GPIO I2C rework

Reqrite bitbanging I2C implementation.  New code improves stop/start
condition handling, and gives more accurate input line level.

Introduce intermediate abstraction layer for I2C bitbanging that
is not connected via a GPIO port.

Signed-off-by: Paul Brook <paul@codesourcery.com>

3 files changed, 161 insertions, 100 deletions

diff --git a/hw/bitbang_i2c.c b/hw/bitbang_i2c.c
index 443ddb2..4ee99a1 100644
--- a/hw/bitbang_i2c.c
+++ b/hw/bitbang_i2c.c
@@ -7,12 +7,20 @@
  * This code is licenced under the GNU GPL v2.
  */
 #include "hw.h"
-#include "i2c.h"
+#include "bitbang_i2c.h"
 #include "sysbus.h"
 
+//#define DEBUG_BITBANG_I2C
+
+#ifdef DEBUG_BITBANG_I2C
+#define DPRINTF(fmt, ...) \
+do { printf("bitbang_i2c: " fmt , ## __VA_ARGS__); } while (0)
+#else
+#define DPRINTF(fmt, ...) do {} while(0)
+#endif
+
 typedef enum bitbang_i2c_state {
     STOPPED = 0,
-    INITIALIZING,
     SENDING_BIT7,
     SENDING_BIT6,
     SENDING_BIT5,
@@ -33,138 +41,171 @@ typedef enum bitbang_i2c_state {
     SENDING_ACK
 } bitbang_i2c_state;
 
-typedef struct bitbang_i2c_interface {
-    SysBusDevice busdev;
+struct bitbang_i2c_interface {
     i2c_bus *bus;
     bitbang_i2c_state state;
     int last_data;
     int last_clock;
+    int device_out;
     uint8_t buffer;
     int current_addr;
-    qemu_irq out;
-} bitbang_i2c_interface;
+};
 
 static void bitbang_i2c_enter_stop(bitbang_i2c_interface *i2c)
 {
+    DPRINTF("STOP\n");
     if (i2c->current_addr >= 0)
         i2c_end_transfer(i2c->bus);
     i2c->current_addr = -1;
     i2c->state = STOPPED;
 }
 
-static void bitbang_i2c_gpio_set(void *opaque, int irq, int level)
+/* Set device data pin.  */
+static int bitbang_i2c_ret(bitbang_i2c_interface *i2c, int level)
+{
+    i2c->device_out = level;
+    //DPRINTF("%d %d %d\n", i2c->last_clock, i2c->last_data, i2c->device_out);
+    return level & i2c->last_data;
+}
+
+/* Leave device data pin unodified.  */
+static int bitbang_i2c_nop(bitbang_i2c_interface *i2c)
+{
+    return bitbang_i2c_ret(i2c, i2c->device_out);
+}
+
+/* Returns data line level.  */
+int bitbang_i2c_set(bitbang_i2c_interface *i2c, int line, int level)
 {
-    bitbang_i2c_interface *i2c = opaque;
     int data;
-    int clock;
-    int data_goes_up;
-    int data_goes_down;
-    int clock_goes_up;
-    int clock_goes_down;
-
-    /* get pins states */
-    data    = i2c->last_data;
-    clock   = i2c->last_clock;
-
-    if (irq == 0)
-        data = level;
-    if (irq == 1)
-        clock = level;
-
-    /* compute pins changes */
-    data_goes_up    = data == 1 && i2c->last_data == 0;
-    data_goes_down  = data == 0 && i2c->last_data == 1;
-    clock_goes_up   = clock == 1 && i2c->last_clock == 0;
-    clock_goes_down = clock == 0 && i2c->last_clock == 1;
-
-    if (data_goes_up == 0 && data_goes_down == 0 &&
-        clock_goes_up == 0 && clock_goes_down == 0)
-        return;
-
-    if (!i2c)
-        return;
-
-    if ((RECEIVING_BIT7 > i2c->state && i2c->state > RECEIVING_BIT0)
-            || i2c->state == WAITING_FOR_ACK)
-        qemu_set_irq(i2c->out, 0);
 
-    switch (i2c->state) {
-    case STOPPED:
-        if (data_goes_down && clock == 1)
-            i2c->state = INITIALIZING;
-        break;
+    if (level != 0 && level != 1) {
+        abort();
+    }
 
