8 files changed, 686 insertions, 25 deletions

diff --git a/platforms/avr/drivers/analog.c b/platforms/avr/drivers/analog.c
index 8d299ffdb..628835cce 100644
--- a/platforms/avr/drivers/analog.c
+++ b/platforms/avr/drivers/analog.c
@@ -23,29 +23,6 @@ static uint8_t aref = ADC_REF_POWER;
 
 void analogReference(uint8_t mode) { aref = mode & (_BV(REFS1) | _BV(REFS0)); }
 
-// Arduino compatible pin input
-int16_t analogRead(uint8_t pin) {
-#if defined(__AVR_ATmega32U4__)
-    // clang-format off
-    static const uint8_t PROGMEM pin_to_mux[] = {
-        //A0    A1    A2    A3    A4    A5
-        //F7    F6    F5    F4    F1    F0
-        0x07, 0x06, 0x05, 0x04, 0x01, 0x00,
-        //A6    A7    A8    A9   A10   A11
-        //D4    D7    B4    B5    B6    D6
-        0x20, 0x22, 0x23, 0x24, 0x25, 0x21
-    };
-    // clang-format on
-    if (pin >= 12) return 0;
-    return adc_read(pgm_read_byte(pin_to_mux + pin));
-#elif defined(__AVR_AT90USB646__) || defined(__AVR_AT90USB647__) || defined(__AVR_AT90USB1286__) || defined(__AVR_AT90USB1287__) || defined(__AVR_ATmega328P__) || defined(__AVR_ATmega328__)
-    if (pin >= 8) return 0;
-    return adc_read(pin);
-#else
-    return 0;
-#endif
-}
-
 int16_t analogReadPin(pin_t pin) { return adc_read(pinToMux(pin)); }
 
 uint8_t pinToMux(pin_t pin) {
diff --git a/platforms/avr/drivers/analog.h b/platforms/avr/drivers/analog.h
index 058882450..fa2fb0d89 100644
--- a/platforms/avr/drivers/analog.h
+++ b/platforms/avr/drivers/analog.h
@@ -22,8 +22,7 @@
 #ifdef __cplusplus
 extern "C" {
 #endif
-void    analogReference(uint8_t mode);
-int16_t analogRead(uint8_t pin);
+void analogReference(uint8_t mode);
 
 int16_t analogReadPin(pin_t pin);
 uint8_t pinToMux(pin_t pin);
diff --git a/platforms/avr/drivers/audio_pwm.h b/platforms/avr/drivers/audio_pwm.h
new file mode 100644
index 000000000..d6eb3571d
--- /dev/null
+++ b/platforms/avr/drivers/audio_pwm.h
@@ -0,0 +1,17 @@
+/* Copyright 2020 Jack Humbert
+ * Copyright 2020 JohSchneider
+ *
+ * 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/>.
+ */
+#pragma once
diff --git a/platforms/avr/drivers/audio_pwm_hardware.c b/platforms/avr/drivers/audio_pwm_hardware.c
new file mode 100644
index 000000000..df03a4558
--- /dev/null
+++ b/platforms/avr/drivers/audio_pwm_hardware.c
@@ -0,0 +1,332 @@
+/* Copyright 2016 Jack Humbert
+ * Copyright 2020 JohSchneider
+ *
+ * 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/>.
+ */
+
+#if defined(__AVR__)
+#    include <avr/pgmspace.h>
+#    include <avr/interrupt.h>
+#    include <avr/io.h>
+#endif
+
+#include "audio.h"
+
+extern bool    playing_note;
+extern bool    playing_melody;
+extern uint8_t note_timbre;
+
+#define CPU_PRESCALER 8
+
+/*
+  Audio Driver: PWM
+
+  drive up to two speakers through the AVR PWM hardware-peripheral, using timer1 and/or timer3 on Atmega32U4.
