arm: async echo app

arm/uart.cc

@@ -1,5 +1,9 @@
 #include "uart.h"
 
+#include "gpio.h"
+#include "ring_buffer.h"
+#include "trace.h"
+
 namespace {
 
 constexpr uintptr_t kUart0BaseAddress = 0x40001000;
@@ -12,6 +16,10 @@ XUartLite_Config uart0_config = {
     .DataBits = 8,
 };
 
+constexpr size_t kUartTxBufferSize = 256;
+std::array<std::byte, kUartTxBufferSize> tx_buffer = {};
+RingBuffer tx_ring_buffer{.buffer = tx_buffer};
+
 }  // namespace
 
 XUartLite* uart0 = &uart0_inst;
@@ -19,3 +27,39 @@ XUartLite* uart0 = &uart0_inst;
 void InitUarts() {
     XUartLite_CfgInitialize(uart0, &uart0_config, uart0_config.RegBaseAddr);
 }
+
+extern "C" uint8_t XUartLite_GetSR(XUartLite* InstancePtr);
+#define XUL_SR_TX_FIFO_EMPTY 0x04 /* transmit FIFO empty */
+
+void UartSendCrash(std::span<const std::byte> data) {
+    while (data.size() > 0) {
+        while ((XUartLite_GetSR(uart0) & XUL_SR_TX_FIFO_EMPTY) == 0) {
+        }
+        auto* dat =
+            reinterpret_cast<uint8_t*>(const_cast<std::byte*>(data.data()));
+        uint8_t sent = XUartLite_Send(uart0, dat, data.size());
+        data = data.subspan(sent);
+    }
+    while ((XUartLite_GetSR(uart0) & XUL_SR_TX_FIFO_EMPTY) == 0) {
+    }
+}
+
+// blocking
+void UartSend(std::span<const std::byte> data) {
+    while (!tx_ring_buffer.Store(data)) {
+    }
+
+    if (!XUartLite_IsSending(uart0)) {
+        XUartLite_Send(uart0, tx_ring_buffer.RawReadPointer(),
+                       tx_ring_buffer.ContiguousAvailableData());
+    }
+}
+
+void HandleUartTxFromIsr(void*, unsigned int transmitted) {
+    tracing::trace(tracing::TraceEvent::kUartTxCb);
+    tx_ring_buffer.Pop(transmitted);
+    if (tx_ring_buffer.AvailableData() > 0) {
+        XUartLite_Send(uart0, tx_ring_buffer.RawReadPointer(),
+                       tx_ring_buffer.ContiguousAvailableData());
+    }
+}