wifi:

* don't receive packets if the RX buffer is zero-sized
* avoid potential out-of-bound writes

src/Wifi.cpp

@@ -816,6 +816,9 @@ bool CheckRX(bool block)
     if (!(IOPORT(W_RXCnt) & 0x8000))
         return false;
 
+    if (IOPORT(W_RXBufBegin) == IOPORT(W_RXBufEnd))
+        return false;
+
     u16 framelen;
     u16 framectl;
     u8 txrate;
@@ -1049,7 +1052,7 @@ void USTimer(u32 param)
         if (!(RXTime & RXHalfwordTimeMask))
         {
             u16 addr = IOPORT(W_RXTXAddr) << 1;
-            *(u16*)&RAM[addr] = *(u16*)&RXBuffer[RXBufferPtr];
+            if (addr < 0x1FFF) *(u16*)&RAM[addr] = *(u16*)&RXBuffer[RXBufferPtr];
 
             IncrementRXAddr(addr);
             RXBufferPtr += 2;
@@ -1146,7 +1149,7 @@ void RFTransfer_Type3()
 // TODO: wifi waitstates
 
 u16 Read(u32 addr)
-{
+{//printf("WIFI READ %08X\n", addr);
     if (addr >= 0x04810000)
         return 0;
 
@@ -1236,7 +1239,7 @@ u16 Read(u32 addr)
 }
 
 void Write(u32 addr, u16 val)
-{
+{//printf("WIFI WRITE %08X %04X\n", addr, val);
     if (addr >= 0x04810000)
         return;