+
+  the primary channel_1 can be connected to either pin PC4 PC5 or PC6 (the later being used by most AVR based keyboards) with a PMW signal generated by timer3
+  and an optional secondary channel_2 on either pin PB5, PB6 or PB7, with a PWM signal from timer1
+
+  alternatively, the PWM pins on PORTB can be used as only/primary speaker
+*/
+
+#if defined(AUDIO_PIN) && (AUDIO_PIN != C4) && (AUDIO_PIN != C5) && (AUDIO_PIN != C6) && (AUDIO_PIN != B5) && (AUDIO_PIN != B6) && (AUDIO_PIN != B7) && (AUDIO_PIN != D5)
+#    error "Audio feature enabled, but no suitable pin selected as AUDIO_PIN - see docs/feature_audio under the AVR settings for available options."
+#endif
+
+#if (AUDIO_PIN == C4) || (AUDIO_PIN == C5) || (AUDIO_PIN == C6)
+#    define AUDIO1_PIN_SET
+#    define AUDIO1_TIMSKx TIMSK3
+#    define AUDIO1_TCCRxA TCCR3A
+#    define AUDIO1_TCCRxB TCCR3B
+#    define AUDIO1_ICRx ICR3
+#    define AUDIO1_WGMx0 WGM30
+#    define AUDIO1_WGMx1 WGM31
+#    define AUDIO1_WGMx2 WGM32
+#    define AUDIO1_WGMx3 WGM33
+#    define AUDIO1_CSx0 CS30
+#    define AUDIO1_CSx1 CS31
+#    define AUDIO1_CSx2 CS32
+
+#    if (AUDIO_PIN == C6)
+#        define AUDIO1_COMxy0 COM3A0
+#        define AUDIO1_COMxy1 COM3A1
+#        define AUDIO1_OCIExy OCIE3A
+#        define AUDIO1_OCRxy OCR3A
+#        define AUDIO1_PIN C6
+#        define AUDIO1_TIMERx_COMPy_vect TIMER3_COMPA_vect
+#    elif (AUDIO_PIN == C5)
+#        define AUDIO1_COMxy0 COM3B0
+#        define AUDIO1_COMxy1 COM3B1
+#        define AUDIO1_OCIExy OCIE3B
+#        define AUDIO1_OCRxy OCR3B
+#        define AUDIO1_PIN C5
+#        define AUDIO1_TIMERx_COMPy_vect TIMER3_COMPB_vect
+#    elif (AUDIO_PIN == C4)
+#        define AUDIO1_COMxy0 COM3C0
+#        define AUDIO1_COMxy1 COM3C1
+#        define AUDIO1_OCIExy OCIE3C
+#        define AUDIO1_OCRxy OCR3C
+#        define AUDIO1_PIN C4
+#        define AUDIO1_TIMERx_COMPy_vect TIMER3_COMPC_vect
+#    endif
+#endif
+
+#if defined(AUDIO_PIN) && defined(AUDIO_PIN_ALT) && (AUDIO_PIN == AUDIO_PIN_ALT)
+#    error "Audio feature: AUDIO_PIN and AUDIO_PIN_ALT on the same pin makes no sense."
+#endif
+
+#if ((AUDIO_PIN == B5) && ((AUDIO_PIN_ALT == B6) || (AUDIO_PIN_ALT == B7))) || ((AUDIO_PIN == B6) && ((AUDIO_PIN_ALT == B5) || (AUDIO_PIN_ALT == B7))) || ((AUDIO_PIN == B7) && ((AUDIO_PIN_ALT == B5) || (AUDIO_PIN_ALT == B6)))
+#    error "Audio feature: PORTB as AUDIO_PIN and AUDIO_PIN_ALT at the same time is not supported."
+#endif
+
+#if defined(AUDIO_PIN_ALT) && (AUDIO_PIN_ALT != B5) && (AUDIO_PIN_ALT != B6) && (AUDIO_PIN_ALT != B7)
+#    error "Audio feature: the pin selected as AUDIO_PIN_ALT is not supported."
