Archipelago » qemu

/*

 * PowerMac descriptor-based DMA emulation

 *

 * Copyright (c) 2005-2007 Fabrice Bellard

 * Copyright (c) 2007 Jocelyn Mayer

 * Copyright (c) 2009 Laurent Vivier

 *

 * some parts from linux-2.6.28, arch/powerpc/include/asm/dbdma.h

 *

 *   Definitions for using the Apple Descriptor-Based DMA controller

 *   in Power Macintosh computers.

 *

 *   Copyright (C) 1996 Paul Mackerras.

 *

 * some parts from mol 0.9.71

 *

 *   Descriptor based DMA emulation

 *

 *   Copyright (C) 1998-2004 Samuel Rydh (samuel@ibrium.se)

 *

 * 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 "hw.h"

#include "isa.h"

#include "mac_dbdma.h"

/* debug DBDMA */

//#define DEBUG_DBDMA

#ifdef DEBUG_DBDMA

#define DBDMA_DPRINTF(fmt, ...)                                 \

    do { printf("DBDMA: " fmt , ## __VA_ARGS__); } while (0)

#else

#define DBDMA_DPRINTF(fmt, ...)

#endif

/*

 */

/*

 * DBDMA control/status registers.  All little-endian.

 */

#define DBDMA_CONTROL         0x00

#define DBDMA_STATUS          0x01

#define DBDMA_CMDPTR_HI       0x02

#define DBDMA_CMDPTR_LO       0x03

#define DBDMA_INTR_SEL        0x04

#define DBDMA_BRANCH_SEL      0x05

#define DBDMA_WAIT_SEL        0x06

#define DBDMA_XFER_MODE       0x07

#define DBDMA_DATA2PTR_HI     0x08

#define DBDMA_DATA2PTR_LO     0x09

#define DBDMA_RES1            0x0A

#define DBDMA_ADDRESS_HI      0x0B

#define DBDMA_BRANCH_ADDR_HI  0x0C

#define DBDMA_RES2            0x0D

#define DBDMA_RES3            0x0E

#define DBDMA_RES4            0x0F

#define DBDMA_REGS            16

#define DBDMA_SIZE            (DBDMA_REGS * sizeof(uint32_t))

#define DBDMA_CHANNEL_SHIFT   7

#define DBDMA_CHANNEL_SIZE    (1 << DBDMA_CHANNEL_SHIFT)

#define DBDMA_CHANNELS        (0x1000 >> DBDMA_CHANNEL_SHIFT)

/* Bits in control and status registers */

#define RUN        0x8000

#define PAUSE        0x4000

#define FLUSH        0x2000

#define WAKE        0x1000

#define DEAD        0x0800

#define ACTIVE        0x0400

#define BT        0x0100

#define DEVSTAT        0x00ff

/*

 * DBDMA command structure.  These fields are all little-endian!

 */

typedef struct dbdma_cmd {

    uint16_t req_count;          /* requested byte transfer count */

    uint16_t command;          /* command word (has bit-fields) */

    uint32_t phy_addr;          /* physical data address */

    uint32_t cmd_dep;          /* command-dependent field */

    uint16_t res_count;          /* residual count after completion */

    uint16_t xfer_status; /* transfer status */

} dbdma_cmd;

