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 licenced under the GNU GPL v2.
   8  */
   9 #include "hw.h"
  10 #include "i2c.h"
  11 #include "sysbus.h"
  12
  13 typedef enum bitbang_i2c_state {
  14     STOPPED = 0,
  15     INITIALIZING,
  16     SENDING_BIT7,
  17     SENDING_BIT6,
  18     SENDING_BIT5,
  19     SENDING_BIT4,
  20     SENDING_BIT3,
  21     SENDING_BIT2,
  22     SENDING_BIT1,
  23     SENDING_BIT0,
  24     WAITING_FOR_ACK,
  25     RECEIVING_BIT7,
  26     RECEIVING_BIT6,
  27     RECEIVING_BIT5,
  28     RECEIVING_BIT4,
  29     RECEIVING_BIT3,
  30     RECEIVING_BIT2,
  31     RECEIVING_BIT1,
  32     RECEIVING_BIT0,
  33     SENDING_ACK
  34 } bitbang_i2c_state;
  35
  36 typedef struct bitbang_i2c_interface {
  37     SysBusDevice busdev;
  38     i2c_bus *bus;
  39     bitbang_i2c_state state;
  40     int last_data;
  41     int last_clock;
  42     uint8_t buffer;
  43     int current_addr;
  44     qemu_irq out;
  45 } bitbang_i2c_interface;
  46
  47 static void bitbang_i2c_enter_stop(bitbang_i2c_interface *i2c)
  48 {
  49     if (i2c->current_addr >= 0)
  50         i2c_end_transfer(i2c->bus);
  51     i2c->current_addr = -1;
  52     i2c->state = STOPPED;
  53 }
  54
  55 static void bitbang_i2c_gpio_set(void *opaque, int irq, int level)
  56 {
  57     bitbang_i2c_interface *i2c = opaque;
  58     int data;
  59     int clock;
  60     int data_goes_up;
  61     int data_goes_down;
  62     int clock_goes_up;
  63     int clock_goes_down;
  64
  65     /* get pins states */
  66     data    = i2c->last_data;
  67     clock   = i2c->last_clock;
  68
  69     if (irq == 0)
  70         data = level;
  71     if (irq == 1)
  72         clock = level;
  73
  74     /* compute pins changes */
  75     data_goes_up    = data == 1 && i2c->last_data == 0;
  76     data_goes_down  = data == 0 && i2c->last_data == 1;
  77     clock_goes_up   = clock == 1 && i2c->last_clock == 0;
  78     clock_goes_down = clock == 0 && i2c->last_clock == 1;
  79
  80     if (data_goes_up == 0 && data_goes_down == 0 &&
  81         clock_goes_up == 0 && clock_goes_down == 0)
  82         return;
  83
  84     if (!i2c)
  85         return;
  86
  87     if ((RECEIVING_BIT7 > i2c->state && i2c->state > RECEIVING_BIT0)
  88             || i2c->state == WAITING_FOR_ACK)
  89         qemu_set_irq(i2c->out, 0);
  90
  91     switch (i2c->state) {
  92     case STOPPED:
  93         if (data_goes_down && clock == 1)
  94             i2c->state = INITIALIZING;
  95         break;
  96
  97     case INITIALIZING:
  98         if (clock_goes_down && data == 0)
  99             i2c->state = SENDING_BIT7;
 100         else
 101             bitbang_i2c_enter_stop(i2c);
 102         break;
 103
 104     case SENDING_BIT7 ... SENDING_BIT0:
 105         if (clock_goes_down) {
 106             i2c->buffer = (i2c->buffer << 1) | data;
 107             /* will end up in WAITING_FOR_ACK */
 108             i2c->state++;
 109         } else if (data_goes_up && clock == 1)
 110             bitbang_i2c_enter_stop(i2c);
 111         break;
 112
 113     case WAITING_FOR_ACK:
 114         if (clock_goes_down) {
 115             if (i2c->current_addr < 0) {
 116                 i2c->current_addr = i2c->buffer;
 117                 i2c_start_transfer(i2c->bus, (i2c->current_addr & 0xfe) / 2,
 118                                    i2c->buffer & 1);
 119             } else
 120                 i2c_send(i2c->bus, i2c->buffer);
 121             if (i2c->current_addr & 1) {
 122                 i2c->state = RECEIVING_BIT7;
 123                 i2c->buffer = i2c_recv(i2c->bus);
 124             } else
 125                 i2c->state = SENDING_BIT7;
 126         } else if (data_goes_up && clock == 1)
 127             bitbang_i2c_enter_stop(i2c);
 128         break;
 129
 130     case RECEIVING_BIT7 ... RECEIVING_BIT0:
 131         qemu_set_irq(i2c->out, i2c->buffer >> 7);
 132         if (clock_goes_down) {
 133             /* will end up in SENDING_ACK */
 134             i2c->state++;
 135             i2c->buffer <<= 1;
 136         } else if (data_goes_up && clock == 1)
 137             bitbang_i2c_enter_stop(i2c);
 138         break;
 139
 140     case SENDING_ACK:
 141         if (clock_goes_down) {
 142             i2c->state = RECEIVING_BIT7;
 143             if (data == 0)
 144                 i2c->buffer = i2c_recv(i2c->bus);
 145             else
 146                 i2c_nack(i2c->bus);
 147         } else if (data_goes_up && clock == 1)
 148             bitbang_i2c_enter_stop(i2c);
 149         break;
 150     }
 151
 152     i2c->last_data = data;
 153     i2c->last_clock = clock;
 154 }
 155
 156 static int bitbang_i2c_init(SysBusDevice *dev)
 157 {
 158     bitbang_i2c_interface *s = FROM_SYSBUS(bitbang_i2c_interface, dev);
 159     i2c_bus *bus;
 160
 161     sysbus_init_mmio(dev, 0x0, 0);
 162
 163     bus = i2c_init_bus(&dev->qdev, "i2c");
 164     s->bus = bus;
 165
 166     s->last_data = 1;
 167     s->last_clock = 1;
 168
 169     qdev_init_gpio_in(&dev->qdev, bitbang_i2c_gpio_set, 2);
 170     qdev_init_gpio_out(&dev->qdev, &s->out, 1);
 171
 172     return 0;
 173 }
 174
 175 static void bitbang_i2c_register(void)
 176 {
 177     sysbus_register_dev("bitbang_i2c",
 178         sizeof(bitbang_i2c_interface), bitbang_i2c_init);
 179 }
 180
 181 device_init(bitbang_i2c_register)