cadence_gem: initial version of device model

Device model for cadence gem ethernet controller.
Signed-off-by: NPeter A. G. Crosthwaite <peter.crosthwaite@petalogix.com>
Signed-off-by: NJohn Linn <john.linn@xilinx.com>
Acked-by: NEdgar E. Iglesias <edgar.iglesias@gmail.com>
Signed-off-by: NEdgar E. Iglesias <edgar.iglesias@gmail.com>

Makefile.target

@@ -348,6 +348,7 @@ obj-arm-y += arm_boot.o pl011.o pl031.o pl050.o pl080.o pl110.o pl181.o pl190.o
 obj-arm-y += versatile_pci.o
 obj-arm-y += cadence_uart.o
 obj-arm-y += cadence_ttc.o
+obj-arm-y += cadence_gem.o
 obj-arm-y += realview_gic.o realview.o arm_sysctl.o arm11mpcore.o a9mpcore.o
 obj-arm-y += exynos4210_gic.o exynos4210_combiner.o exynos4210.o
 obj-arm-y += exynos4_boards.o exynos4210_uart.o exynos4210_pwm.o

hw/cadence_gem.c

+/*
+ * QEMU Xilinx GEM emulation
+ *
+ * Copyright (c) 2011 Xilinx, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <zlib.h> /* For crc32 */
+
+#include "sysbus.h"
+#include "net.h"
+#include "net/checksum.h"
+
+#ifdef CADENCE_GEM_ERR_DEBUG
+#define DB_PRINT(...) do { \
+    fprintf(stderr,  ": %s: ", __func__); \
+    fprintf(stderr, ## __VA_ARGS__); \
+    } while (0);
+#else
+    #define DB_PRINT(...)
+#endif
+
+#define GEM_NWCTRL        (0x00000000/4) /* Network Control reg */
+#define GEM_NWCFG         (0x00000004/4) /* Network Config reg */
+#define GEM_NWSTATUS      (0x00000008/4) /* Network Status reg */
+#define GEM_USERIO        (0x0000000C/4) /* User IO reg */
+#define GEM_DMACFG        (0x00000010/4) /* DMA Control reg */
+#define GEM_TXSTATUS      (0x00000014/4) /* TX Status reg */
+#define GEM_RXQBASE       (0x00000018/4) /* RX Q Base address reg */
+#define GEM_TXQBASE       (0x0000001C/4) /* TX Q Base address reg */
+#define GEM_RXSTATUS      (0x00000020/4) /* RX Status reg */
+#define GEM_ISR           (0x00000024/4) /* Interrupt Status reg */
+#define GEM_IER           (0x00000028/4) /* Interrupt Enable reg */
+#define GEM_IDR           (0x0000002C/4) /* Interrupt Disable reg */
+#define GEM_IMR           (0x00000030/4) /* Interrupt Mask reg */
+#define GEM_PHYMNTNC      (0x00000034/4) /* Phy Maintaince reg */
+#define GEM_RXPAUSE       (0x00000038/4) /* RX Pause Time reg */
+#define GEM_TXPAUSE       (0x0000003C/4) /* TX Pause Time reg */
+#define GEM_TXPARTIALSF   (0x00000040/4) /* TX Partial Store and Forward */
+#define GEM_RXPARTIALSF   (0x00000044/4) /* RX Partial Store and Forward */
+#define GEM_HASHLO        (0x00000080/4) /* Hash Low address reg */
+#define GEM_HASHHI        (0x00000084/4) /* Hash High address reg */
+#define GEM_SPADDR1LO     (0x00000088/4) /* Specific addr 1 low reg */
+#define GEM_SPADDR1HI     (0x0000008C/4) /* Specific addr 1 high reg */
+#define GEM_SPADDR2LO     (0x00000090/4) /* Specific addr 2 low reg */
+#define GEM_SPADDR2HI     (0x00000094/4) /* Specific addr 2 high reg */
+#define GEM_SPADDR3LO     (0x00000098/4) /* Specific addr 3 low reg */
+#define GEM_SPADDR3HI     (0x0000009C/4) /* Specific addr 3 high reg */
+#define GEM_SPADDR4LO     (0x000000A0/4) /* Specific addr 4 low reg */
+#define GEM_SPADDR4HI     (0x000000A4/4) /* Specific addr 4 high reg */
+#define GEM_TIDMATCH1     (0x000000A8/4) /* Type ID1 Match reg */
+#define GEM_TIDMATCH2     (0x000000AC/4) /* Type ID2 Match reg */
+#define GEM_TIDMATCH3     (0x000000B0/4) /* Type ID3 Match reg */
+#define GEM_TIDMATCH4     (0x000000B4/4) /* Type ID4 Match reg */
+#define GEM_WOLAN         (0x000000B8/4) /* Wake on LAN reg */
+#define GEM_IPGSTRETCH    (0x000000BC/4) /* IPG Stretch reg */
+#define GEM_SVLAN         (0x000000C0/4) /* Stacked VLAN reg */
+#define GEM_MODID         (0x000000FC/4) /* Module ID reg */
+#define GEM_OCTTXLO       (0x00000100/4) /* Octects transmitted Low reg */
+#define GEM_OCTTXHI       (0x00000104/4) /* Octects transmitted High reg */
+#define GEM_TXCNT         (0x00000108/4) /* Error-free Frames transmitted */
+#define GEM_TXBCNT        (0x0000010C/4) /* Error-free Broadcast Frames */
+#define GEM_TXMCNT        (0x00000110/4) /* Error-free Multicast Frame */
+#define GEM_TXPAUSECNT    (0x00000114/4) /* Pause Frames Transmitted */
+#define GEM_TX64CNT       (0x00000118/4) /* Error-free 64 TX */
+#define GEM_TX65CNT       (0x0000011C/4) /* Error-free 65-127 TX */
+#define GEM_TX128CNT      (0x00000120/4) /* Error-free 128-255 TX */
+#define GEM_TX256CNT      (0x00000124/4) /* Error-free 256-511 */
+#define GEM_TX512CNT      (0x00000128/4) /* Error-free 512-1023 TX */
+#define GEM_TX1024CNT     (0x0000012C/4) /* Error-free 1024-1518 TX */
+#define GEM_TX1519CNT     (0x00000130/4) /* Error-free larger than 1519 TX */
+#define GEM_TXURUNCNT     (0x00000134/4) /* TX under run error counter */
+#define GEM_SINGLECOLLCNT (0x00000138/4) /* Single Collision Frames */
+#define GEM_MULTCOLLCNT   (0x0000013C/4) /* Multiple Collision Frames */
+#define GEM_EXCESSCOLLCNT (0x00000140/4) /* Excessive Collision Frames */
+#define GEM_LATECOLLCNT   (0x00000144/4) /* Late Collision Frames */