+#endif
+
+#if (AUDIO_PIN == B5) || (AUDIO_PIN == B6) || (AUDIO_PIN == B7) || (AUDIO_PIN_ALT == B5) || (AUDIO_PIN_ALT == B6) || (AUDIO_PIN_ALT == B7) || (AUDIO_PIN == D5)
+#    define AUDIO2_PIN_SET
+#    define AUDIO2_TIMSKx TIMSK1
+#    define AUDIO2_TCCRxA TCCR1A
+#    define AUDIO2_TCCRxB TCCR1B
+#    define AUDIO2_ICRx ICR1
+#    define AUDIO2_WGMx0 WGM10
+#    define AUDIO2_WGMx1 WGM11
+#    define AUDIO2_WGMx2 WGM12
+#    define AUDIO2_WGMx3 WGM13
+#    define AUDIO2_CSx0 CS10
+#    define AUDIO2_CSx1 CS11
+#    define AUDIO2_CSx2 CS12
+
+#    if (AUDIO_PIN == B5) || (AUDIO_PIN_ALT == B5)
+#        define AUDIO2_COMxy0 COM1A0
+#        define AUDIO2_COMxy1 COM1A1
+#        define AUDIO2_OCIExy OCIE1A
+#        define AUDIO2_OCRxy OCR1A
+#        define AUDIO2_PIN B5
+#        define AUDIO2_TIMERx_COMPy_vect TIMER1_COMPA_vect
+#    elif (AUDIO_PIN == B6) || (AUDIO_PIN_ALT == B6)
+#        define AUDIO2_COMxy0 COM1B0
+#        define AUDIO2_COMxy1 COM1B1
+#        define AUDIO2_OCIExy OCIE1B
+#        define AUDIO2_OCRxy OCR1B
+#        define AUDIO2_PIN B6
+#        define AUDIO2_TIMERx_COMPy_vect TIMER1_COMPB_vect
+#    elif (AUDIO_PIN == B7) || (AUDIO_PIN_ALT == B7)
+#        define AUDIO2_COMxy0 COM1C0
+#        define AUDIO2_COMxy1 COM1C1
+#        define AUDIO2_OCIExy OCIE1C
+#        define AUDIO2_OCRxy OCR1C
+#        define AUDIO2_PIN B7
+#        define AUDIO2_TIMERx_COMPy_vect TIMER1_COMPC_vect
+#    elif (AUDIO_PIN == D5) && defined(__AVR_ATmega32A__)
+#        pragma message "Audio support for ATmega32A is experimental and can cause crashes."
+#        undef AUDIO2_TIMSKx
+#        define AUDIO2_TIMSKx TIMSK
+#        define AUDIO2_COMxy0 COM1A0
+#        define AUDIO2_COMxy1 COM1A1
+#        define AUDIO2_OCIExy OCIE1A
+#        define AUDIO2_OCRxy OCR1A
+#        define AUDIO2_PIN D5
+#        define AUDIO2_TIMERx_COMPy_vect TIMER1_COMPA_vect
+#    endif
+#endif
+
+// C6 seems to be the assumed default by many existing keyboard - but sill warn the user
+#if !defined(AUDIO1_PIN_SET) && !defined(AUDIO2_PIN_SET)
+#    pragma message "Audio feature enabled, but no suitable pin selected - see docs/feature_audio under the AVR settings for available options. Don't expect to hear anything... :-)"
+// TODO: make this an error - go through the breaking-change-process and change all keyboards to the new define
+#endif
+// -----------------------------------------------------------------------------
+
+#ifdef AUDIO1_PIN_SET
+static float channel_1_frequency = 0.0f;
+void         channel_1_set_frequency(float freq) {
+    if (freq == 0.0f)  // a pause/rest is a valid "note" with freq=0
+    {
+        // disable the output, but keep the pwm-ISR going (with the previous
+        // frequency) so the audio-state keeps getting updated
+        // Note: setting the duty-cycle 0 is not possible on non-inverting PWM mode - see the AVR data-sheet
+        AUDIO1_TCCRxA &= ~(_BV(AUDIO1_COMxy1) | _BV(AUDIO1_COMxy0));
+        return;
+    } else {
