hw/bitbang_i2c.c

   1 /*
   2  * Bit-Bang i2c emulation extracted from
   3  * Marvell MV88W8618 / Freecom MusicPal emulation.
   4  *
   5  * Copyright (c) 2008 Jan Kiszka
   6  *
   7  * This code is licensed under the GNU GPL v2.
   8  */
   9 #include "hw.h"
  10 #include "bitbang_i2c.h"
  11 #include "sysbus.h"
  12
  13 //#define DEBUG_BITBANG_I2C
  14
  15 #ifdef DEBUG_BITBANG_I2C
  16 #define DPRINTF(fmt, ...) \
  17 do { printf("bitbang_i2c: " fmt , ## __VA_ARGS__); } while (0)
  18 #else
  19 #define DPRINTF(fmt, ...) do {} while(0)
  20 #endif
  21
  22 typedef enum bitbang_i2c_state {
  23     STOPPED = 0,
  24     SENDING_BIT7,
  25     SENDING_BIT6,
  26     SENDING_BIT5,
  27     SENDING_BIT4,
  28     SENDING_BIT3,
  29     SENDING_BIT2,
  30     SENDING_BIT1,
  31     SENDING_BIT0,
  32     WAITING_FOR_ACK,
  33     RECEIVING_BIT7,
  34     RECEIVING_BIT6,
  35     RECEIVING_BIT5,
  36     RECEIVING_BIT4,
  37     RECEIVING_BIT3,
  38     RECEIVING_BIT2,
  39     RECEIVING_BIT1,
  40     RECEIVING_BIT0,
  41     SENDING_ACK,
  42     SENT_NACK
  43 } bitbang_i2c_state;
  44
  45 struct bitbang_i2c_interface {
  46     i2c_bus *bus;
  47     bitbang_i2c_state state;
  48     int last_data;
  49     int last_clock;
  50     int device_out;
  51     uint8_t buffer;
  52     int current_addr;
  53 };
  54
  55 static void bitbang_i2c_enter_stop(bitbang_i2c_interface *i2c)
  56 {
  57     DPRINTF("STOP\n");
  58     if (i2c->current_addr >= 0)
  59         i2c_end_transfer(i2c->bus);
  60     i2c->current_addr = -1;
  61     i2c->state = STOPPED;
  62 }
  63
  64 /* Set device data pin.  */
  65 static int bitbang_i2c_ret(bitbang_i2c_interface *i2c, int level)
  66 {
  67     i2c->device_out = level;
  68     //DPRINTF("%d %d %d\n", i2c->last_clock, i2c->last_data, i2c->device_out);
  69     return level & i2c->last_data;
  70 }
  71
  72 /* Leave device data pin unodified.  */
  73 static int bitbang_i2c_nop(bitbang_i2c_interface *i2c)
  74 {
  75     return bitbang_i2c_ret(i2c, i2c->device_out);
  76 }
  77
  78 /* Returns data line level.  */
  79 int bitbang_i2c_set(bitbang_i2c_interface *i2c, int line, int level)
  80 {
  81     int data;
  82
  83     if (level != 0 && level != 1) {
  84         abort();
  85     }
  86
  87     if (line == BITBANG_I2C_SDA) {
  88         if (level == i2c->last_data) {
  89             return bitbang_i2c_nop(i2c);
  90         }
  91         i2c->last_data = level;
  92         if (i2c->last_clock == 0) {
  93             return bitbang_i2c_nop(i2c);
  94         }
  95         if (level == 0) {
  96             DPRINTF("START\n");
  97             /* START condition.  */
  98             i2c->state = SENDING_BIT7;
  99             i2c->current_addr = -1;
 100         } else {
 101             /* STOP condition.  */
 102             bitbang_i2c_enter_stop(i2c);
 103         }
 104         return bitbang_i2c_ret(i2c, 1);
 105     }
 106
 107     data = i2c->last_data;
 108     if (i2c->last_clock == level) {
 109         return bitbang_i2c_nop(i2c);
 110     }
 111     i2c->last_clock = level;
 112     if (level == 0) {
 113         /* State is set/read at the start of the clock pulse.