+#define GEM_DEFERTXCNT    (0x00000148/4) /* Deferred Transmission Frames */
+#define GEM_CSENSECNT     (0x0000014C/4) /* Carrier Sense Error Counter */
+#define GEM_OCTRXLO       (0x00000150/4) /* Octects Received register Low */
+#define GEM_OCTRXHI       (0x00000154/4) /* Octects Received register High */
+#define GEM_RXCNT         (0x00000158/4) /* Error-free Frames Received */
+#define GEM_RXBROADCNT    (0x0000015C/4) /* Error-free Broadcast Frames RX */
+#define GEM_RXMULTICNT    (0x00000160/4) /* Error-free Multicast Frames RX */
+#define GEM_RXPAUSECNT    (0x00000164/4) /* Pause Frames Received Counter */
+#define GEM_RX64CNT       (0x00000168/4) /* Error-free 64 byte Frames RX */
+#define GEM_RX65CNT       (0x0000016C/4) /* Error-free 65-127B Frames RX */
+#define GEM_RX128CNT      (0x00000170/4) /* Error-free 128-255B Frames RX */
+#define GEM_RX256CNT      (0x00000174/4) /* Error-free 256-512B Frames RX */
+#define GEM_RX512CNT      (0x00000178/4) /* Error-free 512-1023B Frames RX */
+#define GEM_RX1024CNT     (0x0000017C/4) /* Error-free 1024-1518B Frames RX */
+#define GEM_RX1519CNT     (0x00000180/4) /* Error-free 1519-max Frames RX */
+#define GEM_RXUNDERCNT    (0x00000184/4) /* Undersize Frames Received */
+#define GEM_RXOVERCNT     (0x00000188/4) /* Oversize Frames Received */
+#define GEM_RXJABCNT      (0x0000018C/4) /* Jabbers Received Counter */
+#define GEM_RXFCSCNT      (0x00000190/4) /* Frame Check seq. Error Counter */
+#define GEM_RXLENERRCNT   (0x00000194/4) /* Length Field Error Counter */
+#define GEM_RXSYMERRCNT   (0x00000198/4) /* Symbol Error Counter */
+#define GEM_RXALIGNERRCNT (0x0000019C/4) /* Alignment Error Counter */
+#define GEM_RXRSCERRCNT   (0x000001A0/4) /* Receive Resource Error Counter */
+#define GEM_RXORUNCNT     (0x000001A4/4) /* Receive Overrun Counter */
+#define GEM_RXIPCSERRCNT  (0x000001A8/4) /* IP header Checksum Error Counter */
+#define GEM_RXTCPCCNT     (0x000001AC/4) /* TCP Checksum Error Counter */
+#define GEM_RXUDPCCNT     (0x000001B0/4) /* UDP Checksum Error Counter */
+
+#define GEM_1588S         (0x000001D0/4) /* 1588 Timer Seconds */
+#define GEM_1588NS        (0x000001D4/4) /* 1588 Timer Nanoseconds */
+#define GEM_1588ADJ       (0x000001D8/4) /* 1588 Timer Adjust */
+#define GEM_1588INC       (0x000001DC/4) /* 1588 Timer Increment */
+#define GEM_PTPETXS       (0x000001E0/4) /* PTP Event Frame Transmitted (s) */
+#define GEM_PTPETXNS      (0x000001E4/4) /* PTP Event Frame Transmitted (ns) */
+#define GEM_PTPERXS       (0x000001E8/4) /* PTP Event Frame Received (s) */
+#define GEM_PTPERXNS      (0x000001EC/4) /* PTP Event Frame Received (ns) */
+#define GEM_PTPPTXS       (0x000001E0/4) /* PTP Peer Frame Transmitted (s) */
+#define GEM_PTPPTXNS      (0x000001E4/4) /* PTP Peer Frame Transmitted (ns) */
+#define GEM_PTPPRXS       (0x000001E8/4) /* PTP Peer Frame Received (s) */
+#define GEM_PTPPRXNS      (0x000001EC/4) /* PTP Peer Frame Received (ns) */
+
+/* Design Configuration Registers */
+#define GEM_DESCONF       (0x00000280/4)
+#define GEM_DESCONF2      (0x00000284/4)
+#define GEM_DESCONF3      (0x00000288/4)
+#define GEM_DESCONF4      (0x0000028C/4)
+#define GEM_DESCONF5      (0x00000290/4)
+#define GEM_DESCONF6      (0x00000294/4)
+#define GEM_DESCONF7      (0x00000298/4)
+
+#define GEM_MAXREG        (0x00000640/4) /* Last valid GEM address */
+
+/*****************************************/
+#define GEM_NWCTRL_TXSTART     0x00000200 /* Transmit Enable */
+#define GEM_NWCTRL_TXENA       0x00000008 /* Transmit Enable */
+#define GEM_NWCTRL_RXENA       0x00000004 /* Receive Enable */
+#define GEM_NWCTRL_LOCALLOOP   0x00000002 /* Local Loopback */
+
+#define GEM_NWCFG_STRIP_FCS    0x00020000 /* Strip FCS field */
+#define GEM_NWCFG_LERR_DISC    0x00010000 /* Discard RX frames with lenth err */
+#define GEM_NWCFG_BUFF_OFST_M  0x0000C000 /* Receive buffer offset mask */
+#define GEM_NWCFG_BUFF_OFST_S  14         /* Receive buffer offset shift */
+#define GEM_NWCFG_UCAST_HASH   0x00000080 /* accept unicast if hash match */
+#define GEM_NWCFG_MCAST_HASH   0x00000040 /* accept multicast if hash match */
+#define GEM_NWCFG_BCAST_REJ    0x00000020 /* Reject broadcast packets */
+#define GEM_NWCFG_PROMISC      0x00000010 /* Accept all packets */
+
+#define GEM_DMACFG_RBUFSZ_M    0x007F0000 /* DMA RX Buffer Size mask */
+#define GEM_DMACFG_RBUFSZ_S    16         /* DMA RX Buffer Size shift */
+#define GEM_DMACFG_RBUFSZ_MUL  64         /* DMA RX Buffer Size multiplier */
+#define GEM_DMACFG_TXCSUM_OFFL 0x00000800 /* Transmit checksum offload */
+
+#define GEM_TXSTATUS_TXCMPL    0x00000020 /* Transmit Complete */
+#define GEM_TXSTATUS_USED      0x00000001 /* sw owned descriptor encountered */
+
+#define GEM_RXSTATUS_FRMRCVD   0x00000002 /* Frame received */
+#define GEM_RXSTATUS_NOBUF     0x00000001 /* Buffer unavailable */
+
+/* GEM_ISR GEM_IER GEM_IDR GEM_IMR */