+        AUDIO1_TCCRxA |= _BV(AUDIO1_COMxy1);  // enable output, PWM mode
+    }
+
+    channel_1_frequency = freq;
+
+    // set pwm period
+    AUDIO1_ICRx = (uint16_t)(((float)F_CPU) / (freq * CPU_PRESCALER));
+    // and duty cycle
+    AUDIO1_OCRxy = (uint16_t)((((float)F_CPU) / (freq * CPU_PRESCALER)) * note_timbre / 100);
+}
+
+void channel_1_start(void) {
+    // enable timer-counter ISR
+    AUDIO1_TIMSKx |= _BV(AUDIO1_OCIExy);
+    // enable timer-counter output
+    AUDIO1_TCCRxA |= _BV(AUDIO1_COMxy1);
+}
+
+void channel_1_stop(void) {
+    // disable timer-counter ISR
+    AUDIO1_TIMSKx &= ~_BV(AUDIO1_OCIExy);
+    // disable timer-counter output
+    AUDIO1_TCCRxA &= ~(_BV(AUDIO1_COMxy1) | _BV(AUDIO1_COMxy0));
+}
+#endif
+
+#ifdef AUDIO2_PIN_SET
+static float channel_2_frequency = 0.0f;
+void         channel_2_set_frequency(float freq) {
+    if (freq == 0.0f) {
+        AUDIO2_TCCRxA &= ~(_BV(AUDIO2_COMxy1) | _BV(AUDIO2_COMxy0));
+        return;
+    } else {
+        AUDIO2_TCCRxA |= _BV(AUDIO2_COMxy1);
+    }
+
+    channel_2_frequency = freq;
+
+    AUDIO2_ICRx  = (uint16_t)(((float)F_CPU) / (freq * CPU_PRESCALER));
+    AUDIO2_OCRxy = (uint16_t)((((float)F_CPU) / (freq * CPU_PRESCALER)) * note_timbre / 100);
+}
+
+float channel_2_get_frequency(void) { return channel_2_frequency; }
+
+void channel_2_start(void) {
+    AUDIO2_TIMSKx |= _BV(AUDIO2_OCIExy);
+    AUDIO2_TCCRxA |= _BV(AUDIO2_COMxy1);
+}
+
+void channel_2_stop(void) {
+    AUDIO2_TIMSKx &= ~_BV(AUDIO2_OCIExy);
+    AUDIO2_TCCRxA &= ~(_BV(AUDIO2_COMxy1) | _BV(AUDIO2_COMxy0));
+}
+#endif
+
+void audio_driver_initialize() {
+#ifdef AUDIO1_PIN_SET
+    channel_1_stop();
+    setPinOutput(AUDIO1_PIN);
+#endif
+
+#ifdef AUDIO2_PIN_SET
+    channel_2_stop();
+    setPinOutput(AUDIO2_PIN);
+#endif
+
+    // TCCR3A / TCCR3B: Timer/Counter #3 Control Registers TCCR3A/TCCR3B, TCCR1A/TCCR1B
+    // Compare Output Mode (COM3An and COM1An) = 0b00 = Normal port operation
+    //   OC3A -- PC6
+    //   OC3B -- PC5
+    //   OC3C -- PC4
+    //   OC1A -- PB5
+    //   OC1B -- PB6
+    //   OC1C -- PB7
+
+    // Waveform Generation Mode (WGM3n) = 0b1110 = Fast PWM Mode 14. Period = ICR3, Duty Cycle OCR3A)
+    //   OCR3A - PC6
+    //   OCR3B - PC5
+    //   OCR3C - PC4
+    //   OCR1A - PB5
+    //   OCR1B - PB6
+    //   OCR1C - PB7
+
+    // Clock Select (CS3n) = 0b010 = Clock / 8
+#ifdef AUDIO1_PIN_SET
+    // initialize timer-counter
+    AUDIO1_TCCRxA = (0 << AUDIO1_COMxy1) | (0 << AUDIO1_COMxy0) | (1 << AUDIO1_WGMx1) | (0 << AUDIO1_WGMx0);
+    AUDIO1_TCCRxB = (1 << AUDIO1_WGMx3) | (1 << AUDIO1_WGMx2) | (0 << AUDIO1_CSx2) | (1 << AUDIO1_CSx1) | (0 << AUDIO1_CSx0);
+#endif
+
+#ifdef AUDIO2_PIN_SET
+    AUDIO2_TCCRxA = (0 << AUDIO2_COMxy1) | (0 << AUDIO2_COMxy0) | (1 << AUDIO2_WGMx1) | (0 << AUDIO2_WGMx0);
+    AUDIO2_TCCRxB = (1 << AUDIO2_WGMx3) | (1 << AUDIO2_WGMx2) | (0 << AUDIO2_CSx2) | (1 << AUDIO2_CSx1) | (0 << AUDIO2_CSx0);
+#endif
+}
+
+void audio_driver_stop() {
