avr: Split gpio.c into gpio.c, adc.c, hard_pwm.c, and spi.c

Split up gpio.c into multiple files in an effort to make the code a
little more understandable.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/avr/adc.c

@@ -0,0 +1,117 @@
+// Analog to Digital Converter support
+//
+// Copyright (C) 2016-2018  Kevin O'Connor <kevin@koconnor.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include "autoconf.h" // CONFIG_MACH_atmega644p
+#include "command.h" // shutdown
+#include "gpio.h" // gpio_adc_read
+#include "internal.h" // GPIO
+#include "pgm.h" // PROGMEM
+#include "sched.h" // sched_shutdown
+
+static const uint8_t adc_pins[] PROGMEM = {
+#if CONFIG_MACH_atmega168 || CONFIG_MACH_atmega328 || CONFIG_MACH_atmega328p
+    GPIO('C', 0), GPIO('C', 1), GPIO('C', 2), GPIO('C', 3),
+    GPIO('C', 4), GPIO('C', 5), GPIO('E', 0), GPIO('E', 1),
+#elif CONFIG_MACH_atmega644p || CONFIG_MACH_atmega1284p
+    GPIO('A', 0), GPIO('A', 1), GPIO('A', 2), GPIO('A', 3),
+    GPIO('A', 4), GPIO('A', 5), GPIO('A', 6), GPIO('A', 7),
+#elif CONFIG_MACH_at90usb1286 || CONFIG_MACH_at90usb646
+    GPIO('F', 0), GPIO('F', 1), GPIO('F', 2), GPIO('F', 3),
+    GPIO('F', 4), GPIO('F', 5), GPIO('F', 6), GPIO('F', 7),
+#elif CONFIG_MACH_atmega32u4
+    GPIO('F', 0), GPIO('F', 1), GPIO('F', 2), GPIO('F', 3),
+    GPIO('F', 4), GPIO('F', 5), GPIO('F', 6), GPIO('F', 7),
+    GPIO('D', 4), GPIO('D', 6), GPIO('D', 7), GPIO('B', 4),
+#elif CONFIG_MACH_atmega1280 || CONFIG_MACH_atmega2560
+    GPIO('F', 0), GPIO('F', 1), GPIO('F', 2), GPIO('F', 3),
+    GPIO('F', 4), GPIO('F', 5), GPIO('F', 6), GPIO('F', 7),
+    GPIO('K', 0), GPIO('K', 1), GPIO('K', 2), GPIO('K', 3),
+    GPIO('K', 4), GPIO('K', 5), GPIO('K', 6), GPIO('K', 7),
+#endif
+};
+
+enum { ADMUX_DEFAULT = 0x40 };
+enum { ADC_ENABLE = (1<<ADPS0)|(1<<ADPS1)|(1<<ADPS2)|(1<<ADEN)|(1<<ADIF) };
+
+DECL_CONSTANT(ADC_MAX, 1023);
+
+struct gpio_adc
+gpio_adc_setup(uint8_t pin)
+{
+    // Find pin in adc_pins table
+    uint8_t chan;
+    for (chan=0; ; chan++) {
+        if (chan >= ARRAY_SIZE(adc_pins))
+            shutdown("Not a valid ADC pin");
+        if (READP(adc_pins[chan]) == pin)
+            break;
+    }
+
+    // Enable ADC
+    ADCSRA = ADC_ENABLE;
+
+    // Disable digital input for this pin
+#ifdef DIDR2
+    if (chan >= 8)
+        DIDR2 |= 1 << (chan & 0x07);
+    else
+#endif
+        DIDR0 |= 1 << chan;
+
+    return (struct gpio_adc){ chan };
+}
+
+enum { ADC_DUMMY=0xff };
+static uint8_t last_analog_read = ADC_DUMMY;
+
+// Try to sample a value. Returns zero if sample ready, otherwise
+// returns the number of clock ticks the caller should wait before
+// retrying this function.
+uint32_t
+gpio_adc_sample(struct gpio_adc g)
+{
+    if (ADCSRA & (1<<ADSC))
+        // Busy
+        goto need_delay;
+    if (last_analog_read == g.chan)
+        // Sample now ready
+        return 0;
+    if (last_analog_read != ADC_DUMMY)
+        // Sample on another channel in progress
+        goto need_delay;
+    last_analog_read = g.chan;
+
+    // Set the channel to sample
+#if defined(ADCSRB) && defined(MUX5)
+    // The MUX5 bit of ADCSRB selects whether we're reading from
+    // channels 0 to 7 (MUX5 low) or 8 to 15 (MUX5 high).
+    ADCSRB = ((g.chan >> 3) & 0x01) << MUX5;
+#endif
+    ADMUX = ADMUX_DEFAULT | (g.chan & 0x07);
+
+    // Start the sample
+    ADCSRA = ADC_ENABLE | (1<<ADSC);
+
+    // Schedule next attempt after sample is likely to be complete
+need_delay:
+    return (13 + 1) * 128 + 200;
+}
+
+// Read a value; use only after gpio_adc_sample() returns zero
+uint16_t
+gpio_adc_read(struct gpio_adc g)
+{
+    last_analog_read = ADC_DUMMY;
+    return ADC;
+}
+
+// Cancel a sample that may have been started with gpio_adc_sample()
+void
+gpio_adc_cancel_sample(struct gpio_adc g)
+{
+    if (last_analog_read == g.chan)
+        last_analog_read = ADC_DUMMY;
+}