+#define GEM_INT_TXCMPL        0x00000080 /* Transmit Complete */
+#define GEM_INT_TXUSED         0x00000008
+#define GEM_INT_RXUSED         0x00000004
+#define GEM_INT_RXCMPL        0x00000002
+
+#define GEM_PHYMNTNC_OP_R      0x20000000 /* read operation */
+#define GEM_PHYMNTNC_OP_W      0x10000000 /* write operation */
+#define GEM_PHYMNTNC_ADDR      0x0F800000 /* Address bits */
+#define GEM_PHYMNTNC_ADDR_SHFT 23
+#define GEM_PHYMNTNC_REG       0x007C0000 /* register bits */
+#define GEM_PHYMNTNC_REG_SHIFT 18
+
+/* Marvell PHY definitions */
+#define BOARD_PHY_ADDRESS    23 /* PHY address we will emulate a device at */
+
+#define PHY_REG_CONTROL      0
+#define PHY_REG_STATUS       1
+#define PHY_REG_PHYID1       2
+#define PHY_REG_PHYID2       3
+#define PHY_REG_ANEGADV      4
+#define PHY_REG_LINKPABIL    5
+#define PHY_REG_ANEGEXP      6
+#define PHY_REG_NEXTP        7
+#define PHY_REG_LINKPNEXTP   8
+#define PHY_REG_100BTCTRL    9
+#define PHY_REG_1000BTSTAT   10
+#define PHY_REG_EXTSTAT      15
+#define PHY_REG_PHYSPCFC_CTL 16
+#define PHY_REG_PHYSPCFC_ST  17
+#define PHY_REG_INT_EN       18
+#define PHY_REG_INT_ST       19
+#define PHY_REG_EXT_PHYSPCFC_CTL  20
+#define PHY_REG_RXERR        21
+#define PHY_REG_EACD         22
+#define PHY_REG_LED          24
+#define PHY_REG_LED_OVRD     25
+#define PHY_REG_EXT_PHYSPCFC_CTL2 26
+#define PHY_REG_EXT_PHYSPCFC_ST   27
+#define PHY_REG_CABLE_DIAG   28
+
+#define PHY_REG_CONTROL_RST  0x8000
+#define PHY_REG_CONTROL_LOOP 0x4000
+#define PHY_REG_CONTROL_ANEG 0x1000
+
+#define PHY_REG_STATUS_LINK     0x0004
+#define PHY_REG_STATUS_ANEGCMPL 0x0020
+
+#define PHY_REG_INT_ST_ANEGCMPL 0x0800
+#define PHY_REG_INT_ST_LINKC    0x0400
+#define PHY_REG_INT_ST_ENERGY   0x0010
+
+/***********************************************************************/
+#define GEM_RX_REJECT  1
+#define GEM_RX_ACCEPT  0
+
+/***********************************************************************/
+
+#define DESC_1_USED 0x80000000
+#define DESC_1_LENGTH 0x00001FFF
+
+#define DESC_1_TX_WRAP 0x40000000
+#define DESC_1_TX_LAST 0x00008000
+
+#define DESC_0_RX_WRAP 0x00000002
+#define DESC_0_RX_OWNERSHIP 0x00000001
+
+#define DESC_1_RX_SOF 0x00004000
+#define DESC_1_RX_EOF 0x00008000
+
+static inline unsigned tx_desc_get_buffer(unsigned *desc)
+{
+    return desc[0];
+}
+
+static inline unsigned tx_desc_get_used(unsigned *desc)
+{
+    return (desc[1] & DESC_1_USED) ? 1 : 0;
+}
+
+static inline void tx_desc_set_used(unsigned *desc)
+{
+    desc[1] |= DESC_1_USED;
+}
+
+static inline unsigned tx_desc_get_wrap(unsigned *desc)
+{
+    return (desc[1] & DESC_1_TX_WRAP) ? 1 : 0;
+}
+
+static inline unsigned tx_desc_get_last(unsigned *desc)
+{
+    return (desc[1] & DESC_1_TX_LAST) ? 1 : 0;
+}
+
+static inline unsigned tx_desc_get_length(unsigned *desc)
+{
+    return desc[1] & DESC_1_LENGTH;
+}
+
+static inline void print_gem_tx_desc(unsigned *desc)
+{
+    DB_PRINT("TXDESC:\n");
+    DB_PRINT("bufaddr: 0x%08x\n", *desc);
+    DB_PRINT("used_hw: %d\n", tx_desc_get_used(desc));
+    DB_PRINT("wrap:    %d\n", tx_desc_get_wrap(desc));
+    DB_PRINT("last:    %d\n", tx_desc_get_last(desc));
+    DB_PRINT("length:  %d\n", tx_desc_get_length(desc));
+}
+
+static inline unsigned rx_desc_get_buffer(unsigned *desc)
+{
+    return desc[0] & ~0x3UL;
+}
+
+static inline unsigned rx_desc_get_wrap(unsigned *desc)
+{
+    return desc[0] & DESC_0_RX_WRAP ? 1 : 0;
+}
+
+static inline unsigned rx_desc_get_ownership(unsigned *desc)
+{
+    return desc[0] & DESC_0_RX_OWNERSHIP ? 1 : 0;
+}
+
+static inline void rx_desc_set_ownership(unsigned *desc)
+{
+    desc[0] |= DESC_0_RX_OWNERSHIP;
+}
+
+static inline void rx_desc_set_sof(unsigned *desc)
+{
+    desc[1] |= DESC_1_RX_SOF;
+}
+
+static inline void rx_desc_set_eof(unsigned *desc)
+{
+    desc[1] |= DESC_1_RX_EOF;
+}
+
+static inline void rx_desc_set_length(unsigned *desc, unsigned len)
+{
+    desc[1] &= ~DESC_1_LENGTH;
+    desc[1] |= len;
+}
+
+typedef struct {
+    SysBusDevice busdev;
+    MemoryRegion iomem;
+    NICState *nic;
+    NICConf conf;
+    qemu_irq irq;
+
+    /* GEM registers backing store */
+    uint32_t regs[GEM_MAXREG];
+    /* Mask of register bits which are write only */
+    uint32_t regs_wo[GEM_MAXREG];
+    /* Mask of register bits which are read only */
+    uint32_t regs_ro[GEM_MAXREG];
+    /* Mask of register bits which are clear on read */
+    uint32_t regs_rtc[GEM_MAXREG];
+    /* Mask of register bits which are write 1 to clear */
+    uint32_t regs_w1c[GEM_MAXREG];
+
+    /* PHY registers backing store */
+    uint16_t phy_regs[32];
+
+    uint8_t phy_loop; /* Are we in phy loopback? */
+
+    /* The current DMA descriptor pointers */
+    target_phys_addr_t rx_desc_addr;
+    target_phys_addr_t tx_desc_addr;
+
+} GemState;
+
+/* The broadcast MAC address: 0xFFFFFFFFFFFF */
+const uint8_t broadcast_addr[] = { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };
+
+/*
+ * gem_init_register_masks:
+ * One time initialization.