+#ifdef AUDIO1_PIN_SET
+    channel_1_stop();
+#endif
+
+#ifdef AUDIO2_PIN_SET
+    channel_2_stop();
+#endif
+}
+
+void audio_driver_start(void) {
+#ifdef AUDIO1_PIN_SET
+    channel_1_start();
+    if (playing_note) {
+        channel_1_set_frequency(audio_get_processed_frequency(0));
+    }
+#endif
+
+#if !defined(AUDIO1_PIN_SET) && defined(AUDIO2_PIN_SET)
+    channel_2_start();
+    if (playing_note) {
+        channel_2_set_frequency(audio_get_processed_frequency(0));
+    }
+#endif
+}
+
+static volatile uint32_t isr_counter = 0;
+#ifdef AUDIO1_PIN_SET
+ISR(AUDIO1_TIMERx_COMPy_vect) {
+    isr_counter++;
+    if (isr_counter < channel_1_frequency / (CPU_PRESCALER * 8)) return;
+
+    isr_counter        = 0;
+    bool state_changed = audio_update_state();
+
+    if (!playing_note && !playing_melody) {
+        channel_1_stop();
+#    ifdef AUDIO2_PIN_SET
+        channel_2_stop();
+#    endif
+        return;
+    }
+
+    if (state_changed) {
+        channel_1_set_frequency(audio_get_processed_frequency(0));
+#    ifdef AUDIO2_PIN_SET
+        if (audio_get_number_of_active_tones() > 1) {
+            channel_2_set_frequency(audio_get_processed_frequency(1));
+        } else {
+            channel_2_stop();
+        }
+#    endif
+    }
+}
+#endif
+
+#if !defined(AUDIO1_PIN_SET) && defined(AUDIO2_PIN_SET)
+ISR(AUDIO2_TIMERx_COMPy_vect) {
+    isr_counter++;
+    if (isr_counter < channel_2_frequency / (CPU_PRESCALER * 8)) return;
+
+    isr_counter        = 0;
+    bool state_changed = audio_update_state();
+
+    if (!playing_note && !playing_melody) {
+        channel_2_stop();
+        return;
+    }
+
+    if (state_changed) {
+        channel_2_set_frequency(audio_get_processed_frequency(0));
+    }
+}
+#endif
diff --git a/platforms/avr/drivers/i2c_master.c b/platforms/avr/drivers/i2c_master.c
index 2773e0077..111b55d6b 100644
--- a/platforms/avr/drivers/i2c_master.c
+++ b/platforms/avr/drivers/i2c_master.c
@@ -202,6 +202,25 @@ i2c_status_t i2c_writeReg(uint8_t devaddr, uint8_t regaddr, const uint8_t* data,
     return status;
 }
 
+i2c_status_t i2c_writeReg16(uint8_t devaddr, uint16_t regaddr, const uint8_t* data, uint16_t length, uint16_t timeout) {
+    i2c_status_t status = i2c_start(devaddr | 0x00, timeout);
+    if (status >= 0) {
+        status = i2c_write(regaddr >> 8, timeout);
+
+        if (status >= 0) {
+            status = i2c_write(regaddr & 0xFF, timeout);
+
+            for (uint16_t i = 0; i < length && status >= 0; i++) {
+                status = i2c_write(data[i], timeout);
+            }
+        }
+    }
+
+    i2c_stop();
+
+    return status;
+}
+
 i2c_status_t i2c_readReg(uint8_t devaddr, uint8_t regaddr, uint8_t* data, uint16_t length, uint16_t timeout) {
     i2c_status_t status = i2c_start(devaddr, timeout);
     if (status < 0) {
@@ -235,6 +254,43 @@ error:
     return (status < 0) ? status : I2C_STATUS_SUCCESS;
 }
 
+i2c_status_t i2c_readReg16(uint8_t devaddr, uint16_t regaddr, uint8_t* data, uint16_t length, uint16_t timeout) {
