[Voyageurs] Create an abstraction for managing TRBs.

sys/voyageurs/xhci/trb_ring.cpp

@@ -0,0 +1,24 @@
+#include "xhci/trb_ring.h"
+
+#include <mammoth/util/debug.h>
+
+#include "xhci/trb.h"
+
+TrbRing::TrbRing() {
+  uint64_t number_trbs = 0x1000 / sizeof(XhciTrb);
+  page_ = mmth::OwnedMemoryRegion::ContiguousPhysical(0x1000, &phys_address_);
+  trb_list_ = glcr::ArrayView<XhciTrb>(
+      reinterpret_cast<XhciTrb*>(page_.vaddr()), number_trbs);
+
+  // Point the end of the command ring back to the start.
+  trb_list_[trb_list_.size() - 1] = CreateLinkTrb(phys_address_);
+}
+
+void TrbRingWriter::EnqueueTrb(const XhciTrb& trb) {
+  uint64_t ptr = enqueue_ptr_++;
+  if (enqueue_ptr_ == trb_list_.size()) {
+    crash("Not implemented: queue wrapping", glcr::UNIMPLEMENTED);
+  }
+
+  trb_list_[ptr] = trb;
+}