+ * Set masks to identify which register bits have magical clear properties
+ */
+static void gem_init_register_masks(GemState *s)
+{
+    /* Mask of register bits which are read only*/
+    memset(&s->regs_ro[0], 0, sizeof(s->regs_ro));
+    s->regs_ro[GEM_NWCTRL]   = 0xFFF80000;
+    s->regs_ro[GEM_NWSTATUS] = 0xFFFFFFFF;
+    s->regs_ro[GEM_DMACFG]   = 0xFE00F000;
+    s->regs_ro[GEM_TXSTATUS] = 0xFFFFFE08;
+    s->regs_ro[GEM_RXQBASE]  = 0x00000003;
+    s->regs_ro[GEM_TXQBASE]  = 0x00000003;
+    s->regs_ro[GEM_RXSTATUS] = 0xFFFFFFF0;
+    s->regs_ro[GEM_ISR]      = 0xFFFFFFFF;
+    s->regs_ro[GEM_IMR]      = 0xFFFFFFFF;
+    s->regs_ro[GEM_MODID]    = 0xFFFFFFFF;
+
+    /* Mask of register bits which are clear on read */
+    memset(&s->regs_rtc[0], 0, sizeof(s->regs_rtc));
+    s->regs_rtc[GEM_ISR]      = 0xFFFFFFFF;
+
+    /* Mask of register bits which are write 1 to clear */
+    memset(&s->regs_w1c[0], 0, sizeof(s->regs_w1c));
+    s->regs_w1c[GEM_TXSTATUS] = 0x000001F7;
+    s->regs_w1c[GEM_RXSTATUS] = 0x0000000F;
+
+    /* Mask of register bits which are write only */
+    memset(&s->regs_wo[0], 0, sizeof(s->regs_wo));
+    s->regs_wo[GEM_NWCTRL]   = 0x00073E60;
+    s->regs_wo[GEM_IER]      = 0x07FFFFFF;
+    s->regs_wo[GEM_IDR]      = 0x07FFFFFF;
+}
+
+/*
+ * phy_update_link:
+ * Make the emulated PHY link state match the QEMU "interface" state.
+ */
+static void phy_update_link(GemState *s)
+{
+    DB_PRINT("down %d\n", s->nic->nc.link_down);
+
+    /* Autonegotiation status mirrors link status.  */
+    if (s->nic->nc.link_down) {
+        s->phy_regs[PHY_REG_STATUS] &= ~(PHY_REG_STATUS_ANEGCMPL |
+                                         PHY_REG_STATUS_LINK);
+        s->phy_regs[PHY_REG_INT_ST] |= PHY_REG_INT_ST_LINKC;
+    } else {
+        s->phy_regs[PHY_REG_STATUS] |= (PHY_REG_STATUS_ANEGCMPL |
+                                         PHY_REG_STATUS_LINK);
+        s->phy_regs[PHY_REG_INT_ST] |= (PHY_REG_INT_ST_LINKC |
+                                        PHY_REG_INT_ST_ANEGCMPL |
+                                        PHY_REG_INT_ST_ENERGY);
+    }
+}
+
+static int gem_can_receive(VLANClientState *nc)
+{
+    GemState *s;
+
+    s = DO_UPCAST(NICState, nc, nc)->opaque;
+
+    DB_PRINT("\n");
+
+    /* Do nothing if receive is not enabled. */
+    if (!(s->regs[GEM_NWCTRL] & GEM_NWCTRL_RXENA)) {
+        return 0;
+    }
+
+    return 1;
+}
+
+/*
+ * gem_update_int_status:
+ * Raise or lower interrupt based on current status.
+ */
+static void gem_update_int_status(GemState *s)
+{
+    uint32_t new_interrupts = 0;
+    /* Packet transmitted ? */
+    if (s->regs[GEM_TXSTATUS] & GEM_TXSTATUS_TXCMPL) {
+        new_interrupts |= GEM_INT_TXCMPL;
+    }
+    /* End of TX ring ? */
+    if (s->regs[GEM_TXSTATUS] & GEM_TXSTATUS_USED) {
+        new_interrupts |= GEM_INT_TXUSED;
+    }
+
+    /* Frame received ? */
+    if (s->regs[GEM_RXSTATUS] & GEM_RXSTATUS_FRMRCVD) {
+        new_interrupts |= GEM_INT_RXCMPL;
+    }
+    /* RX ring full ? */
+    if (s->regs[GEM_RXSTATUS] & GEM_RXSTATUS_NOBUF) {
+        new_interrupts |= GEM_INT_RXUSED;
+    }
+
+    s->regs[GEM_ISR] |= new_interrupts & ~(s->regs[GEM_IMR]);
+
+    if (s->regs[GEM_ISR]) {
+        DB_PRINT("asserting int. (0x%08x)\n", s->regs[GEM_ISR]);
+        qemu_set_irq(s->irq, 1);
+    } else {
+        qemu_set_irq(s->irq, 0);
+    }
+}
+
+/*
+ * gem_receive_updatestats:
+ * Increment receive statistics.
+ */
+static void gem_receive_updatestats(GemState *s, const uint8_t *packet,
+                                    unsigned bytes)
+{
+    uint64_t octets;
+
+    /* Total octets (bytes) received */
+    octets = ((uint64_t)(s->regs[GEM_OCTRXLO]) << 32) |
+             s->regs[GEM_OCTRXHI];
+    octets += bytes;
+    s->regs[GEM_OCTRXLO] = octets >> 32;
+    s->regs[GEM_OCTRXHI] = octets;
+
+    /* Error-free Frames received */
+    s->regs[GEM_RXCNT]++;
+
+    /* Error-free Broadcast Frames counter */
+    if (!memcmp(packet, broadcast_addr, 6)) {
+        s->regs[GEM_RXBROADCNT]++;
+    }
+
+    /* Error-free Multicast Frames counter */
+    if (packet[0] == 0x01) {
+        s->regs[GEM_RXMULTICNT]++;
+    }
+
+    if (bytes <= 64) {
+        s->regs[GEM_RX64CNT]++;
+    } else if (bytes <= 127) {
+        s->regs[GEM_RX65CNT]++;
+    } else if (bytes <= 255) {
+        s->regs[GEM_RX128CNT]++;
+    } else if (bytes <= 511) {
+        s->regs[GEM_RX256CNT]++;
+    } else if (bytes <= 1023) {
+        s->regs[GEM_RX512CNT]++;
+    } else if (bytes <= 1518) {
+        s->regs[GEM_RX1024CNT]++;
+    } else {
+        s->regs[GEM_RX1519CNT]++;
+    }
+}
+
+/*
+ * Get the MAC Address bit from the specified position
+ */
+static unsigned get_bit(const uint8_t *mac, unsigned bit)
+{
+    unsigned byte;
+
+    byte = mac[bit / 8];
+    byte >>= (bit & 0x7);
+    byte &= 1;
+
+    return byte;
+}
+
+/*
+ * Calculate a GEM MAC Address hash index
+ */
+static unsigned calc_mac_hash(const uint8_t *mac)
+{
+    int index_bit, mac_bit;
+    unsigned hash_index;
+
+    hash_index = 0;
+    mac_bit = 5;
+    for (index_bit = 5; index_bit >= 0; index_bit--) {
+        hash_index |= (get_bit(mac,  mac_bit) ^
+                               get_bit(mac, mac_bit + 6) ^
+                               get_bit(mac, mac_bit + 12) ^
+                               get_bit(mac, mac_bit + 18) ^
+                               get_bit(mac, mac_bit + 24) ^
+                               get_bit(mac, mac_bit + 30) ^
+                               get_bit(mac, mac_bit + 36) ^
+                               get_bit(mac, mac_bit + 42)) << index_bit;
+        mac_bit--;
+    }
+
+    return hash_index;
+}
+
+/*
+ * gem_mac_address_filter:
+ * Accept or reject this destination address?