+    i2c_status_t status = i2c_start(devaddr, timeout);
+    if (status < 0) {
+        goto error;
+    }
+
+    status = i2c_write(regaddr >> 8, timeout);
+    if (status < 0) {
+        goto error;
+    }
+    status = i2c_write(regaddr & 0xFF, timeout);
+    if (status < 0) {
+        goto error;
+    }
+
+    status = i2c_start(devaddr | 0x01, timeout);
+
+    for (uint16_t i = 0; i < (length - 1) && status >= 0; i++) {
+        status = i2c_read_ack(timeout);
+        if (status >= 0) {
+            data[i] = status;
+        }
+    }
+
+    if (status >= 0) {
+        status = i2c_read_nack(timeout);
+        if (status >= 0) {
+            data[(length - 1)] = status;
+        }
+    }
+
+error:
+    i2c_stop();
+
+    return (status < 0) ? status : I2C_STATUS_SUCCESS;
+}
+
 void i2c_stop(void) {
     // transmit STOP condition
     TWCR = (1 << TWINT) | (1 << TWEN) | (1 << TWSTO);
diff --git a/platforms/avr/drivers/i2c_master.h b/platforms/avr/drivers/i2c_master.h
index e5af73364..2d95846db 100644
--- a/platforms/avr/drivers/i2c_master.h
+++ b/platforms/avr/drivers/i2c_master.h
@@ -39,5 +39,7 @@ int16_t      i2c_read_nack(uint16_t timeout);
 i2c_status_t i2c_transmit(uint8_t address, const uint8_t* data, uint16_t length, uint16_t timeout);
 i2c_status_t i2c_receive(uint8_t address, uint8_t* data, uint16_t length, uint16_t timeout);
 i2c_status_t i2c_writeReg(uint8_t devaddr, uint8_t regaddr, const uint8_t* data, uint16_t length, uint16_t timeout);
+i2c_status_t i2c_writeReg16(uint8_t devaddr, uint16_t regaddr, const uint8_t* data, uint16_t length, uint16_t timeout);
 i2c_status_t i2c_readReg(uint8_t devaddr, uint8_t regaddr, uint8_t* data, uint16_t length, uint16_t timeout);
+i2c_status_t i2c_readReg16(uint8_t devaddr, uint16_t regaddr, uint8_t* data, uint16_t length, uint16_t timeout);
 void         i2c_stop(void);
diff --git a/platforms/avr/drivers/ps2/ps2_io.c b/platforms/avr/drivers/ps2/ps2_io.c
new file mode 100644
index 000000000..7c826fbf1
--- /dev/null
+++ b/platforms/avr/drivers/ps2/ps2_io.c
@@ -0,0 +1,51 @@
+#include <stdbool.h>
+#include "ps2_io.h"
+#include "gpio.h"
+#include "wait.h"
+
+/* Check port settings for clock and data line */
+#if !(defined(PS2_CLOCK_PIN))
+#    error "PS/2 clock setting is required in config.h"
+#endif
+
+#if !(defined(PS2_DATA_PIN))
+#    error "PS/2 data setting is required in config.h"
+#endif
+
+/*
+ * Clock
+ */
+void clock_init(void) {}
+
+void clock_lo(void) {
+    // Transition from input with pull-up to output low via Hi-Z instead of output high
+    writePinLow(PS2_CLOCK_PIN);
+    setPinOutput(PS2_CLOCK_PIN);
+}
+
+void clock_hi(void) { setPinInputHigh(PS2_CLOCK_PIN); }
+
+bool clock_in(void) {
+    setPinInputHigh(PS2_CLOCK_PIN);
+    wait_us(1);
+    return readPin(PS2_CLOCK_PIN);
+}
+
+/*
+ * Data
+ */
+void data_init(void) {}
+
+void data_lo(void) {
+    // Transition from input with pull-up to output low via Hi-Z instead of output high