/* DBDMA command values in command field */

#define COMMAND_MASK    0xf000

#define OUTPUT_MORE        0x0000        /* transfer memory data to stream */

#define OUTPUT_LAST        0x1000        /* ditto followed by end marker */

#define INPUT_MORE        0x2000        /* transfer stream data to memory */

#define INPUT_LAST        0x3000        /* ditto, expect end marker */

#define STORE_WORD        0x4000        /* write word (4 bytes) to device reg */

#define LOAD_WORD        0x5000        /* read word (4 bytes) from device reg */

#define DBDMA_NOP        0x6000        /* do nothing */

#define DBDMA_STOP        0x7000        /* suspend processing */

/* Key values in command field */

#define KEY_MASK        0x0700

#define KEY_STREAM0        0x0000        /* usual data stream */

#define KEY_STREAM1        0x0100        /* control/status stream */

#define KEY_STREAM2        0x0200        /* device-dependent stream */

#define KEY_STREAM3        0x0300        /* device-dependent stream */

#define KEY_STREAM4        0x0400        /* reserved */

#define KEY_REGS        0x0500        /* device register space */

#define KEY_SYSTEM        0x0600        /* system memory-mapped space */

#define KEY_DEVICE        0x0700        /* device memory-mapped space */

/* Interrupt control values in command field */

#define INTR_MASK       0x0030

#define INTR_NEVER        0x0000        /* don't interrupt */

#define INTR_IFSET        0x0010        /* intr if condition bit is 1 */

#define INTR_IFCLR        0x0020        /* intr if condition bit is 0 */

#define INTR_ALWAYS        0x0030        /* always interrupt */

/* Branch control values in command field */

#define BR_MASK         0x000c

#define BR_NEVER        0x0000        /* don't branch */

#define BR_IFSET        0x0004        /* branch if condition bit is 1 */

#define BR_IFCLR        0x0008        /* branch if condition bit is 0 */

#define BR_ALWAYS        0x000c        /* always branch */

/* Wait control values in command field */

#define WAIT_MASK       0x0003

#define WAIT_NEVER        0x0000        /* don't wait */

#define WAIT_IFSET        0x0001        /* wait if condition bit is 1 */

#define WAIT_IFCLR        0x0002        /* wait if condition bit is 0 */

#define WAIT_ALWAYS        0x0003        /* always wait */

typedef struct DBDMA_channel {

    int channel;

    uint32_t regs[DBDMA_REGS];

    qemu_irq irq;

    DBDMA_io io;

    DBDMA_rw rw;

    DBDMA_flush flush;

    dbdma_cmd current;

    int processing;

} DBDMA_channel;

typedef struct {

    MemoryRegion mem;

    DBDMA_channel channels[DBDMA_CHANNELS];

} DBDMAState;

#ifdef DEBUG_DBDMA

static void dump_dbdma_cmd(dbdma_cmd *cmd)

{

    printf("dbdma_cmd %p\n", cmd);

    printf("    req_count 0x%04x\n", le16_to_cpu(cmd->req_count));

    printf("    command 0x%04x\n", le16_to_cpu(cmd->command));

    printf("    phy_addr 0x%08x\n", le32_to_cpu(cmd->phy_addr));

    printf("    cmd_dep 0x%08x\n", le32_to_cpu(cmd->cmd_dep));

    printf("    res_count 0x%04x\n", le16_to_cpu(cmd->res_count));

    printf("    xfer_status 0x%04x\n", le16_to_cpu(cmd->xfer_status));

}

#else

static void dump_dbdma_cmd(dbdma_cmd *cmd)

{

}

#endif

static void dbdma_cmdptr_load(DBDMA_channel *ch)

{

    DBDMA_DPRINTF("dbdma_cmdptr_load 0x%08x\n",

                  ch->regs[DBDMA_CMDPTR_LO]);

    cpu_physical_memory_read(ch->regs[DBDMA_CMDPTR_LO],

                             (uint8_t*)&ch->current, sizeof(dbdma_cmd));

}

static void dbdma_cmdptr_save(DBDMA_channel *ch)

{

    DBDMA_DPRINTF("dbdma_cmdptr_save 0x%08x\n",

                  ch->regs[DBDMA_CMDPTR_LO]);

    DBDMA_DPRINTF("xfer_status 0x%08x res_count 0x%04x\n",

                  le16_to_cpu(ch->current.xfer_status),

                  le16_to_cpu(ch->current.res_count));

    cpu_physical_memory_write(ch->regs[DBDMA_CMDPTR_LO],

                              (uint8_t*)&ch->current, sizeof(dbdma_cmd));

