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+### GNU GENERAL PUBLIC LICENSE
+
+Version 3, 29 June 2007
+
+Copyright (C) 2007 Free Software Foundation, Inc.
+<https://fsf.org/>
+
+Everyone is permitted to copy and distribute verbatim copies of this
+license document, but changing it is not allowed.
+
+### Preamble
+
+The GNU General Public License is a free, copyleft license for
+software and other kinds of works.
+
+The licenses for most software and other practical works are designed
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+free software for all its users. We, the Free Software Foundation, use
+the GNU General Public License for most of our software; it applies
+also to any other work released this way by its authors. You can apply
+it to your programs, too.
+
+When we speak of free software, we are referring to freedom, not
+price. Our General Public Licenses are designed to make sure that you
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+Developers that use the GNU GPL protect your rights with two steps:
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+The precise terms and conditions for copying, distribution and
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+
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+
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+
+#### 12. No Surrender of Others' Freedom.
+
+If conditions are imposed on you (whether by court order, agreement or
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+
+#### 13. Use with the GNU Affero General Public License.
+
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+
+#### 14. Revised Versions of this License.
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+
+#### 15. Disclaimer of Warranty.
+
+THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
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+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT
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+
+#### 16. Limitation of Liability.
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+PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
+
+#### 17. Interpretation of Sections 15 and 16.
+
+If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+END OF TERMS AND CONDITIONS
+
+### How to Apply These Terms to Your New Programs
+
+If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these
+terms.
+
+To do so, attach the following notices to the program. It is safest to
+attach them to the start of each source file to most effectively state
+the exclusion of warranty; and each file should have at least the
+"copyright" line and a pointer to where the full notice is found.
+
+        <one line to give the program's name and a brief idea of what it does.>
+        Copyright (C) <year>  <name of author>
+
+        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/>.
+
+Also add information on how to contact you by electronic and paper
+mail.
+
+If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+        <program>  Copyright (C) <year>  <name of author>
+        This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+        This is free software, and you are welcome to redistribute it
+        under certain conditions; type `show c' for details.
+
+The hypothetical commands \`show w' and \`show c' should show the
+appropriate parts of the General Public License. Of course, your
+program's commands might be different; for a GUI interface, you would
+use an "about box".
+
+You should also get your employer (if you work as a programmer) or
+school, if any, to sign a "copyright disclaimer" for the program, if
+necessary. For more information on this, and how to apply and follow
+the GNU GPL, see <https://www.gnu.org/licenses/>.
+
+The GNU General Public License does not permit incorporating your
+program into proprietary programs. If your program is a subroutine
+library, you may consider it more useful to permit linking proprietary
+applications with the library. If this is what you want to do, use the
+GNU Lesser General Public License instead of this License. But first,
+please read <https://www.gnu.org/licenses/why-not-lgpl.html>.

