1 files changed, 88 insertions, 0 deletions
diff --git a/src/rp2040/adc.c b/src/rp2040/adc.c
new file mode 100644
index 00000000..2daf380a
--- /dev/null
+++ b/src/rp2040/adc.c
@@ -0,0 +1,88 @@
+// ADC functions on rp2040
+//
+// Copyright (C) 2021  Kevin O'Connor <kevin@koconnor.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include "board/misc.h" // timer_from_us
+#include "command.h" // shutdown
+#include "gpio.h" // gpio_adc_setup
+#include "hardware/structs/adc.h" // adc_hw
+#include "hardware/structs/padsbank0.h" // padsbank0_hw
+#include "hardware/structs/resets.h" // RESETS_RESET_ADC_BITS
+#include "internal.h" // enable_pclock
+#include "sched.h" // sched_shutdown
+
+DECL_CONSTANT("ADC_MAX", 4095);
+
+#define ADC_TEMPERATURE_PIN 0xfe
+DECL_ENUMERATION("pin", "ADC_TEMPERATURE", ADC_TEMPERATURE_PIN);
+
+struct gpio_adc
+gpio_adc_setup(uint32_t pin)
+{
+    if ((pin < 26 || pin > 29) && pin != ADC_TEMPERATURE_PIN)
+        shutdown("Not a valid ADC pin");
+
+    // Enable the ADC
+    if (!is_enabled_pclock(RESETS_RESET_ADC_BITS)) {
+        enable_pclock(RESETS_RESET_ADC_BITS);
+        adc_hw->cs = ADC_CS_EN_BITS;
+    }
+
+    uint8_t chan;
+    if (pin == ADC_TEMPERATURE_PIN) {
+        chan = 4;
+        adc_hw->cs |= ADC_CS_TS_EN_BITS;
+    } else {
+        chan = pin - 26;
+        padsbank0_hw->io[pin] = PADS_BANK0_GPIO0_OD_BITS;
+    }
+
+    return (struct gpio_adc){ .chan = 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)
+{
+    uint32_t cs = adc_hw->cs;
+    if (!(cs & ADC_CS_READY_BITS))
+        // ADC is 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;
+
+    // Begin sample
+    last_analog_read = g.chan;
+    adc_hw->cs = ((cs & ADC_CS_TS_EN_BITS) | ADC_CS_START_ONCE_BITS
+                  | ADC_CS_EN_BITS | (g.chan << ADC_CS_AINSEL_LSB));
+
+need_delay:
+    return timer_from_us(5); // Sample takes 2us but provide extra time
+}
+
+// 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_hw->result;
+}
+
+// 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;
+}