}

static void kill_channel(DBDMA_channel *ch)

{

    DBDMA_DPRINTF("kill_channel\n");

    ch->regs[DBDMA_STATUS] |= DEAD;

    ch->regs[DBDMA_STATUS] &= ~ACTIVE;

    qemu_irq_raise(ch->irq);

}

static void conditional_interrupt(DBDMA_channel *ch)

{

    dbdma_cmd *current = &ch->current;

    uint16_t intr;

    uint16_t sel_mask, sel_value;

    uint32_t status;

    int cond;

    DBDMA_DPRINTF("conditional_interrupt\n");

    intr = le16_to_cpu(current->command) & INTR_MASK;

    switch(intr) {

    case INTR_NEVER:  /* don't interrupt */

        return;

    case INTR_ALWAYS: /* always interrupt */

        qemu_irq_raise(ch->irq);

        return;

    }

    status = ch->regs[DBDMA_STATUS] & DEVSTAT;

    sel_mask = (ch->regs[DBDMA_INTR_SEL] >> 16) & 0x0f;

    sel_value = ch->regs[DBDMA_INTR_SEL] & 0x0f;

    cond = (status & sel_mask) == (sel_value & sel_mask);

    switch(intr) {

    case INTR_IFSET:  /* intr if condition bit is 1 */

        if (cond)

            qemu_irq_raise(ch->irq);

        return;

    case INTR_IFCLR:  /* intr if condition bit is 0 */

        if (!cond)

            qemu_irq_raise(ch->irq);

        return;

    }

}

static int conditional_wait(DBDMA_channel *ch)

{

    dbdma_cmd *current = &ch->current;

    uint16_t wait;

    uint16_t sel_mask, sel_value;

    uint32_t status;

    int cond;

    DBDMA_DPRINTF("conditional_wait\n");

    wait = le16_to_cpu(current->command) & WAIT_MASK;

    switch(wait) {

    case WAIT_NEVER:  /* don't wait */

        return 0;

    case WAIT_ALWAYS: /* always wait */

        return 1;

    }

    status = ch->regs[DBDMA_STATUS] & DEVSTAT;

    sel_mask = (ch->regs[DBDMA_WAIT_SEL] >> 16) & 0x0f;

    sel_value = ch->regs[DBDMA_WAIT_SEL] & 0x0f;

    cond = (status & sel_mask) == (sel_value & sel_mask);

    switch(wait) {

    case WAIT_IFSET:  /* wait if condition bit is 1 */

        if (cond)

            return 1;

        return 0;

    case WAIT_IFCLR:  /* wait if condition bit is 0 */

        if (!cond)

            return 1;

        return 0;

    }

    return 0;

}

static void next(DBDMA_channel *ch)

{

    uint32_t cp;

    ch->regs[DBDMA_STATUS] &= ~BT;

    cp = ch->regs[DBDMA_CMDPTR_LO];

    ch->regs[DBDMA_CMDPTR_LO] = cp + sizeof(dbdma_cmd);

    dbdma_cmdptr_load(ch);

}

static void branch(DBDMA_channel *ch)

{

    dbdma_cmd *current = &ch->current;

    ch->regs[DBDMA_CMDPTR_LO] = current->cmd_dep;

    ch->regs[DBDMA_STATUS] |= BT;

    dbdma_cmdptr_load(ch);

}

static void conditional_branch(DBDMA_channel *ch)

{

    dbdma_cmd *current = &ch->current;

    uint16_t br;

    uint16_t sel_mask, sel_value;

    uint32_t status;

    int cond;

    DBDMA_DPRINTF("conditional_branch\n");

    /* check if we must branch */

    br = le16_to_cpu(current->command) & BR_MASK;

    switch(br) {

    case BR_NEVER:  /* don't branch */

        next(ch);

        return;

    case BR_ALWAYS: /* always branch */

        branch(ch);

        return;