Makefile

@@ -0,0 +1,127 @@
+MCU=attiny13
+# MCU=attiny24A # this is for tests of >1kB firmware
+CC=avr-gcc -mmcu=$(MCU) -I$(INCLUDE_DIRS) -Os -fshort-enums
+INCLUDE_DIRS=autoinclude
+MAKEHEX=avr-objcopy -O ihex
+AVRDUDE=avrdude
+
+# Make sure the programmer port is correct for you! For security reasons, we do
+# not script automatic port detection here. Please find the correct port
+# manually and change the variable PROGRAMMER_TTY here accordingly.
+ifeq ($(OS),Windows_NT)
+    # Use the command `mode` to find the COM port on Windows.
+    PROGRAMMER_TTY=COM3
+else
+    # Use the command `ls /dev/ttyUSB*` to find the port on Linux. Please make sure
+    # the correct /dev/ttyUSBx has write permissions for everyone (at least 0666).
+    # If for some reason you cannot change those, change the line
+    # 	AVRDUDE=avrdude 
+    # above to 
+    # 	AVRDUDE=sudo avrdude
+    # and program the chip with sudo permissions.
+    PROGRAMMER_TTY=/dev/ttyUSB0
+endif
+
+# Make sure this is your programmer board. We assume STK500 as the default.
+PROGRAMMER_BOARD=avrisp
+# Only stk500 and avrisp (Arduino ISP) have been tested, so you will have to
+# set the PROGRAMMER_BAUDRATE variable manually if you use any other
+# programmer.
+
+ifeq ($(PROGRAMMER_BOARD),stk500)
+    PROGRAMMER_BAUDRATE=115200
+endif
+ifeq ($(PROGRAMMER_BOARD),avrisp)
+    # Arduino ISP - a DIY programmer made from Arduino, see
+    # https://docs.arduino.cc/built-in-examples/arduino-isp/ArduinoISP
+    PROGRAMMER_BAUDRATE=19200
+endif
+
+all: build/main.hex
+
+
+build:
+	mkdir -p build
+
+burn:
+	mkdir -p burn
+
+autoinclude:
+	mkdir -p autoinclude
+
+autoinclude/tinyqirx_conf.auto.h: conf/tinyqirx.conf autoinclude bin/generate_precalculation_header.py
+	python bin/generate_precalculation_header.py $< $@
+
+build/main.hex: build/main.o
+	avr-size --mcu=$(MCU) build/main.o
+	$(MAKEHEX) $< $@
+
+build/main.cc: src/main.c src/tinyqirx_core.c src/tinyqirx.c src/tinyqirx_utils.c autoinclude/tinyqirx_conf.auto.h
+	$(CC) -E $< -o $@
+
+build/main.S: src/main.c src/tinyqirx_core.c src/tinyqirx.c src/tinyqirx_utils.c autoinclude/tinyqirx_conf.auto.h
+	$(CC) -S $< -o $@
+
+build/main.o: src/main.c build src/tinyqirx_core.c src/tinyqirx.c src/tinyqirx_utils.c autoinclude/tinyqirx_conf.auto.h
+	$(CC) $< -o $@
+
+.PHONY: install clean asm readfuses
+
+# For some reason, this command is prone to yielding "Unexpected Device
+# signature, 0x0000" and "Verification error, first mismatch at byte 0x0000"
+# errors.  Just run it multiple times until succeeded. If it does not, try
+# moving the wires.
+install: build/main.hex
+	$(AVRDUDE) -c $(PROGRAMMER_BOARD) -p $(MCU) -P $(PROGRAMMER_TTY) -b $(PROGRAMMER_BAUDRATE) -U flash:w:$<:i -F
+
+
+
+burn/ensure_write.txt: burn
+	touch burn/ensure_write.txt
+
+writefuses: burn/writehfuse.hex burn/writelfuse.hex
+#	$(AVRDUDE) -c $(PROGRAMMER_BOARD) -p $(MCU) -P $(PROGRAMMER_TTY) -b $(PROGRAMMER_BAUDRATE) -U hfuse:w:burn/writehfuse.hex:i -F
+	$(AVRDUDE) -c $(PROGRAMMER_BOARD) -p $(MCU) -P $(PROGRAMMER_TTY) -b $(PROGRAMMER_BAUDRATE) -U lfuse:w:burn/writelfuse.hex:i -F
+
+burn/writehfuse.hex: burn/writehfuse.bin
+	avr-objcopy -O ihex -I binary $< $@
+
+burn/writelfuse.hex: burn/writelfuse.bin
+	avr-objcopy -O ihex -I binary $< $@
+
+burn/writehfuse.bin: setfuse/hfuse.txt
+	xxd -ps -r $< > $@
+
+burn/writelfuse.bin: setfuse/lfuse.txt
+	xxd -ps -r $< > $@
+
+burn/ensure_read.txt: burn
+	touch burn/ensure_read.txt
+
+burn/readhfuse.hex: burn/ensure_read.txt
+	$(AVRDUDE) -c $(PROGRAMMER_BOARD) -p $(MCU) -P $(PROGRAMMER_TTY) -b $(PROGRAMMER_BAUDRATE) -U hfuse:r:$@:i -F
+
+burn/readlfuse.hex: burn/ensure_read.txt
+	$(AVRDUDE) -c $(PROGRAMMER_BOARD) -p $(MCU) -P $(PROGRAMMER_TTY) -b $(PROGRAMMER_BAUDRATE) -U lfuse:r:$@:i -F
+
+burn/readhfuse.bin: burn/readhfuse.hex
+	avr-objcopy -I ihex -O binary $< $@
+
+burn/readlfuse.bin: burn/readlfuse.hex
+	avr-objcopy -I ihex -O binary $< $@
+
+burn/readhfuse.txt: burn/readhfuse.bin
+	xxd -ps $< > $@
+
+burn/readlfuse.txt: burn/readlfuse.bin
+	xxd -ps $< > $@
+
+readfuses: burn/readhfuse.txt burn/readlfuse.txt
+	cat burn/readhfuse.txt burn/readlfuse.txt
+	rm burn/ensure_read.txt
+
+clean:
+	rm -rf build autoinclude burn
+
+asm: build/main.S build/main.cc
+#asm: build/main.cc