+    writePinLow(PS2_DATA_PIN);
+    setPinOutput(PS2_DATA_PIN);
+}
+
+void data_hi(void) { setPinInputHigh(PS2_DATA_PIN); }
+
+bool data_in(void) {
+    setPinInputHigh(PS2_DATA_PIN);
+    wait_us(1);
+    return readPin(PS2_DATA_PIN);
+}
diff --git a/platforms/avr/drivers/ps2/ps2_usart.c b/platforms/avr/drivers/ps2/ps2_usart.c
new file mode 100644
index 000000000..151cfcd68
--- /dev/null
+++ b/platforms/avr/drivers/ps2/ps2_usart.c
@@ -0,0 +1,227 @@
+/*
+Copyright 2010,2011,2012,2013 Jun WAKO <wakojun@gmail.com>
+
+This software is licensed with a Modified BSD License.
+All of this is supposed to be Free Software, Open Source, DFSG-free,
+GPL-compatible, and OK to use in both free and proprietary applications.
+Additions and corrections to this file are welcome.
+
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+* Redistributions of source code must retain the above copyright
+  notice, this list of conditions and the following disclaimer.
+
+* Redistributions in binary form must reproduce the above copyright
+  notice, this list of conditions and the following disclaimer in
+  the documentation and/or other materials provided with the
+  distribution.
+
+* Neither the name of the copyright holders nor the names of
+  contributors may be used to endorse or promote products derived
+  from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
+*/
+
+/*
+ * PS/2 protocol USART version
+ */
+
+#include <stdbool.h>
+#include <avr/interrupt.h>
+#include <util/delay.h>
+#include "gpio.h"
+#include "ps2.h"
+#include "ps2_io.h"
+#include "print.h"
+
+#ifndef PS2_CLOCK_DDR
+#    define PS2_CLOCK_DDR PORTx_ADDRESS(PS2_CLOCK_PIN)
+#endif
+#ifndef PS2_CLOCK_BIT
+#    define PS2_CLOCK_BIT (PS2_CLOCK_PIN & 0xF)
+#endif
+#ifndef PS2_DATA_DDR
+#    define PS2_DATA_DDR PORTx_ADDRESS(PS2_DATA_PIN)
+#endif
+#ifndef PS2_DATA_BIT
+#    define PS2_DATA_BIT (PS2_DATA_PIN & 0xF)
+#endif
+
+#define WAIT(stat, us, err)     \
+    do {                        \
+        if (!wait_##stat(us)) { \
+            ps2_error = err;    \
+            goto ERROR;         \
+        }                       \
+    } while (0)
+
+uint8_t ps2_error = PS2_ERR_NONE;
+
+static inline uint8_t pbuf_dequeue(void);
+static inline void    pbuf_enqueue(uint8_t data);
+static inline bool    pbuf_has_data(void);
+static inline void    pbuf_clear(void);
+
+void ps2_host_init(void) {
+    idle();  // without this many USART errors occur when cable is disconnected
+    PS2_USART_INIT();
+    PS2_USART_RX_INT_ON();
+    // POR(150-2000ms) plus BAT(300-500ms) may take 2.5sec([3]p.20)
+    //_delay_ms(2500);
+}
+
+uint8_t ps2_host_send(uint8_t data) {
+    bool parity = true;
+    ps2_error   = PS2_ERR_NONE;
+
+    PS2_USART_OFF();
+
+    /* terminate a transmission if we have */
+    inhibit();
+    _delay_us(100);  // [4]p.13
+
+    /* 'Request to Send' and Start bit */
+    data_lo();
+    clock_hi();
+    WAIT(clock_lo, 10000, 10);  // 10ms [5]p.50
+
+    /* Data bit[2-9] */