+ * Returns:
+ * GEM_RX_REJECT: reject
+ * GEM_RX_ACCEPT: accept
+ */
+static int gem_mac_address_filter(GemState *s, const uint8_t *packet)
+{
+    uint8_t *gem_spaddr;
+    int i;
+
+    /* Promiscuous mode? */
+    if (s->regs[GEM_NWCFG] & GEM_NWCFG_PROMISC) {
+        return GEM_RX_ACCEPT;
+    }
+
+    if (!memcmp(packet, broadcast_addr, 6)) {
+        /* Reject broadcast packets? */
+        if (s->regs[GEM_NWCFG] & GEM_NWCFG_BCAST_REJ) {
+            return GEM_RX_REJECT;
+        }
+        return GEM_RX_ACCEPT;
+    }
+
+    /* Accept packets -w- hash match? */
+    if ((packet[0] == 0x01 && (s->regs[GEM_NWCFG] & GEM_NWCFG_MCAST_HASH)) ||
+        (packet[0] != 0x01 && (s->regs[GEM_NWCFG] & GEM_NWCFG_UCAST_HASH))) {
+        unsigned hash_index;
+
+        hash_index = calc_mac_hash(packet);
+        if (hash_index < 32) {
+            if (s->regs[GEM_HASHLO] & (1<<hash_index)) {
+                return GEM_RX_ACCEPT;
+            }
+        } else {
+            hash_index -= 32;
+            if (s->regs[GEM_HASHHI] & (1<<hash_index)) {
+                return GEM_RX_ACCEPT;
+            }
+        }
+    }
+
+    /* Check all 4 specific addresses */
+    gem_spaddr = (uint8_t *)&(s->regs[GEM_SPADDR1LO]);
+    for (i = 0; i < 4; i++) {
+        if (!memcmp(packet, gem_spaddr, 6)) {
+            return GEM_RX_ACCEPT;
+        }
+
+        gem_spaddr += 8;
+    }
+
+    /* No address match; reject the packet */
+    return GEM_RX_REJECT;
+}
+
+/*
+ * gem_receive:
+ * Fit a packet handed to us by QEMU into the receive descriptor ring.
+ */
+static ssize_t gem_receive(VLANClientState *nc, const uint8_t *buf, size_t size)
+{
+    unsigned    desc[2];
+    target_phys_addr_t packet_desc_addr, last_desc_addr;
+    GemState *s;
+    unsigned   rxbufsize, bytes_to_copy;
+    unsigned   rxbuf_offset;
+    uint8_t    rxbuf[2048];
+    uint8_t   *rxbuf_ptr;
+
+    s = DO_UPCAST(NICState, nc, nc)->opaque;
+
+    /* Do nothing if receive is not enabled. */
+    if (!(s->regs[GEM_NWCTRL] & GEM_NWCTRL_RXENA)) {
+        return -1;
+    }
+
+    /* Is this destination MAC address "for us" ? */
+    if (gem_mac_address_filter(s, buf) == GEM_RX_REJECT) {
+        return -1;
+    }
+
+    /* Discard packets with receive length error enabled ? */
+    if (s->regs[GEM_NWCFG] & GEM_NWCFG_LERR_DISC) {
+        unsigned type_len;
+
+        /* Fish the ethertype / length field out of the RX packet */
+        type_len = buf[12] << 8 | buf[13];
+        /* It is a length field, not an ethertype */
+        if (type_len < 0x600) {
+            if (size < type_len) {
+                /* discard */
+                return -1;
+            }
+        }
+    }
+
+    /*
+     * Determine configured receive buffer offset (probably 0)
+     */
+    rxbuf_offset = (s->regs[GEM_NWCFG] & GEM_NWCFG_BUFF_OFST_M) >>
+                   GEM_NWCFG_BUFF_OFST_S;
+
+    /* The configure size of each receive buffer.  Determines how many
+     * buffers needed to hold this packet.
+     */
+    rxbufsize = ((s->regs[GEM_DMACFG] & GEM_DMACFG_RBUFSZ_M) >>
+                 GEM_DMACFG_RBUFSZ_S) * GEM_DMACFG_RBUFSZ_MUL;
+    bytes_to_copy = size;
+
+    /* Strip of FCS field ? (usually yes) */
+    if (s->regs[GEM_NWCFG] & GEM_NWCFG_STRIP_FCS) {
+        rxbuf_ptr = (void *)buf;
+    } else {
+        unsigned crc_val;
+        int      crc_offset;
+
+        /* The application wants the FCS field, which QEMU does not provide.
+         * We must try and caclculate one.
+         */
+
+        memcpy(rxbuf, buf, size);
+        memset(rxbuf + size, 0, sizeof(rxbuf - size));
+        rxbuf_ptr = rxbuf;
+        crc_val = cpu_to_le32(crc32(0, rxbuf, MAX(size, 60)));
+        if (size < 60) {
+            crc_offset = 60;
+        } else {
+            crc_offset = size;
+        }
+        memcpy(rxbuf + crc_offset, &crc_val, sizeof(crc_val));
+
+        bytes_to_copy += 4;
+        size += 4;
+    }
+
+    /* Pad to minimum length */
+    if (size < 64) {
+        size = 64;
+    }
+
+    DB_PRINT("config bufsize: %d packet size: %ld\n", rxbufsize, size);
+
+    packet_desc_addr = s->rx_desc_addr;
+    while (1) {
+        DB_PRINT("read descriptor 0x%x\n", packet_desc_addr);
+        /* read current descriptor */
+        cpu_physical_memory_read(packet_desc_addr,
+                                 (uint8_t *)&desc[0], sizeof(desc));
+
+        /* Descriptor owned by software ? */
+        if (rx_desc_get_ownership(desc) == 1) {
+            DB_PRINT("descriptor 0x%x owned by sw.\n", packet_desc_addr);
+            s->regs[GEM_RXSTATUS] |= GEM_RXSTATUS_NOBUF;
+            /* Handle interrupt consequences */
+            gem_update_int_status(s);
+            return -1;
+        }
+
+        DB_PRINT("copy %d bytes to 0x%x\n", MIN(bytes_to_copy, rxbufsize),
+                rx_desc_get_buffer(desc));
+
+        /*
+         * Let's have QEMU lend a helping hand.