README.md

@@ -0,0 +1,3 @@
+# TinyQiRx
+
+Qi protocol receiver implementation for tiny microcontrollers.

conf/tinyqirx.conf

@@ -0,0 +1,72 @@
+[tinyqirx]
+
+# Manufacturer code, 16-bit integer in hex
+ManufacturerCode = 0x0010
+
+# Qi receiver device unique identifier, must be a 32-bit integer in hex from
+# 0x00000000 to 0x7FFFFFFF
+DeviceIdentifier = 0x001b2529
+
+# Preamble length (must be at least 5.5 ms, but not longer than 12.5 ms)
+PreambleLength = 11 [ms]
+
+# Pause between packets (must be at least 6 ms, but not longer than
+# [22 ms - PreambleLength])
+SilentWindow = 7 [ms]
+
+# Power measurement window size (must be a multiple of 4 ms and at least 8 ms)
+WindowSize = 8 [ms]
+
+# Power measurement window offset (must be a multiple of 4 ms and at least as
+# long as the preamble length)
+WindowOffset = 12 [ms]
+
+# The target voltage on the rectifier
+SetpointVoltage = 7.5 [V]
+
+# Allowed variation of the target voltage on the rectifier
+SetpointVoltageTolerance = 1.0 [V]
+
+# Maximum expected voltage on the rectifier output. Exceeding this value will
+# shut down the receiver.
+MaximumExpectedVoltage = 12 [V]
+
+# Maximum expected current. Exceeding this value will shut down the receiver.
+MaximumExpectedCurrent = 1000 [mA]
+
+# Portion of current flowing through the current-measuring resistor, per a bit
+# returned by the function which performs the measurement of this current
+CurrentPerBit = 10.7422 [mA]
+
+# Portion of the voltage on the rectifier, per a bit returned by the function
+# which performs the measurement of this voltage
+VoltagePerBit = 47.266 [mV]
+
+# Reference power, must be from 0.5 to 5.0 W. This is roughly the maximum
+# expected received power.
+ReferencePower = 5.0 [W]
+
+# Power overestimation factor
+PowerOverestimationFactor = 1.5
+
+# Whether cutoff current should be used
+UseCutoffCurrent = no
+
+# Cutoff current
+CutoffCurrent = 1 [mA]
+
+# Whether the current setup facilitates battery temperature measurement
+UseTemperatureControl = no
+
+# Whether precise division should be used in calculation. Most cheap
+# microcontrollers do not implement division in hardware, so enabling this will
+# lead to inclusion of code implementing software division. This may increase
+# the firmware size severely. If left disabled approximate software division by
+# a constant will be used instead, which has a 1% error but takes only a few
+# processor instructions. This approximate division works as follows. First,
+# (2^24 / divisor) is precalculated before compilation. This is multiplied by
+# the dividend in runtime, all in 32-bit values. Finally, the result is
+# right-shifted by 16 bits, resulting in (256 * dividend / divisor) with 1%
+# accuracy.
+# 256 * dividend / divisor =~= [(2^24 / divisor) * dividend] / 2^16.
+UsePreciseDivision = no

