIPO = 3;  // Data In Pinout - SERCOM PAD[3] is used as data input (Configure away from DOPO. Not using input.)
-    SR_EXP_SERCOM->SPI.CTRLA.bit.DOPO = 0;  // Data Output PAD[0], Serial Clock PAD[1]
-    SR_EXP_SERCOM->SPI.CTRLA.bit.MODE = 3;  // Operating Mode - Master operation
-
-    SR_EXP_SERCOM->SPI.CTRLA.bit.ENABLE = 1;  // Enable - Peripheral is enabled or being enabled
-    while (SR_EXP_SERCOM->SPI.SYNCBUSY.bit.ENABLE) {
-        DBGC(DC_SPI_SYNC_ENABLING);
-    }
-
-    sr_exp_data.reg             = 0;
-    sr_exp_data.bit.HUB_CONNECT = 0;
-    sr_exp_data.bit.HUB_RESET_N = 0;
-    sr_exp_data.bit.S_UP        = 0;
-    sr_exp_data.bit.E_UP_N      = 1;
-    sr_exp_data.bit.S_DN1       = 1;
-    sr_exp_data.bit.E_DN1_N     = 1;
-    sr_exp_data.bit.E_VBUS_1    = 0;
-    sr_exp_data.bit.E_VBUS_2    = 0;
-    sr_exp_data.bit.SRC_1       = 1;
-    sr_exp_data.bit.SRC_2       = 1;
-    sr_exp_data.bit.IRST        = 1;
-    sr_exp_data.bit.SDB_N       = 0;
-    SR_EXP_WriteData();
-
-    // Enable Shift Register output
-    SR_EXP_OE_N_ENA;
-
-    DBGC(DC_SPI_INIT_COMPLETE);
-}
diff --git a/tmk_core/protocol/arm_atsam/spi_master.c b/tmk_core/protocol/arm_atsam/spi_master.c
new file mode 100644
index 000000000..9781d45b1
--- /dev/null
+++ b/tmk_core/protocol/arm_atsam/spi_master.c
@@ -0,0 +1,109 @@
+/*
+Copyright 2018 Massdrop Inc.
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "arm_atsam_protocol.h"
+#include "spi_master.h"
+#include "gpio.h"
+
+/* Determine bits to set for mux selection */
+#if SPI_DATAOUT_PIN % 2 == 0
+#    define SPI_DATAOUT_MUX_SEL PMUXE
+#else
+#    define SPI_DATAOUT_MUX_SEL PMUXO
+#endif
+
+/* Determine bits to set for mux selection */
+#if SPI_SCLK_PIN % 2 == 0
+#    define SPI_SCLK_MUX_SEL PMUXE
+#else
+#    define SPI_SCLK_MUX_SEL PMUXO
+#endif
+
+static pin_t currentSelectPin = NO_PIN;
+
+__attribute__((weak)) void spi_init(void) {
+    static bool is_initialised = false;
+    if (!is_initialised) {
+        is_initialised = true;
+
+        DBGC(DC_SPI_INIT_BEGIN);
+
+        CLK_set_spi_freq(CHAN_SERCOM_SPI, FREQ_SPI_DEFAULT);
+
+        // Set up MCU SPI pins
+        PORT->Group[SAMD_PORT(SPI_DATAOUT_PIN)].PMUX[SAMD_PIN(SPI_DATAOUT_PIN) / 2].bit.SPI_DATAOUT_MUX_SEL = SPI_DATAOUT_MUX;  // MUX select for sercom
+        PORT->Group[SAMD_PORT(SPI_SCLK_PIN)].PMUX[SAMD_PIN(SPI_SCLK_PIN) / 2].bit.SPI_SCLK_MUX_SEL          = SPI_SCLK_MUX;     // MUX select for sercom
+        PORT->Group[SAMD_PORT(SPI_DATAOUT_PIN)].PINCFG[SAMD_PIN(SPI_DATAOUT_PIN)].bit.PMUXEN                = 1;                // MUX Enable
+        PORT->Group[SAMD_PORT(SPI_SCLK_PIN)].PINCFG[SAMD_PIN(SPI_SCLK_PIN)].bit.PMUXEN                      = 1;                // MUX Enable
+
+        DBGC(DC_SPI_INIT_COMPLETE);
+    }
+}
+
+bool spi_start(pin_t csPin, bool lsbFirst, uint8_t mode, uint16_t divisor) {
+    if (currentSelectPin != NO_PIN || csPin == NO_PIN) {
+        return false;
+    }
+
+    currentSelectPin = csPin;
+    setPinOutput(currentSelectPin);
+    writePinLow(currentSelectPin);
+
+    SPI_SERCOM->SPI.CTRLA.bit.DORD = lsbFirst;  // Data Order - LSB is transferred first
+    SPI_SERCOM->SPI.CTRLA.bit.CPOL = 1;         // Clock Polarity - SCK high when idle. Leading edge of cycle is falling. Trailing rising.