 114            release the data line at the end.  */
 115         return bitbang_i2c_ret(i2c, 1);
 116     }
 117     switch (i2c->state) {
 118     case STOPPED:
 119     case SENT_NACK:
 120         return bitbang_i2c_ret(i2c, 1);
 121
 122     case SENDING_BIT7 ... SENDING_BIT0:
 123         i2c->buffer = (i2c->buffer << 1) | data;
 124         /* will end up in WAITING_FOR_ACK */
 125         i2c->state++;
 126         return bitbang_i2c_ret(i2c, 1);
 127
 128     case WAITING_FOR_ACK:
 129         if (i2c->current_addr < 0) {
 130             i2c->current_addr = i2c->buffer;
 131             DPRINTF("Address 0x%02x\n", i2c->current_addr);
 132             i2c_start_transfer(i2c->bus, i2c->current_addr >> 1,
 133                                i2c->current_addr & 1);
 134         } else {
 135             DPRINTF("Sent 0x%02x\n", i2c->buffer);
 136             i2c_send(i2c->bus, i2c->buffer);
 137         }
 138         if (i2c->current_addr & 1) {
 139             i2c->state = RECEIVING_BIT7;
 140         } else {
 141             i2c->state = SENDING_BIT7;
 142         }
 143         return bitbang_i2c_ret(i2c, 0);
 144
 145     case RECEIVING_BIT7:
 146         i2c->buffer = i2c_recv(i2c->bus);
 147         DPRINTF("RX byte 0x%02x\n", i2c->buffer);
 148         /* Fall through... */
 149     case RECEIVING_BIT6 ... RECEIVING_BIT0:
 150         data = i2c->buffer >> 7;
 151         /* will end up in SENDING_ACK */
 152         i2c->state++;
 153         i2c->buffer <<= 1;
 154         return bitbang_i2c_ret(i2c, data);
 155
 156     case SENDING_ACK:
 157         i2c->state = RECEIVING_BIT7;
 158         if (data != 0) {
 159             DPRINTF("NACKED\n");
 160             i2c->state = SENT_NACK;
 161             i2c_nack(i2c->bus);
 162         } else {
 163             DPRINTF("ACKED\n");
 164         }
 165         return bitbang_i2c_ret(i2c, 1);
 166     }
 167     abort();
 168 }
 169
 170 bitbang_i2c_interface *bitbang_i2c_init(i2c_bus *bus)
 171 {
 172     bitbang_i2c_interface *s;
 173
 174     s = qemu_mallocz(sizeof(bitbang_i2c_interface));
 175
 176     s->bus = bus;
 177     s->last_data = 1;
 178     s->last_clock = 1;
 179     s->device_out = 1;
 180
 181     return s;
 182 }
 183
 184 /* GPIO interface.  */
 185 typedef struct {
 186     SysBusDevice busdev;
 187     bitbang_i2c_interface *bitbang;
 188     int last_level;
 189     qemu_irq out;
 190 } GPIOI2CState;
 191
 192 static void bitbang_i2c_gpio_set(void *opaque, int irq, int level)
 193 {
 194     GPIOI2CState *s = opaque;
 195
 196     level = bitbang_i2c_set(s->bitbang, irq, level);
 197     if (level != s->last_level) {
 198         s->last_level = level;
 199         qemu_set_irq(s->out, level);
 200     }
 201 }
 202
 203 static int gpio_i2c_init(SysBusDevice *dev)
 204 {
 205     GPIOI2CState *s = FROM_SYSBUS(GPIOI2CState, dev);
 206     i2c_bus *bus;
 207
 208     sysbus_init_mmio(dev, 0x0, 0);
 209
 210     bus = i2c_init_bus(&dev->qdev, "i2c");
 211     s->bitbang = bitbang_i2c_init(bus);
 212
 213     qdev_init_gpio_in(&dev->qdev, bitbang_i2c_gpio_set, 2);
 214     qdev_init_gpio_out(&dev->qdev, &s->out, 1);
 215
 216     return 0;
 217 }
 218
 219 static SysBusDeviceInfo gpio_i2c_info = {
 220     .init = gpio_i2c_init,
 221     .qdev.name  = "gpio_i2c",
 222     .qdev.desc  = "Virtual GPIO to I2C bridge",
 223     .qdev.size  = sizeof(GPIOI2CState),
 224 };
 225
 226 static void bitbang_i2c_register(void)
 227 {
 228     sysbus_register_withprop(&gpio_i2c_info);
 229 }
 230
 231 device_init(bitbang_i2c_register)