Implement ADC without hysteresis, not tested

1 files changed, 66 insertions, 2 deletions

diff --git a/firmware/src/adc.hpp b/firmware/src/adc.hpp
index a3bd0b0..ef596bc 100644
--- a/firmware/src/adc.hpp
+++ b/firmware/src/adc.hpp
@@ -1,6 +1,54 @@
 #include <array>
 #include <cstdint>
 
+namespace
+{
+
+constexpr std::uint32_t base_address               = 0x4004'c000u;
+std::uint32_t volatile * const control_status_addr = reinterpret_cast<std::uint32_t*>(base_address + 0x0u);
+std::uint32_t volatile * const result_addr         = reinterpret_cast<std::uint32_t*>(base_address + 0x4u);
+
+void
+select_input(std::uint32_t index)
+{
+    constexpr std::uint32_t ainsel = 0x111u;
+    *control_status_addr = (*control_status_addr & ~(ainsel << 12)) | ((index & ainsel) << 12);
+}
+
+bool
+ready()
+{
+    return (*control_status_addr & 1u << 8) != 0u;
+}
+
+bool
+error()
+{
+    return (*control_status_addr & 1u << 9) != 0u;
+}
+
+void
+start_once()
+{
+    *control_status_addr |= (1u << 2);
+}
+
+void
+enable(bool en)
+{
+    *control_status_addr |= en ? (1u << 2) : 0u;
+}
+
+std::uint32_t
+result()
+{
+    return *result_addr & 0x0000'0fffu;
+}
+
+std::array<std::uint32_t, 2> previous_samples { 0xffff'ffffu, 0xffff'ffffu };
+
+}
+
 namespace adc
 {
 
@@ -13,13 +61,29 @@ struct Sample
 void
 init()
 {
+    enable(true);
 }
 
 std::array<Sample, 2>
 get_samples()
 {
-    // TODO: scale 12-bit range into MIDI 7-bit range with hysteresis
-    return std::array<Sample, 2>{{{}, {}}};
+    while (!ready());
+
+    std::array<Sample, 2> samples {};
+    for (std::size_t i = 0; i < samples.size(); i++)
+    {
+        select_input(i);
+        start_once();
+
+        while (!ready());
+
+        std::uint32_t const measurement = result();
+        samples[i].changed = measurement != previous_samples[i];
+        previous_samples[i] = measurement;
+        samples[i].value = measurement * 127u / 4095u; // TODO add hysteresis
+    }
+
+    return samples;
 }
 
 }