setfuse/hfuse.txt

@@ -0,0 +1 @@
+fd

setfuse/lfuse.txt

@@ -0,0 +1,2 @@
+62
+

src/main.c

@@ -0,0 +1,120 @@
+// Verified to compile correctly with avr-gcc 5.4.0
+
+// The device must run at factory fuses: 9.6 MHz frequency with CKDIV8 enabled,
+// therefore the CPU clock must run at 1.2 MHz.
+//
+// We reprogram the fuses to use the 128 kHz clock without CKDIV8.
+//#define F_CPU 128000UL // this line must be before #include <util/delay.h>!
+#define F_CPU 1200000UL // this line must be before #include <util/delay.h>!
+
+// We assume 20% accuracy of the CPU frequency, so the Timer/Counter accuracy
+// is also assumed to be equal to 20%.
+#define F_CPU_ACCURACY_PERCENT 20
+
+#include <avr/interrupt.h>
+#include <util/delay.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+
+// ADC multiplexer constants, as defined by the ATTiny13A docs (ADMUX
+// register), to select the ADC listening pin
+#define ADC_ON_PB2 1
+#define ADC_ON_PB3 3
+#define ADC_ON_PB4 2
+#define ADC_ON_PB5 0
+
+// PB0: enable DC-DC converter
+// PB1: unconnected
+// PB2: voltage measurement
+// PB3: current-measuring resistor
+// PB4: modulation
+// PB5: reset/reserved
+
+// Signalling MODULATION on PB2
+#define BIT_MODULATION 4
+#define BIT_POWER_GOOD 0
+
+// Launch the ADC once and wait for it to finish (synchronous).
+// The 10-bit reading will be stored in the 16-bit register ADCW.
+#define adc_fire_once(){ \
+	ADCSRA |= (1 << ADSC); \
+	loop_until_bit_is_clear(ADCSRA, ADSC); \
+}
+
+
+#include "tinyqirx.c"
+
+void __attribute__ ((noinline)) qi_send_bit(qi_bit_t bit)
+{
+	if (bit != QI_500USEC_PAUSE) PORTB ^= (1 << BIT_MODULATION);
+	_delay_us(460);
+	if (bit == QI_BIT_ONE) PORTB ^= (1 << BIT_MODULATION);
+	_delay_us(460);
+}
+
+
+uint8_t __attribute__ ((noinline)) qi_measure_voltage(){
+	// - select the source of the Analog signal;
+	// - left-adjust the result
+	// - set Internal 1.1 V voltage reference.
+	ADMUX = ADC_ON_PB2 | (1 << REFS0) | (1 << ADLAR);
+
+	// Also let it run once, to initialize.
+	adc_fire_once();
+	return ADCH;
+}
+
+uint8_t __attribute__ ((noinline)) qi_measure_current(){
+	// - select the source of the Analog signal;
+	// - set Internal 1.1 V voltage reference.
+	ADMUX = ADC_ON_PB3 | (1 << REFS0);
+
+	// Also let it run once, to initialize.
+	adc_fire_once();
+	uint16_t result = ADCW;
+	return (uint8_t) result;
+}
+
+int main(){
+	// Start up the ADC:
+	{
+		// - select the source of the Analog signal;
+		// - left-adjust the result
+		// - set Internal 1.1 V voltage reference.
+		ADMUX = ADC_ON_PB2 | (1 << REFS0) | (1 << ADLAR);
+
+		// - enable the Analog-Digital converter in the Single Conversion mode; 
+		// - set the frequency to 1/16 of the CPU frequency (< 200 kHz) to
+		// ensure 10 bit conversion.
+		ADCSRA = (1 << ADEN) | 3;
+
+		// Also let it run once, to initialize.
+		adc_fire_once();
+	}
+
+
+	// Enable Write on the MODULATION pin and DC-DC enabled pin
+	DDRB |= (1 << BIT_MODULATION) | (1 << BIT_POWER_GOOD);
+	// Set them to low
+	PORTB &= ~((1 << BIT_MODULATION) | (1 << BIT_POWER_GOOD));
+
+	qi_signal_power_good(false);
+
+	// We are ready to go, set Global Enable interrupts
+	sei();
+
+	qi_connect_to_transmitter();
+	while (1){
+		if(qi_periodic_cb()) {
+			_delay_ms(300);
+			// Send POWER GOOD
+			PORTB |= (1 << BIT_POWER_GOOD);
+		} else {
+			// Turn off POWER GOOD
+			PORTB &= ~(1 << BIT_POWER_GOOD);
+		}
+	}
+
+	return 0;
+}

