[3/5] Add support for receiving via receive buffers. While the Intel documentation claims this is unsupported, the OS X drivers use it, causing an assertion failure since rx buffer size is 0.

diff --git a/hw/eepro100.c b/hw/eepro100.c
index 2099459..1e2f670 100644
--- a/hw/eepro100.c
+++ b/hw/eepro100.c
@@ -142,25 +142,6 @@  typedef struct {
     //~ int32_t  tx_buf_size1;  /* Length of Tx data. */
 } eepro100_tx_t;
 
-/* Receive frame descriptor. */
-typedef struct {
-    int16_t status;
-    uint16_t command;
-    uint32_t link;              /* struct RxFD * */
-    uint32_t rx_buf_addr;       /* void * */
-    uint16_t count;
-    uint16_t size;
-    char packet[MAX_ETH_FRAME_SIZE + 4];
-} eepro100_rx_t;
-
-/* Receive buffer descriptor. */
-typedef struct {
-    uint32_t count;
-    uint32_t link;
-    uint32_t buffer;
-    uint32_t size;
-} eepro100_rbd_t;
-
 typedef struct {
     uint32_t tx_good_frames, tx_max_collisions, tx_late_collisions,
         tx_underruns, tx_lost_crs, tx_deferred, tx_single_collisions,
@@ -1075,11 +1056,6 @@  static void eepro100_write_mdi(EEPRO100State * s, uint32_t val)
 #define PORT_DUMP               3
 #define PORT_SELECTION_MASK     3
 
-typedef struct {
-    uint32_t st_sign;           /* Self Test Signature */
-    uint32_t st_result;         /* Self Test Results */
-} eepro100_selftest_t;
-
 static uint32_t eepro100_read_port(EEPRO100State * s)
 {
     return 0;
@@ -1096,11 +1072,10 @@  static void eepro100_write_port(EEPRO100State * s, uint32_t val)
         break;
     case PORT_SELFTEST:
         logout("selftest address=0x%08x\n", address);
-        eepro100_selftest_t data;
-        cpu_physical_memory_read(address, (uint8_t *) & data, sizeof(data));
-        data.st_sign = 0xffffffff;
-        data.st_result = 0;
-        cpu_physical_memory_write(address, (uint8_t *) & data, sizeof(data));
+        // self-test signature, driver initializes to 0
+        stl_phys(address,     0xffffffff);
+        // self-test result (failure bitmask), driver initializes to 0xffffffff
+        stl_phys(address + 4, 0);
         break;
     case PORT_SELECTIVE_RESET:
         logout("selective reset, selftest address=0x%08x\n", address);
@@ -1523,29 +1498,30 @@  static ssize_t nic_receive(VLANClientState *vc, const uint8_t * buf, size_t size
     }
     //~ !!!
 //~ $3 = {status = 0x0, command = 0xc000, link = 0x2d220, rx_buf_addr = 0x207dc, count = 0x0, size = 0x5f8, packet = {0x0 <repeats 1518 times>}}
-    eepro100_rx_t rx;
-    cpu_physical_memory_read(s->ru_base + s->ru_offset, (uint8_t *) & rx,
-                             offsetof(eepro100_rx_t, packet));
-    uint16_t rfd_command = le16_to_cpu(rx.command);
-    uint32_t rfd_size = le16_to_cpu(rx.size);
-    uint32_t dst_addr = s->ru_base + s->ru_offset + offsetof(eepro100_rx_t, packet);
+    uint32_t rx = s->ru_base + s->ru_offset;
+    // Read and update the receive frame descriptor (RFD)
+    stw_phys (rx, rfd_status);
+    uint16_t rfd_command = lduw_phys(rx +  2);
+    s->ru_offset         = ldl_phys (rx +  4);
+    uint32_t rfd_rbd     = ldl_phys (rx +  8);
+    stw_phys (rx + 12, size);
+    uint32_t rfd_size    = lduw_phys(rx + 14);
+    uint32_t dst_addr    =           rx + 16;
     if (rfd_command & 8) {
         // argh! Flexible mode. Intel docs say it is not supported but the Mac OS driver uses it anyway.
-        eepro100_rbd_t rbd;
-        if (!s->rbd_addr)
-            s->rbd_addr = le32_to_cpu(rx.rx_buf_addr);
-        cpu_physical_memory_read(s->rbd_addr, (uint8_t *) & rbd, sizeof(rbd));
-        rfd_size = le32_to_cpu(rbd.size);
-        dst_addr = le32_to_cpu(rbd.buffer);
-        stl_phys(s->rbd_addr + offsetof(eepro100_rbd_t, count), size | 0x8000);
-        s->rbd_addr = le32_to_cpu(rbd.link);
+        // Read and update the receive buffer descriptor (RBD)
+        if (s->rbd_addr)
+            // Only the RBD address in the first RFD is valid, if we have a
+            // link value from a previous RBD follow that instead.
+            rfd_rbd = s->rbd_addr;
+        stl_phys(rfd_rbd, size | 0x8000);
+        s->rbd_addr = ldl_phys(rfd_rbd +  4);
+        dst_addr    = ldl_phys(rfd_rbd +  8);
+        rfd_size    = ldl_phys(rfd_rbd + 12);
     }
     assert(size <= rfd_size);
     logout("command 0x%04x, link 0x%08x, addr 0x%08x, size %u\n", rfd_command,
-           rx.link, rx.rx_buf_addr, rfd_size);
-    stw_phys(s->ru_base + s->ru_offset + offsetof(eepro100_rx_t, status),
-             rfd_status);
-    stw_phys(s->ru_base + s->ru_offset + offsetof(eepro100_rx_t, count), size);
+           rfd_link, rfd_rbd, rfd_size);
     /* Early receive interrupt not supported. */
     //~ eepro100_er_interrupt(s);
     /* Receive CRC Transfer not supported. */
@@ -1555,7 +1531,6 @@  static ssize_t nic_receive(VLANClientState *vc, const uint8_t * buf, size_t size
     cpu_physical_memory_write(dst_addr, buf, size);
     s->statistics.rx_good_frames++;
     eepro100_fr_interrupt(s);
-    s->ru_offset = le32_to_cpu(rx.link);
     if (rfd_command & 0x8000) {
         /* EL bit is set, so this was the last frame. */
         set_ru_state(s, ru_no_resources);