Add Kinetis-K UART code
This was used for bringing up fet12v2 already, and seems to work nicely.
Need to either document how to use stty to configure a serial port to
interact with this or switch it to use Linux's defaults.
Change-Id: Id13bc733a53f5c723cce56b1c63c69070039fbcd
diff --git a/motors/peripheral/uart_buffer.h b/motors/peripheral/uart_buffer.h
new file mode 100644
index 0000000..fb7d126
--- /dev/null
+++ b/motors/peripheral/uart_buffer.h
@@ -0,0 +1,66 @@
+#ifndef MOTORS_PERIPHERAL_UART_BUFFER_H_
+#define MOTORS_PERIPHERAL_UART_BUFFER_H_
+
+#include <array>
+
+#include "third_party/GSL/include/gsl/gsl"
+
+namespace frc971 {
+namespace teensy {
+
+// Manages a circular buffer of data to send out.
+template<int kSize>
+class UartBuffer {
+ public:
+ // Returns the number of characters added.
+ __attribute__((warn_unused_result)) int PushSpan(gsl::span<char> data);
+
+ bool empty() const { return size_ == 0; }
+
+ // This may only be called when !empty().
+ char PopSingle();
+
+ static constexpr int size() { return kSize; }
+
+ private:
+ // The index at which we will push the next character.
+ int start_ = 0;
+ // How many characters we currently have.
+ int size_ = 0;
+
+ ::std::array<char, kSize> data_;
+};
+
+template<int kSize>
+int UartBuffer<kSize>::PushSpan(gsl::span<char> data) {
+ const int end_location = (start_ + size_) % kSize;
+ const int remaining_end = ::std::min(kSize - size_, kSize - end_location);
+ const int on_end = ::std::min<int>(data.size(), remaining_end);
+ if (on_end > 0) {
+ memcpy(&data_[end_location], data.data(), on_end);
+ }
+ size_ += on_end;
+ const int not_on_end = data.size() - on_end;
+ if (not_on_end == 0) {
+ return data.size();
+ }
+
+ const int remaining_start = ::std::min(kSize - size_, start_);
+ const int on_start = ::std::min(not_on_end, remaining_start);
+ memcpy(data_.data(), &data[on_end], on_start);
+ size_ += on_start;
+ return on_end + on_start;
+}
+
+template<int kSize>
+char UartBuffer<kSize>::PopSingle() {
+ const char r = data_[start_];
+ --size_;
+ start_ = (start_ + 1) % kSize;
+ return r;
+}
+
+} // namespace teensy
+} // namespace frc971
+
+#endif // MOTORS_PERIPHERAL_UART_BUFFER_H_