    }

    status = ch->regs[DBDMA_STATUS] & DEVSTAT;

    sel_mask = (ch->regs[DBDMA_BRANCH_SEL] >> 16) & 0x0f;

    sel_value = ch->regs[DBDMA_BRANCH_SEL] & 0x0f;

    cond = (status & sel_mask) == (sel_value & sel_mask);

    switch(br) {

    case BR_IFSET:  /* branch if condition bit is 1 */

        if (cond)

            branch(ch);

        else

            next(ch);

        return;

    case BR_IFCLR:  /* branch if condition bit is 0 */

        if (!cond)

            branch(ch);

        else

            next(ch);

        return;

    }

}

static QEMUBH *dbdma_bh;

static void channel_run(DBDMA_channel *ch);

static void dbdma_end(DBDMA_io *io)

{

    DBDMA_channel *ch = io->channel;

    dbdma_cmd *current = &ch->current;

    if (conditional_wait(ch))

        goto wait;

    current->xfer_status = cpu_to_le16(ch->regs[DBDMA_STATUS]);

    current->res_count = cpu_to_le16(io->len);

    dbdma_cmdptr_save(ch);

    if (io->is_last)

        ch->regs[DBDMA_STATUS] &= ~FLUSH;

    conditional_interrupt(ch);

    conditional_branch(ch);

wait:

    ch->processing = 0;

    if ((ch->regs[DBDMA_STATUS] & RUN) &&

        (ch->regs[DBDMA_STATUS] & ACTIVE))

        channel_run(ch);

}

static void start_output(DBDMA_channel *ch, int key, uint32_t addr,

                        uint16_t req_count, int is_last)

{

    DBDMA_DPRINTF("start_output\n");

    /* KEY_REGS, KEY_DEVICE and KEY_STREAM

     * are not implemented in the mac-io chip

     */

    DBDMA_DPRINTF("addr 0x%x key 0x%x\n", addr, key);

    if (!addr || key > KEY_STREAM3) {

        kill_channel(ch);

        return;

    }

    ch->io.addr = addr;

    ch->io.len = req_count;

    ch->io.is_last = is_last;

    ch->io.dma_end = dbdma_end;

    ch->io.is_dma_out = 1;

    ch->processing = 1;

    if (ch->rw) {

        ch->rw(&ch->io);

    }

}

static void start_input(DBDMA_channel *ch, int key, uint32_t addr,

                       uint16_t req_count, int is_last)

{

    DBDMA_DPRINTF("start_input\n");

    /* KEY_REGS, KEY_DEVICE and KEY_STREAM

     * are not implemented in the mac-io chip

     */

    if (!addr || key > KEY_STREAM3) {

        kill_channel(ch);

        return;

    }

    ch->io.addr = addr;

    ch->io.len = req_count;

    ch->io.is_last = is_last;

    ch->io.dma_end = dbdma_end;

    ch->io.is_dma_out = 0;

    ch->processing = 1;

    if (ch->rw) {

        ch->rw(&ch->io);

    }

}

static void load_word(DBDMA_channel *ch, int key, uint32_t addr,

                     uint16_t len)

{

    dbdma_cmd *current = &ch->current;

    uint32_t val;

    DBDMA_DPRINTF("load_word\n");

    /* only implements KEY_SYSTEM */

    if (key != KEY_SYSTEM) {

        printf("DBDMA: LOAD_WORD, unimplemented key %x\n", key);

        kill_channel(ch);

        return;

    }

    cpu_physical_memory_read(addr, (uint8_t*)&val, len);

    if (len == 2)

        val = (val << 16) | (current->cmd_dep & 0x0000ffff);

    else if (len == 1)

        val = (val << 24) | (current->cmd_dep & 0x00ffffff);

    current->cmd_dep = val;

    if (conditional_wait(ch))

        goto wait;

    current->xfer_status = cpu_to_le16(ch->regs[DBDMA_STATUS]);

    dbdma_cmdptr_save(ch);

    ch->regs[DBDMA_STATUS] &= ~FLUSH;

    conditional_interrupt(ch);

    next(ch);

wait:

    qemu_bh_schedule(dbdma_bh);

