arm: async echo app

arm/stdlib.cc

@@ -0,0 +1,53 @@
+#include <sys/time.h>
+
+#include <cstdint>
+
+#include "itoa.h"
+#include "lock.h"
+#include "timer.h"
+#include "uart.h"
+
+extern unsigned char _heap_begin, _heap_end;
+
+namespace {
+void LogStats(unsigned char* heap) {
+    char number[] = "00000000\r\n";
+    UartSend("Program break now at 0x");
+    itoa(reinterpret_cast<int>(heap), number);
+    UartSend(number);
+}
+}  // namespace
+
+extern "C" void* _sbrk(int increment) {
+    static unsigned char* heap = &_heap_begin;
+    unsigned char* prev_heap = heap;
+    if (heap + increment >= &_heap_end) {
+        UartSend("Heap overflow!\r\n");
+        return reinterpret_cast<void*>(-1);
+    }
+    heap += increment;
+    LogStats(heap);
+    return prev_heap;
+}
+
+extern "C" int _gettimeofday(struct timeval* tv, void* tzvp) {
+    uint32_t ticks = timer0->GetT1Ticks();
+    tv->tv_sec = ticks / 100000000;
+    tv->tv_usec = (ticks % 100000000) / 100;
+
+    return 0;
+}
+
+extern "C" uint8_t __atomic_exchange_1(volatile void* ptr, uint8_t val,
+                                       int memorder) {
+    auto* dest = reinterpret_cast<volatile uint8_t*>(ptr);
+    bool ret;
+
+    {
+        InterruptLock lock;
+        ret = *dest;
+        *dest = val;
+    }
+
+    return ret;
+}