+    SPI_SERCOM->SPI.CTRLA.bit.CPHA = 1;         // Clock Phase - Leading Edge Falling, change, Trailing Edge - Rising, sample
+    SPI_SERCOM->SPI.CTRLA.bit.DIPO = 3;         // Data In Pinout - SERCOM PAD[3] is used as data input (Configure away from DOPO. Not using input.)
+    SPI_SERCOM->SPI.CTRLA.bit.DOPO = 0;         // Data Output PAD[0], Serial Clock PAD[1]
+    SPI_SERCOM->SPI.CTRLA.bit.MODE = 3;         // Operating Mode - Master operation
+
+    SPI_SERCOM->SPI.CTRLA.bit.ENABLE = 1;  // Enable - Peripheral is enabled or being enabled
+    while (SPI_SERCOM->SPI.SYNCBUSY.bit.ENABLE) {
+        DBGC(DC_SPI_SYNC_ENABLING);
+    }
+    return true;
+}
+
+spi_status_t spi_transmit(const uint8_t *data, uint16_t length) {
+    while (!(SPI_SERCOM->SPI.INTFLAG.bit.DRE)) {
+        DBGC(DC_SPI_WRITE_DRE);
+    }
+
+    for (uint16_t i = 0; i < length; i++) {
+        SPI_SERCOM->SPI.DATA.bit.DATA = data[i];
+        while (!(SPI_SERCOM->SPI.INTFLAG.bit.TXC)) {
+            DBGC(DC_SPI_WRITE_TXC_1);
+        }
+    }
+
+    return SPI_STATUS_SUCCESS;
+}
+
+void spi_stop(void) {
+    if (currentSelectPin != NO_PIN) {
+        setPinOutput(currentSelectPin);
+        writePinHigh(currentSelectPin);
+        currentSelectPin = NO_PIN;
+    }
+}
+
+// Not implemented yet....
+
+spi_status_t spi_write(uint8_t data);
+
+spi_status_t spi_read(void);
+
+spi_status_t spi_receive(uint8_t *data, uint16_t length);
diff --git a/tmk_core/protocol/arm_atsam/spi_master.h b/tmk_core/protocol/arm_atsam/spi_master.h
new file mode 100644
index 000000000..26c55128b
--- /dev/null
+++ b/tmk_core/protocol/arm_atsam/spi_master.h
@@ -0,0 +1,48 @@
+/* Copyright 2021 QMK
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <stdbool.h>
+
+typedef int16_t spi_status_t;
+
+#define SPI_STATUS_SUCCESS (0)
+#define SPI_STATUS_ERROR (-1)
+#define SPI_STATUS_TIMEOUT (-2)
+
+#define SPI_TIMEOUT_IMMEDIATE (0)
+#define SPI_TIMEOUT_INFINITE (0xFFFF)
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+void spi_init(void);
+
+bool spi_start(pin_t slavePin, bool lsbFirst, uint8_t mode, uint16_t divisor);
+
+spi_status_t spi_write(uint8_t data);
+
+spi_status_t spi_read(void);
+
+spi_status_t spi_transmit(const uint8_t *data, uint16_t length);
+
+spi_status_t spi_receive(uint8_t *data, uint16_t length);
+
+void spi_stop(void);
+#ifdef __cplusplus
+}
+#endif