src/tinyqirx.c

@@ -0,0 +1,103 @@
+#include <stdint.h>
+#include <stdbool.h>
+
+
+#include "tinyqirx_utils.c"
+#include "tinyqirx_core.c"
+
+
+
+uint8_t qi_measure_voltage();
+uint8_t qi_measure_current();
+
+void qi_connect_to_transmitter(){
+	uint8_t voltage = qi_measure_voltage();
+	qi_send_signal_strength_packet(voltage, _TINYQIRX_MAXIMUM_EXPECTED_VOLTAGE_BITS);
+	qi_send_identification(_TINYQIRX_QI_MANUFACTURER_CODE, _TINYQIRX_QI_DEVICE_IDENTIFIER);
+	qi_send_configuration(_TINYQIRX_REFERENCE_POWER_BITS, _TINYQIRX_WINDOW_SIZE_BITS, _TINYQIRX_WINDOW_OFFSET_BITS);
+}
+
+#define qi_end_power_receive(error_code) qi_send_end_of_power_transfer_packet(error_code)
+
+uint8_t qi_try_restart(){
+#ifdef _TINYQIRX_TEMPERATURE_CONTROL
+	if (qi_is_battery_overheating()) {
+		return QI_EPT_OVERTEMPERATURE;
+	}
+#endif
+	uint8_t voltage_bits = qi_measure_voltage();
+	if (voltage_bits > _TINYQIRX_MAXIMUM_EXPECTED_VOLTAGE_BITS) {
+		return QI_EPT_OVERVOLTAGE;
+	}
+	uint8_t current_bits = qi_measure_current();
+	if (current_bits > _TINYQIRX_MAXIMUM_CURRENT_BITS) {
+		return QI_EPT_OVERCURRENT;
+	}
+#ifdef _TINYQIRX_CUTOFF_CURRENT_BITS
+	if (current_bits < _TINYQIRX_CUTOFF_CURRENT_BITS) {
+		return QI_EPT_CHARGE_COMPLETE;
+	}
+#endif
+	qi_send_end_of_power_transfer_packet(QI_EPT_RESTART);
+	return QI_EPT_RESTART;
+}
+
+
+bool qi_periodic_cb(){
+	uint32_t averaged_power_voltAmpereBits = 0;
+	for(int8_t sample = 0; sample < _TINYQIRX_POWER_ESTIMATION_SAMPLES; sample++){
+#ifdef _TINYQIRX_TEMPERATURE_CONTROL
+		if (qi_is_battery_overheating()) {
+			qi_send_end_of_power_transfer_packet(QI_EPT_OVERTEMPERATURE);
+			return false;
+		}
+#endif
+		uint8_t voltage_bits = qi_measure_voltage();
+
+		if (voltage_bits > _TINYQIRX_MAXIMUM_EXPECTED_VOLTAGE_BITS) {
+			qi_send_end_of_power_transfer_packet(QI_EPT_OVERVOLTAGE);
+			return false;
+		}
+		if ((voltage_bits > _TINYQIRX_VOLTAGE_TOLERANCE_RANGE_UPPER_LIMIT_BITS)
+		||  (voltage_bits < _TINYQIRX_VOLTAGE_TOLERANCE_RANGE_LOWER_LIMIT_BITS)){
+			qi_send_control_error_packet(voltage_bits, _TINYQIRX_SETPOINT_VOLTAGE_BITS);
+			// Quit sampling the power and measure the voltage rapidly instead
+			// until it converges to the allowed range
+			sample = -1;
+			continue;
+		}
+		uint8_t current_bits = qi_measure_current();
+		if (current_bits > _TINYQIRX_MAXIMUM_CURRENT_BITS) {
+			qi_send_end_of_power_transfer_packet(current_bits);
+			return false;
+		}
+#ifdef _TINYQIRX_CUTOFF_CURRENT_BITS
+		if (current_bits < _TINYQIRX_CUTOFF_CURRENT_BITS) {
+			qi_signal_power_good(false);
+			qi_send_end_of_power_transfer_packet(QI_EPT_CHARGE_COMPLETE);
+			return false;
+		}
+#endif
+		averaged_power_voltAmpereBits += voltage_bits * current_bits;
+		qi_send_bit(QI_500USEC_PAUSE);
+	}
+	uint8_t pause;
+	for (pause = 0; pause < _TINYQIRX_WINDOW_OFFSET_FILL; pause++){
+		qi_send_bit(QI_500USEC_PAUSE);
+	}
+	if (averaged_power_voltAmpereBits != 0){
+#ifdef _TINYQIRX_USE_APPROXIMATE_DIVISION
+/* Approximate division that relies on the compiler for performing the division
+ * operation and multiplies the result. For uint8_t, approximate division only
+ * differs from precise division by +/-1 at most. */
+		uint8_t averaged_power_bits = (uint8_t) ((_TINYQIRX_2_TO_24TH_DIVIDED_BY_POWER_CONVERSION_FACTOR * (averaged_power_voltAmpereBits >> _TINYQIRX_POWER_PRECISION_SHIFT)) >> 16);
+#else
+		uint8_t averaged_power_bits = (uint8_t) (averaged_power_voltAmpereBits / _TINYQIRX_POWER_CONVERSION_DIVISOR);
+#endif
+		qi_send_received_power_packet_bits(averaged_power_bits);
+	} else {
+		qi_send_received_power_packet_bits(0);
+	}
+	return true;
+}
+