+         */
+        if (rx_desc_get_buffer(desc) == 0) {
+            DB_PRINT("Invalid RX buffer (NULL) for descriptor 0x%x\n",
+                       packet_desc_addr);
+            break;
+        }
+
+        /* Copy packet data to emulated DMA buffer */
+        cpu_physical_memory_write(rx_desc_get_buffer(desc) + rxbuf_offset,
+                                  rxbuf_ptr, MIN(bytes_to_copy, rxbufsize));
+        bytes_to_copy -= MIN(bytes_to_copy, rxbufsize);
+        rxbuf_ptr += MIN(bytes_to_copy, rxbufsize);
+        if (bytes_to_copy == 0) {
+            break;
+        }
+
+        /* Next descriptor */
+        if (rx_desc_get_wrap(desc)) {
+            packet_desc_addr = s->regs[GEM_RXQBASE];
+        } else {
+            packet_desc_addr += 8;
+        }
+    }
+
+    DB_PRINT("set length: %ld, EOF on descriptor 0x%x\n", size,
+            (unsigned)packet_desc_addr);
+
+    /* Update last descriptor with EOF and total length */
+    rx_desc_set_eof(desc);
+    rx_desc_set_length(desc, size);
+    cpu_physical_memory_write(packet_desc_addr,
+                              (uint8_t *)&desc[0], sizeof(desc));
+
+    /* Advance RX packet descriptor Q */
+    last_desc_addr = packet_desc_addr;
+    packet_desc_addr = s->rx_desc_addr;
+    s->rx_desc_addr = last_desc_addr;
+    if (rx_desc_get_wrap(desc)) {
+        s->rx_desc_addr = s->regs[GEM_RXQBASE];
+    } else {
+        s->rx_desc_addr += 8;
+    }
+
+    DB_PRINT("set SOF, OWN on descriptor 0x%08x\n", packet_desc_addr);
+
+    /* Count it */
+    gem_receive_updatestats(s, buf, size);
+
+    /* Update first descriptor (which could also be the last) */
+    /* read descriptor */
+    cpu_physical_memory_read(packet_desc_addr,
+                             (uint8_t *)&desc[0], sizeof(desc));
+    rx_desc_set_sof(desc);
+    rx_desc_set_ownership(desc);
+    cpu_physical_memory_write(packet_desc_addr,
+                              (uint8_t *)&desc[0], sizeof(desc));
+
+    s->regs[GEM_RXSTATUS] |= GEM_RXSTATUS_FRMRCVD;
+
+    /* Handle interrupt consequences */
+    gem_update_int_status(s);
+
+    return size;
+}
+
+/*
+ * gem_transmit_updatestats:
+ * Increment transmit statistics.
+ */
+static void gem_transmit_updatestats(GemState *s, const uint8_t *packet,
+                                     unsigned bytes)
+{
+    uint64_t octets;
+
+    /* Total octets (bytes) transmitted */
+    octets = ((uint64_t)(s->regs[GEM_OCTTXLO]) << 32) |
+             s->regs[GEM_OCTTXHI];
+    octets += bytes;
+    s->regs[GEM_OCTTXLO] = octets >> 32;
+    s->regs[GEM_OCTTXHI] = octets;
+
+    /* Error-free Frames transmitted */
+    s->regs[GEM_TXCNT]++;
+
+    /* Error-free Broadcast Frames counter */
+    if (!memcmp(packet, broadcast_addr, 6)) {
+        s->regs[GEM_TXBCNT]++;
+    }
+
+    /* Error-free Multicast Frames counter */
+    if (packet[0] == 0x01) {
+        s->regs[GEM_TXMCNT]++;
+    }
+
+    if (bytes <= 64) {
+        s->regs[GEM_TX64CNT]++;
+    } else if (bytes <= 127) {
+        s->regs[GEM_TX65CNT]++;
+    } else if (bytes <= 255) {
+        s->regs[GEM_TX128CNT]++;
+    } else if (bytes <= 511) {
+        s->regs[GEM_TX256CNT]++;
+    } else if (bytes <= 1023) {
+        s->regs[GEM_TX512CNT]++;
+    } else if (bytes <= 1518) {
+        s->regs[GEM_TX1024CNT]++;
+    } else {
+        s->regs[GEM_TX1519CNT]++;
+    }
+}
+
+/*
+ * gem_transmit:
+ * Fish packets out of the descriptor ring and feed them to QEMU
+ */
+static void gem_transmit(GemState *s)
+{
+    unsigned    desc[2];
+    target_phys_addr_t packet_desc_addr;
+    uint8_t     tx_packet[2048];
+    uint8_t     *p;
+    unsigned    total_bytes;
+
+    /* Do nothing if transmit is not enabled. */
+    if (!(s->regs[GEM_NWCTRL] & GEM_NWCTRL_TXENA)) {
+        return;
+    }
+
+    DB_PRINT("\n");
+
+    /* The packet we will hand off to qemu.
+     * Packets scattered across multiple descriptors are gathered to this
+     * one contiguous buffer first.
+     */
+    p = tx_packet;
+    total_bytes = 0;
+
+    /* read current descriptor */
+    packet_desc_addr = s->tx_desc_addr;
+    cpu_physical_memory_read(packet_desc_addr,
+                             (uint8_t *)&desc[0], sizeof(desc));
+    /* Handle all descriptors owned by hardware */
+    while (tx_desc_get_used(desc) == 0) {
+
+        /* Do nothing if transmit is not enabled. */
+        if (!(s->regs[GEM_NWCTRL] & GEM_NWCTRL_TXENA)) {
+            return;
+        }
+        print_gem_tx_desc(desc);
+
+        /* The real hardware would eat this (and possibly crash).
+         * For QEMU let's lend a helping hand.
+         */
+        if ((tx_desc_get_buffer(desc) == 0) ||
+            (tx_desc_get_length(desc) == 0)) {
+            DB_PRINT("Invalid TX descriptor @ 0x%x\n", packet_desc_addr);
+            break;
+        }
+
+        /* Gather this fragment of the packet from "dma memory" to our contig.
+         * buffer.
+         */
+        cpu_physical_memory_read(tx_desc_get_buffer(desc), p,
+                                 tx_desc_get_length(desc));
+        p += tx_desc_get_length(desc);
+        total_bytes += tx_desc_get_length(desc);
+
+        /* Last descriptor for this packet; hand the whole thing off */
+        if (tx_desc_get_last(desc)) {
+            /* Modify the 1st descriptor of this packet to be owned by
+             * the processor.