}

static void store_word(DBDMA_channel *ch, int key, uint32_t addr,

                      uint16_t len)

{

    dbdma_cmd *current = &ch->current;

    uint32_t val;

    DBDMA_DPRINTF("store_word\n");

    /* only implements KEY_SYSTEM */

    if (key != KEY_SYSTEM) {

        printf("DBDMA: STORE_WORD, unimplemented key %x\n", key);

        kill_channel(ch);

        return;

    }

    val = current->cmd_dep;

    if (len == 2)

        val >>= 16;

    else if (len == 1)

        val >>= 24;

    cpu_physical_memory_write(addr, (uint8_t*)&val, len);

    if (conditional_wait(ch))

        goto wait;

    current->xfer_status = cpu_to_le16(ch->regs[DBDMA_STATUS]);

    dbdma_cmdptr_save(ch);

    ch->regs[DBDMA_STATUS] &= ~FLUSH;

    conditional_interrupt(ch);

    next(ch);

wait:

    qemu_bh_schedule(dbdma_bh);

}

static void nop(DBDMA_channel *ch)

{

    dbdma_cmd *current = &ch->current;

    if (conditional_wait(ch))

        goto wait;

    current->xfer_status = cpu_to_le16(ch->regs[DBDMA_STATUS]);

    dbdma_cmdptr_save(ch);

    conditional_interrupt(ch);

    conditional_branch(ch);

wait:

    qemu_bh_schedule(dbdma_bh);

}

static void stop(DBDMA_channel *ch)

{

    ch->regs[DBDMA_STATUS] &= ~(ACTIVE|DEAD|FLUSH);

    /* the stop command does not increment command pointer */

}

static void channel_run(DBDMA_channel *ch)

{

    dbdma_cmd *current = &ch->current;

    uint16_t cmd, key;

    uint16_t req_count;

    uint32_t phy_addr;

    DBDMA_DPRINTF("channel_run\n");

    dump_dbdma_cmd(current);

    /* clear WAKE flag at command fetch */

    ch->regs[DBDMA_STATUS] &= ~WAKE;

    cmd = le16_to_cpu(current->command) & COMMAND_MASK;

    switch (cmd) {

    case DBDMA_NOP:

        nop(ch);

        return;

    case DBDMA_STOP:

        stop(ch);

        return;

    }

    key = le16_to_cpu(current->command) & 0x0700;

    req_count = le16_to_cpu(current->req_count);

    phy_addr = le32_to_cpu(current->phy_addr);

    if (key == KEY_STREAM4) {

        printf("command %x, invalid key 4\n", cmd);

        kill_channel(ch);

        return;

    }

    switch (cmd) {

    case OUTPUT_MORE:

        start_output(ch, key, phy_addr, req_count, 0);

        return;

    case OUTPUT_LAST:

        start_output(ch, key, phy_addr, req_count, 1);

        return;

    case INPUT_MORE:

        start_input(ch, key, phy_addr, req_count, 0);

        return;

    case INPUT_LAST:

        start_input(ch, key, phy_addr, req_count, 1);

        return;

    }

    if (key < KEY_REGS) {

        printf("command %x, invalid key %x\n", cmd, key);

        key = KEY_SYSTEM;

    }

    /* for LOAD_WORD and STORE_WORD, req_count is on 3 bits

     * and BRANCH is invalid

     */

    req_count = req_count & 0x0007;

    if (req_count & 0x4) {

        req_count = 4;

        phy_addr &= ~3;

    } else if (req_count & 0x2) {

        req_count = 2;

        phy_addr &= ~1;

    } else

        req_count = 1;

    switch (cmd) {

    case LOAD_WORD:

        load_word(ch, key, phy_addr, req_count);

        return;

    case STORE_WORD:

        store_word(ch, key, phy_addr, req_count);

        return;