src/tinyqirx_core.c

@@ -0,0 +1,139 @@
+#include <stdint.h>
+
+#include "tinyqirx_conf.auto.h"
+
+#include "tinyqirx_utils.c"
+
+#define QI_EPT_GENERIC 0x00
+#define QI_EPT_CHARGE_COMPLETE 0x01
+#define QI_EPT_INTERNAL_FAULT 0x02
+#define QI_EPT_OVERTEMPERATURE 0x03
+#define QI_EPT_OVERVOLTAGE 0x04
+#define QI_EPT_OVERCURRENT 0x05
+#define QI_EPT_BATTERY_FAILURE 0x06
+#define QI_EPT_NO_RESPONSE 0x08
+#define QI_EPT_ABORTED_NEGOTIATION 0x0A
+#define QI_EPT_RESTART 0x0B
+#define QI_EPT_REPING 0x0C
+#define QI_EPT_RFID 0x0D
+
+
+typedef enum {
+	QI_BIT_ZERO = 0,
+	QI_BIT_ONE = 1,
+	QI_500USEC_PAUSE = 0xFF
+} qi_bit_t;
+
+void qi_send_bit(qi_bit_t bit);
+
+#define qi_send_control_error_packet(actual_voltage, setpoint_voltage) { \
+	uint8_t ce_bytes[] = {0x03, ((setpoint_voltage) - (actual_voltage))}; \
+	qi_send_packet(ce_bytes, 2); \
+}
+
+
+#ifdef _TINYQIRX_USE_APPROXIMATE_DIVISION
+#define qi_send_signal_strength_packet(actual_voltage, maximum_expected_voltage) { \
+	uint8_t sig_bytes[2]; \
+	sig_bytes[0] = 0x01; /* SIG packet identifier */ \
+	if ((actual_voltage) >= (maximum_expected_voltage)) { \
+		sig_bytes[1] = 0xFF; \
+	} else { \
+	/* Approximate division that relies on the compiler for performing the division */ \
+	/* operation and multiplies the result. For uint8_t, approximate division only */ \
+	/* differs from precise division by +/-1 at most. */ \
+		sig_bytes[1] = ((uint8_t) (((_TINYQIRX_2_TO_24TH_DIVIDED_BY_MAXIMUM_EXPECTED_VOLTAGE_BITS) * ((uint16_t) actual_voltage)) >> 16)); \
+	} \
+	qi_send_packet(sig_bytes, 2); \
+}
+#else
+#define qi_send_signal_strength_packet(actual_voltage, maximum_expected_voltage) { \
+	uint8_t sig_bytes[2]; \
+	sig_bytes[0] = 0x01; /* SIG packet identifier */ \
+	if ((actual_voltage) >= (maximum_expected_voltage)) { \
+		sig_bytes[1] = 0xFF; \
+	} else { \
+		sig_bytes[1] = ((((uint16_t) (actual_voltage)) << 8) / (maximum_expected_voltage)); \
+	} \
+	qi_send_packet(sig_bytes, 2); \
+}
+#endif
+
+#define qi_send_received_power_packet_bits(actual_power_bits) { \
+	uint8_t rp8_bytes[2] = {0x04, actual_power_bits}; \
+	qi_send_packet(rp8_bytes, 2); \
+}
+
+#define qi_send_end_of_power_transfer_packet(error_code) { \
+	uint8_t ept_bytes[2]; \
+	ept_bytes[0] = 0x02; /* EPT packet identifier */ \
+	ept_bytes[1] = (error_code); \
+	qi_send_packet(ept_bytes, 2); \
+}
+
+#define qi_send_identification(manufacturer_code, device_identifier) { \
+	uint8_t id_bytes[8]; \
+	const uint8_t MAJOR_VERSION = 1; \
+	const uint8_t MINOR_VERSION = 0; \
+	id_bytes[0] = 0x71; /* ID packet identifier */ \