+             */
+            cpu_physical_memory_read(s->tx_desc_addr,
+                                     (uint8_t *)&desc[0], sizeof(desc));
+            tx_desc_set_used(desc);
+            cpu_physical_memory_write(s->tx_desc_addr,
+                                      (uint8_t *)&desc[0], sizeof(desc));
+            /* Advance the hardare current descriptor past this packet */
+            if (tx_desc_get_wrap(desc)) {
+                s->tx_desc_addr = s->regs[GEM_TXQBASE];
+            } else {
+                s->tx_desc_addr = packet_desc_addr + 8;
+            }
+            DB_PRINT("TX descriptor next: 0x%08x\n", s->tx_desc_addr);
+
+            s->regs[GEM_TXSTATUS] |= GEM_TXSTATUS_TXCMPL;
+
+            /* Handle interrupt consequences */
+            gem_update_int_status(s);
+
+            /* Is checksum offload enabled? */
+            if (s->regs[GEM_DMACFG] & GEM_DMACFG_TXCSUM_OFFL) {
+                net_checksum_calculate(tx_packet, total_bytes);
+            }
+
+            /* Update MAC statistics */
+            gem_transmit_updatestats(s, tx_packet, total_bytes);
+
+            /* Send the packet somewhere */
+            if (s->phy_loop) {
+                gem_receive(&s->nic->nc, tx_packet, total_bytes);
+            } else {
+                qemu_send_packet(&s->nic->nc, tx_packet, total_bytes);
+            }
+
+            /* Prepare for next packet */
+            p = tx_packet;
+            total_bytes = 0;
+        }
+
+        /* read next descriptor */
+        if (tx_desc_get_wrap(desc)) {
+            packet_desc_addr = s->regs[GEM_TXQBASE];
+        } else {
+            packet_desc_addr += 8;
+        }
+        cpu_physical_memory_read(packet_desc_addr,
+                                 (uint8_t *)&desc[0], sizeof(desc));
+    }
+
+    if (tx_desc_get_used(desc)) {
+        s->regs[GEM_TXSTATUS] |= GEM_TXSTATUS_USED;
+        gem_update_int_status(s);
+    }
+}
+
+static void gem_phy_reset(GemState *s)
+{
+    memset(&s->phy_regs[0], 0, sizeof(s->phy_regs));
+    s->phy_regs[PHY_REG_CONTROL] = 0x1140;
+    s->phy_regs[PHY_REG_STATUS] = 0x7969;
+    s->phy_regs[PHY_REG_PHYID1] = 0x0141;
+    s->phy_regs[PHY_REG_PHYID2] = 0x0CC2;
+    s->phy_regs[PHY_REG_ANEGADV] = 0x01E1;
+    s->phy_regs[PHY_REG_LINKPABIL] = 0xCDE1;
+    s->phy_regs[PHY_REG_ANEGEXP] = 0x000F;
+    s->phy_regs[PHY_REG_NEXTP] = 0x2001;
+    s->phy_regs[PHY_REG_LINKPNEXTP] = 0x40E6;
+    s->phy_regs[PHY_REG_100BTCTRL] = 0x0300;
+    s->phy_regs[PHY_REG_1000BTSTAT] = 0x7C00;
+    s->phy_regs[PHY_REG_EXTSTAT] = 0x3000;
+    s->phy_regs[PHY_REG_PHYSPCFC_CTL] = 0x0078;
+    s->phy_regs[PHY_REG_PHYSPCFC_ST] = 0xBC00;
+    s->phy_regs[PHY_REG_EXT_PHYSPCFC_CTL] = 0x0C60;
+    s->phy_regs[PHY_REG_LED] = 0x4100;
+    s->phy_regs[PHY_REG_EXT_PHYSPCFC_CTL2] = 0x000A;
+    s->phy_regs[PHY_REG_EXT_PHYSPCFC_ST] = 0x848B;
+
+    phy_update_link(s);
+}
+
+static void gem_reset(DeviceState *d)
+{
+    GemState *s = FROM_SYSBUS(GemState, sysbus_from_qdev(d));
+
+    DB_PRINT("\n");
+
+    /* Set post reset register values */
+    memset(&s->regs[0], 0, sizeof(s->regs));
+    s->regs[GEM_NWCFG] = 0x00080000;
+    s->regs[GEM_NWSTATUS] = 0x00000006;
+    s->regs[GEM_DMACFG] = 0x00020784;
+    s->regs[GEM_IMR] = 0x07ffffff;
+    s->regs[GEM_TXPAUSE] = 0x0000ffff;
+    s->regs[GEM_TXPARTIALSF] = 0x000003ff;
+    s->regs[GEM_RXPARTIALSF] = 0x000003ff;
+    s->regs[GEM_MODID] = 0x00020118;
+    s->regs[GEM_DESCONF] = 0x02500111;
+    s->regs[GEM_DESCONF2] = 0x2ab13fff;
+    s->regs[GEM_DESCONF5] = 0x002f2145;
+    s->regs[GEM_DESCONF6] = 0x00000200;
+
+    gem_phy_reset(s);
+
+    gem_update_int_status(s);
+}
+
+static uint16_t gem_phy_read(GemState *s, unsigned reg_num)
+{
+    DB_PRINT("reg: %d value: 0x%04x\n", reg_num, s->phy_regs[reg_num]);
+    return s->phy_regs[reg_num];
+}
+
+static void gem_phy_write(GemState *s, unsigned reg_num, uint16_t val)
+{
+    DB_PRINT("reg: %d value: 0x%04x\n", reg_num, val);
+
+    switch (reg_num) {
+    case PHY_REG_CONTROL:
+        if (val & PHY_REG_CONTROL_RST) {
+            /* Phy reset */
+            gem_phy_reset(s);
+            val &= ~(PHY_REG_CONTROL_RST | PHY_REG_CONTROL_LOOP);
+            s->phy_loop = 0;
+        }
+        if (val & PHY_REG_CONTROL_ANEG) {
+            /* Complete autonegotiation immediately */
+            val &= ~PHY_REG_CONTROL_ANEG;
+            s->phy_regs[PHY_REG_STATUS] |= PHY_REG_STATUS_ANEGCMPL;
+        }
+        if (val & PHY_REG_CONTROL_LOOP) {
+            DB_PRINT("PHY placed in loopback\n");
+            s->phy_loop = 1;
+        } else {
+            s->phy_loop = 0;
+        }
+        break;
+    }
+    s->phy_regs[reg_num] = val;
+}
+
+/*
+ * gem_read32:
+ * Read a GEM register.