+    for (uint8_t i = 0; i < 8; i++) {
+        _delay_us(15);
+        if (data & (1 << i)) {
+            parity = !parity;
+            data_hi();
+        } else {
+            data_lo();
+        }
+        WAIT(clock_hi, 50, 2);
+        WAIT(clock_lo, 50, 3);
+    }
+
+    /* Parity bit */
+    _delay_us(15);
+    if (parity) {
+        data_hi();
+    } else {
+        data_lo();
+    }
+    WAIT(clock_hi, 50, 4);
+    WAIT(clock_lo, 50, 5);
+
+    /* Stop bit */
+    _delay_us(15);
+    data_hi();
+
+    /* Ack */
+    WAIT(data_lo, 50, 6);
+    WAIT(clock_lo, 50, 7);
+
+    /* wait for idle state */
+    WAIT(clock_hi, 50, 8);
+    WAIT(data_hi, 50, 9);
+
+    idle();
+    PS2_USART_INIT();
+    PS2_USART_RX_INT_ON();
+    return ps2_host_recv_response();
+ERROR:
+    idle();
+    PS2_USART_INIT();
+    PS2_USART_RX_INT_ON();
+    return 0;
+}
+
+uint8_t ps2_host_recv_response(void) {
+    // Command may take 25ms/20ms at most([5]p.46, [3]p.21)
+    uint8_t retry = 25;
+    while (retry-- && !pbuf_has_data()) {
+        _delay_ms(1);
+    }
+    return pbuf_dequeue();
+}
+
+uint8_t ps2_host_recv(void) {
+    if (pbuf_has_data()) {
+        ps2_error = PS2_ERR_NONE;
+        return pbuf_dequeue();
+    } else {
+        ps2_error = PS2_ERR_NODATA;
+        return 0;
+    }
+}
+
+ISR(PS2_USART_RX_VECT) {
+    // TODO: request RESEND when error occurs?
+    uint8_t error = PS2_USART_ERROR;  // USART error should be read before data
+    uint8_t data  = PS2_USART_RX_DATA;
+    if (!error) {
+        pbuf_enqueue(data);
+    } else {
+        xprintf("PS2 USART error: %02X data: %02X\n", error, data);
+    }
+}
+
+/* send LED state to keyboard */
+void ps2_host_set_led(uint8_t led) {
+    ps2_host_send(0xED);
+    ps2_host_send(led);
+}
+
+/*--------------------------------------------------------------------
+ * Ring buffer to store scan codes from keyboard
+ *------------------------------------------------------------------*/
+#define PBUF_SIZE 32
+static uint8_t     pbuf[PBUF_SIZE];
+static uint8_t     pbuf_head = 0;
+static uint8_t     pbuf_tail = 0;
+static inline void pbuf_enqueue(uint8_t data) {
+    uint8_t sreg = SREG;
+    cli();
+    uint8_t next = (pbuf_head + 1) % PBUF_SIZE;
+    if (next != pbuf_tail) {
+        pbuf[pbuf_head] = data;
+        pbuf_head       = next;
+    } else {
+        print("pbuf: full\n");
+    }
+    SREG = sreg;
+}
+static inline uint8_t pbuf_dequeue(void) {
+    uint8_t val = 0;
+
+    uint8_t sreg = SREG;
+    cli();
+    if (pbuf_head != pbuf_tail) {
+        val       = pbuf[pbuf_tail];
+        pbuf_tail = (pbuf_tail + 1) % PBUF_SIZE;
+    }
+    SREG = sreg;
+
+    return val;
+}
+static inline bool pbuf_has_data(void) {
+    uint8_t sreg = SREG;
+    cli();
+    bool has_data = (pbuf_head != pbuf_tail);
+    SREG          = sreg;
+    return has_data;
+}
+static inline void pbuf_clear(void) {
+    uint8_t sreg = SREG;
+    cli();
+    pbuf_head = pbuf_tail = 0;
+    SREG                  = sreg;
+}