    }

}

static void DBDMA_run(DBDMAState *s)

{

    int channel;

    for (channel = 0; channel < DBDMA_CHANNELS; channel++) {

        DBDMA_channel *ch = &s->channels[channel];

        uint32_t status = ch->regs[DBDMA_STATUS];

        if (!ch->processing && (status & RUN) && (status & ACTIVE)) {

            channel_run(ch);

        }

    }

}

static void DBDMA_run_bh(void *opaque)

{

    DBDMAState *s = opaque;

    DBDMA_DPRINTF("DBDMA_run_bh\n");

    DBDMA_run(s);

}

void DBDMA_register_channel(void *dbdma, int nchan, qemu_irq irq,

                            DBDMA_rw rw, DBDMA_flush flush,

                            void *opaque)

{

    DBDMAState *s = dbdma;

    DBDMA_channel *ch = &s->channels[nchan];

    DBDMA_DPRINTF("DBDMA_register_channel 0x%x\n", nchan);

    ch->irq = irq;

    ch->channel = nchan;

    ch->rw = rw;

    ch->flush = flush;

    ch->io.opaque = opaque;

    ch->io.channel = ch;

}

void DBDMA_schedule(void)

{

    qemu_notify_event();

}

static void

dbdma_control_write(DBDMA_channel *ch)

{

    uint16_t mask, value;

    uint32_t status;

    mask = (ch->regs[DBDMA_CONTROL] >> 16) & 0xffff;

    value = ch->regs[DBDMA_CONTROL] & 0xffff;

    value &= (RUN | PAUSE | FLUSH | WAKE | DEVSTAT);

    status = ch->regs[DBDMA_STATUS];

    status = (value & mask) | (status & ~mask);

    if (status & WAKE)

        status |= ACTIVE;

    if (status & RUN) {

        status |= ACTIVE;

        status &= ~DEAD;

    }

    if (status & PAUSE)

        status &= ~ACTIVE;

    if ((ch->regs[DBDMA_STATUS] & RUN) && !(status & RUN)) {

        /* RUN is cleared */

        status &= ~(ACTIVE|DEAD);

    }

    DBDMA_DPRINTF("    status 0x%08x\n", status);

    ch->regs[DBDMA_STATUS] = status;

    if (status & ACTIVE)

        qemu_bh_schedule(dbdma_bh);

    if ((status & FLUSH) && ch->flush)

        ch->flush(&ch->io);

}

static void dbdma_write(void *opaque, target_phys_addr_t addr,

                        uint64_t value, unsigned size)

{

    int channel = addr >> DBDMA_CHANNEL_SHIFT;

    DBDMAState *s = opaque;

    DBDMA_channel *ch = &s->channels[channel];

    int reg = (addr - (channel << DBDMA_CHANNEL_SHIFT)) >> 2;

    DBDMA_DPRINTF("writel 0x" TARGET_FMT_plx " <= 0x%08x\n", addr, value);

    DBDMA_DPRINTF("channel 0x%x reg 0x%x\n",

                  (uint32_t)addr >> DBDMA_CHANNEL_SHIFT, reg);

    /* cmdptr cannot be modified if channel is RUN or ACTIVE */

    if (reg == DBDMA_CMDPTR_LO &&

        (ch->regs[DBDMA_STATUS] & (RUN | ACTIVE)))

        return;

    ch->regs[reg] = value;

    switch(reg) {

    case DBDMA_CONTROL:

        dbdma_control_write(ch);

        break;

    case DBDMA_CMDPTR_LO:

        /* 16-byte aligned */

        ch->regs[DBDMA_CMDPTR_LO] &= ~0xf;

        dbdma_cmdptr_load(ch);

        break;

    case DBDMA_STATUS:

    case DBDMA_INTR_SEL:

    case DBDMA_BRANCH_SEL:

    case DBDMA_WAIT_SEL:

        /* nothing to do */

        break;

    case DBDMA_XFER_MODE:

    case DBDMA_CMDPTR_HI:

    case DBDMA_DATA2PTR_HI:

    case DBDMA_DATA2PTR_LO:

    case DBDMA_ADDRESS_HI:

    case DBDMA_BRANCH_ADDR_HI:

    case DBDMA_RES1:

    case DBDMA_RES2:

    case DBDMA_RES3:

    case DBDMA_RES4:

        /* unused */

        break;

    }

}

static uint64_t dbdma_read(void *opaque, target_phys_addr_t addr,

                           unsigned size)

{

    uint32_t value;

    int channel = addr >> DBDMA_CHANNEL_SHIFT;

    DBDMAState *s = opaque;

    DBDMA_channel *ch = &s->channels[channel];

    int reg = (addr - (channel << DBDMA_CHANNEL_SHIFT)) >> 2;

    value = ch->regs[reg];

    DBDMA_DPRINTF("readl 0x" TARGET_FMT_plx " => 0x%08x\n", addr, value);

    DBDMA_DPRINTF("channel 0x%x reg 0x%x\n",

                  (uint32_t)addr >> DBDMA_CHANNEL_SHIFT, reg);

    switch(reg) {

    case DBDMA_CONTROL:

        value = 0;

        break;

    case DBDMA_STATUS:

    case DBDMA_CMDPTR_LO:

    case DBDMA_INTR_SEL:

    case DBDMA_BRANCH_SEL:

    case DBDMA_WAIT_SEL:

        /* nothing to do */

        break;

    case DBDMA_XFER_MODE:

    case DBDMA_CMDPTR_HI:

    case DBDMA_DATA2PTR_HI:

    case DBDMA_DATA2PTR_LO:

    case DBDMA_ADDRESS_HI:

    case DBDMA_BRANCH_ADDR_HI:

        /* unused */

        value = 0;

        break;

    case DBDMA_RES1:

    case DBDMA_RES2:

    case DBDMA_RES3:

    case DBDMA_RES4:

        /* reserved */

        break;

    }

    return value;

}

static const MemoryRegionOps dbdma_ops = {

    .read = dbdma_read,

    .write = dbdma_write,

    .endianness = DEVICE_LITTLE_ENDIAN,

    .valid = {

        .min_access_size = 4,

        .max_access_size = 4,

    },

};

static const VMStateDescription vmstate_dbdma_channel = {

    .name = "dbdma_channel",

    .version_id = 0,

    .minimum_version_id = 0,

    .minimum_version_id_old = 0,

    .fields      = (VMStateField[]) {

        VMSTATE_UINT32_ARRAY(regs, struct DBDMA_channel, DBDMA_REGS),

        VMSTATE_END_OF_LIST()

    }

};

static const VMStateDescription vmstate_dbdma = {

    .name = "dbdma",

    .version_id = 2,

    .minimum_version_id = 2,

    .minimum_version_id_old = 2,

    .fields      = (VMStateField[]) {

        VMSTATE_STRUCT_ARRAY(channels, DBDMAState, DBDMA_CHANNELS, 1,

                             vmstate_dbdma_channel, DBDMA_channel),

        VMSTATE_END_OF_LIST()

    }

};

static void dbdma_reset(void *opaque)

{

    DBDMAState *s = opaque;

    int i;

    for (i = 0; i < DBDMA_CHANNELS; i++)

        memset(s->channels[i].regs, 0, DBDMA_SIZE);

}

void* DBDMA_init (MemoryRegion **dbdma_mem)

{

    DBDMAState *s;

    s = g_malloc0(sizeof(DBDMAState));

    memory_region_init_io(&s->mem, &dbdma_ops, s, "dbdma", 0x1000);

    *dbdma_mem = &s->mem;

    vmstate_register(NULL, -1, &vmstate_dbdma, s);

    qemu_register_reset(dbdma_reset, s);

    dbdma_bh = qemu_bh_new(DBDMA_run_bh, s);

    return s;

}