+ */
+static uint64_t gem_read(void *opaque, target_phys_addr_t offset, unsigned size)
+{
+    GemState *s;
+    uint32_t retval;
+
+    s = (GemState *)opaque;
+
+    offset >>= 2;
+    retval = s->regs[offset];
+
+    DB_PRINT("offset: 0x%04x read: 0x%08x\n", offset*4, retval);
+
+    switch (offset) {
+    case GEM_ISR:
+        qemu_set_irq(s->irq, 0);
+        break;
+    case GEM_PHYMNTNC:
+        if (retval & GEM_PHYMNTNC_OP_R) {
+            uint32_t phy_addr, reg_num;
+
+            phy_addr = (retval & GEM_PHYMNTNC_ADDR) >> GEM_PHYMNTNC_ADDR_SHFT;
+            if (phy_addr == BOARD_PHY_ADDRESS) {
+                reg_num = (retval & GEM_PHYMNTNC_REG) >> GEM_PHYMNTNC_REG_SHIFT;
+                retval &= 0xFFFF0000;
+                retval |= gem_phy_read(s, reg_num);
+            } else {
+                retval |= 0xFFFF; /* No device at this address */
+            }
+        }
+        break;
+    }
+
+    /* Squash read to clear bits */
+    s->regs[offset] &= ~(s->regs_rtc[offset]);
+
+    /* Do not provide write only bits */
+    retval &= ~(s->regs_wo[offset]);
+
+    DB_PRINT("0x%08x\n", retval);
+    return retval;
+}
+
+/*
+ * gem_write32:
+ * Write a GEM register.
+ */
+static void gem_write(void *opaque, target_phys_addr_t offset, uint64_t val,
+        unsigned size)
+{
+    GemState *s = (GemState *)opaque;
+    uint32_t readonly;
+
+    DB_PRINT("offset: 0x%04x write: 0x%08x ", offset, (unsigned)val);
+    offset >>= 2;
+
+    /* Squash bits which are read only in write value */
+    val &= ~(s->regs_ro[offset]);
+    /* Preserve (only) bits which are read only in register */
+    readonly = s->regs[offset];
+    readonly &= s->regs_ro[offset];
+
+    /* Squash bits which are write 1 to clear */
+    val &= ~(s->regs_w1c[offset] & val);
+
+    /* Copy register write to backing store */
+    s->regs[offset] = val | readonly;
+
+    /* Handle register write side effects */
+    switch (offset) {
+    case GEM_NWCTRL:
+        if (val & GEM_NWCTRL_TXSTART) {
+            gem_transmit(s);
+        }
+        if (!(val & GEM_NWCTRL_TXENA)) {
+            /* Reset to start of Q when transmit disabled. */
+            s->tx_desc_addr = s->regs[GEM_TXQBASE];
+        }
+        if (!(val & GEM_NWCTRL_RXENA)) {
+            /* Reset to start of Q when receive disabled. */
+            s->rx_desc_addr = s->regs[GEM_RXQBASE];
+        }
+        break;
+
+    case GEM_TXSTATUS:
+        gem_update_int_status(s);
+        break;
+    case GEM_RXQBASE:
+        s->rx_desc_addr = val;
+        break;
+    case GEM_TXQBASE:
+        s->tx_desc_addr = val;
+        break;
+    case GEM_RXSTATUS:
+        gem_update_int_status(s);
+        break;
+    case GEM_IER:
+        s->regs[GEM_IMR] &= ~val;
+        gem_update_int_status(s);
+        break;
+    case GEM_IDR:
+        s->regs[GEM_IMR] |= val;
+        gem_update_int_status(s);
+        break;
+    case GEM_PHYMNTNC:
+        if (val & GEM_PHYMNTNC_OP_W) {
+            uint32_t phy_addr, reg_num;
+
+            phy_addr = (val & GEM_PHYMNTNC_ADDR) >> GEM_PHYMNTNC_ADDR_SHFT;
+            if (phy_addr == BOARD_PHY_ADDRESS) {
+                reg_num = (val & GEM_PHYMNTNC_REG) >> GEM_PHYMNTNC_REG_SHIFT;
+                gem_phy_write(s, reg_num, val);
+            }
+        }
+        break;
+    }
+
+    DB_PRINT("newval: 0x%08x\n", s->regs[offset]);
+}
+
+static const MemoryRegionOps gem_ops = {
+    .read = gem_read,
+    .write = gem_write,
+    .endianness = DEVICE_LITTLE_ENDIAN,
+};
+
+static void gem_cleanup(VLANClientState *nc)
+{
+    GemState *s = DO_UPCAST(NICState, nc, nc)->opaque;
+
+    DB_PRINT("\n");
+    s->nic = NULL;
+}
+
+static void gem_set_link(VLANClientState *nc)
+{
+    DB_PRINT("\n");
+    phy_update_link(DO_UPCAST(NICState, nc, nc)->opaque);
+}
+
+static NetClientInfo net_gem_info = {
+    .type = NET_CLIENT_TYPE_NIC,
+    .size = sizeof(NICState),
+    .can_receive = gem_can_receive,
+    .receive = gem_receive,
+    .cleanup = gem_cleanup,
+    .link_status_changed = gem_set_link,
+};
+
+static int gem_init(SysBusDevice *dev)
+{
+    GemState *s;
+
+    DB_PRINT("\n");
+
+    s = FROM_SYSBUS(GemState, dev);
+    gem_init_register_masks(s);
+    memory_region_init_io(&s->iomem, &gem_ops, s, "enet", sizeof(s->regs));
+    sysbus_init_mmio(dev, &s->iomem);
+    sysbus_init_irq(dev, &s->irq);
+    qemu_macaddr_default_if_unset(&s->conf.macaddr);
+
+    s->nic = qemu_new_nic(&net_gem_info, &s->conf,
+            object_get_typename(OBJECT(dev)), dev->qdev.id, s);
+
+    return 0;
+}
+
+static const VMStateDescription vmstate_cadence_gem = {
+    .name = "cadence_gem",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .minimum_version_id_old = 1,
+    .fields      = (VMStateField[]) {
+        VMSTATE_UINT32_ARRAY(regs, GemState, GEM_MAXREG),
+        VMSTATE_UINT16_ARRAY(phy_regs, GemState, 32),
+        VMSTATE_UINT8(phy_loop, GemState),
+        VMSTATE_UINT32(rx_desc_addr, GemState),
+        VMSTATE_UINT32(tx_desc_addr, GemState),
+    }
+};
+
+static Property gem_properties[] = {
+    DEFINE_NIC_PROPERTIES(GemState, conf),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
+static void gem_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+    SysBusDeviceClass *sdc = SYS_BUS_DEVICE_CLASS(klass);
+
+    sdc->init = gem_init;
+    dc->props = gem_properties;
+    dc->vmsd = &vmstate_cadence_gem;
+    dc->reset = gem_reset;
+}
+
+static TypeInfo gem_info = {
+    .class_init = gem_class_init,
+    .name  = "cadence_gem",
+    .parent = TYPE_SYS_BUS_DEVICE,
+    .instance_size  = sizeof(GemState),
+};
+
+static void gem_register_types(void)
+{
+    type_register_static(&gem_info);
+}
+
+type_init(gem_register_types)