+	id_bytes[1] = MINOR_VERSION << 4 | MAJOR_VERSION; \
+	id_bytes[2] = (uint8_t) (manufacturer_code); \
+	id_bytes[3] = (uint8_t) ((manufacturer_code) >> 8); \
+	id_bytes[4] = (uint8_t) ((device_identifier) >> 24) & 0x7F; \
+	id_bytes[5] = (uint8_t) ((device_identifier) >> 16); \
+	id_bytes[6] = (uint8_t) ((device_identifier) >> 8); \
+	id_bytes[7] = (uint8_t) (device_identifier); \
+	qi_send_packet(id_bytes, 8); \
+}
+
+#define qi_send_configuration(reference_power, window_size, window_offset) { \
+	uint8_t cfg_bytes[6]; \
+	cfg_bytes[0] = 0x51; /* CFG packet identifier */ \
+	cfg_bytes[1] = (reference_power) & 0x3f; \
+	cfg_bytes[2] = 0x00; /* Reserved */ \
+	cfg_bytes[3] = 0x00; /* Extended protocol functionality */ \
+	cfg_bytes[4] = ((window_size) << 4) | ((window_offset) & 0x0F); \
+	cfg_bytes[5] = 0x00; /* Extended protocol functionality */ \
+	qi_send_packet(cfg_bytes, 6); \
+}
+
+void qi_send_byte(uint8_t byte){
+	qi_send_bit(QI_BIT_ZERO);
+	uint8_t parity = 1;
+	uint8_t i = 0;
+	for(i = 0; i < 8; i++){
+		qi_send_bit((qi_bit_t) (byte & 1));
+		parity ^= (byte & 1);
+		byte >>= 1;
+	}
+	qi_send_bit((qi_bit_t) parity);
+	qi_send_bit(QI_BIT_ONE);
+}
+
+void qi_send_packet(uint8_t const * const bytes, uint8_t const length){
+	uint8_t checksum = 0x00;
+	uint8_t i;
+	for(i = _TINYQIRX_PREAMBLE_LENGTH_BITS; i > 0; i--){
+		qi_send_bit(QI_BIT_ONE);
+	}
+	i = 0;
+	do {
+		uint8_t byte = bytes[i];
+		qi_send_byte(byte);
+		checksum ^= byte;
+		i++;
+	} while (i < length); 
+	qi_send_byte(checksum);
+	// This is to switch off the modulation (the last edge) + a portion of the window
+	qi_send_bit(QI_BIT_ZERO);
+	// If the packet had an odd length, we do it twice to ensure a low level
+	if ((length & 1) != 0){
+		qi_send_bit(QI_BIT_ZERO);
+	} else {
+		qi_send_bit(QI_500USEC_PAUSE);
+	}
+	for(i = 0; i < _TINYQIRX_SILENT_WINDOW_BITS - 2; i++){
+		qi_send_bit(QI_500USEC_PAUSE);
+	}
+}
+

src/tinyqirx_utils.c

@@ -0,0 +1,14 @@
+
+// https://stackoverflow.com/questions/1562074/how-do-i-show-the-value-of-a-define-at-compile-time
+#define VALUE_TO_STRING(x) #x
+#define VALUE(x) VALUE_TO_STRING(x)
+#define VAR_NAME_VALUE(var) #var "="  VALUE(var)
+
+
+
+// https://stackoverflow.com/questions/807244/c-compiler-asserts-how-to-implement
+// combine arguments (after expanding arguments)
+#define _ASSERTION_PASS 1
+#define _ASSERTION_FAIL (-1)
+#define static_assert(expr, msg) typedef char msg [(expr) ? _ASSERTION_PASS : _ASSERTION_FAIL]
+//#define static_assert(expr, msg) typedef char msg [sizeof(char[(expr) ? _ASSERTION_PASS : _ASSERTION_FAIL])]