-    case INITIALIZING:
-        if (clock_goes_down && data == 0)
+    if (line == BITBANG_I2C_SDA) {
+        if (level == i2c->last_data) {
+            return bitbang_i2c_nop(i2c);
+        }
+        i2c->last_data = level;
+        if (i2c->last_clock == 0) {
+            return bitbang_i2c_nop(i2c);
+        }
+        if (level == 0) {
+            DPRINTF("START\n");
+            /* START condition.  */
             i2c->state = SENDING_BIT7;
-        else
+            i2c->current_addr = -1;
+        } else {
+            /* STOP condition.  */
             bitbang_i2c_enter_stop(i2c);
-        break;
+        }
+        return bitbang_i2c_ret(i2c, 1);
+    }
+
+    data = i2c->last_data;
+    if (i2c->last_clock == level) {
+        return bitbang_i2c_nop(i2c);
+    }
+    i2c->last_clock = level;
+    if (level == 0) {
+        /* State is set/read at the start of the clock pulse.
+           release the data line at the end.  */
+        return bitbang_i2c_ret(i2c, 1);
+    }
+    switch (i2c->state) {
+    case STOPPED:
+        return bitbang_i2c_ret(i2c, 1);
 
     case SENDING_BIT7 ... SENDING_BIT0:
-        if (clock_goes_down) {
-            i2c->buffer = (i2c->buffer << 1) | data;
-            /* will end up in WAITING_FOR_ACK */
-            i2c->state++; 
-        } else if (data_goes_up && clock == 1)
-            bitbang_i2c_enter_stop(i2c);
-        break;
+        i2c->buffer = (i2c->buffer << 1) | data;
+        /* will end up in WAITING_FOR_ACK */
+        i2c->state++; 
+        return bitbang_i2c_ret(i2c, 1);
 
     case WAITING_FOR_ACK:
-        if (clock_goes_down) {
-            if (i2c->current_addr < 0) {
-                i2c->current_addr = i2c->buffer;
-                i2c_start_transfer(i2c->bus, (i2c->current_addr & 0xfe) / 2,
-                                   i2c->buffer & 1);
-            } else
-                i2c_send(i2c->bus, i2c->buffer);
-            if (i2c->current_addr & 1) {
-                i2c->state = RECEIVING_BIT7;
-                i2c->buffer = i2c_recv(i2c->bus);
-            } else
-                i2c->state = SENDING_BIT7;
-        } else if (data_goes_up && clock == 1)
-            bitbang_i2c_enter_stop(i2c);
-        break;
-
-    case RECEIVING_BIT7 ... RECEIVING_BIT0:
-        qemu_set_irq(i2c->out, i2c->buffer >> 7);
-        if (clock_goes_down) {
-            /* will end up in SENDING_ACK */
-            i2c->state++;
-            i2c->buffer <<= 1;
-        } else if (data_goes_up && clock == 1)
-            bitbang_i2c_enter_stop(i2c);
-        break;
+        if (i2c->current_addr < 0) {
+            i2c->current_addr = i2c->buffer;
+            DPRINTF("Address 0x%02x\n", i2c->current_addr);
+            i2c_start_transfer(i2c->bus, i2c->current_addr >> 1,
+                               i2c->current_addr & 1);
+        } else {
+            DPRINTF("Sent 0x%02x\n", i2c->buffer);
+            i2c_send(i2c->bus, i2c->buffer);
+        }
+        if (i2c->current_addr & 1) {
+            i2c->state = RECEIVING_BIT7;
+        } else {
+            i2c->state = SENDING_BIT7;
+        }
+        return bitbang_i2c_ret(i2c, 0);
+
+    case RECEIVING_BIT7:
+        i2c->buffer = i2c_recv(i2c->bus);
+        DPRINTF("RX byte 0x%02x\n", i2c->buffer);
+        /* Fall through... */
+    case RECEIVING_BIT6 ... RECEIVING_BIT0:
+        data = i2c->buffer >> 7;
+        /* will end up in SENDING_ACK */
+        i2c->state++;
+        i2c->buffer <<= 1;
+        return bitbang_i2c_ret(i2c, data);
 
     case SENDING_ACK:
-        if (clock_goes_down) {
-            i2c->state = RECEIVING_BIT7;
-            if (data == 0)
-                i2c->buffer = i2c_recv(i2c->bus);
-            else
-                i2c_nack(i2c->bus);
-        } else if (data_goes_up && clock == 1)
-            bitbang_i2c_enter_stop(i2c);
-        break;
+        i2c->state = RECEIVING_BIT7;
+        if (data != 0) {
+            DPRINTF("NACKED\n");
+            i2c_nack(i2c->bus);
+        } else {
+            DPRINTF("ACKED\n");
+        }
+        return bitbang_i2c_ret(i2c, 1);
     }
+    abort();
+}
+
+bitbang_i2c_interface *bitbang_i2c_init(i2c_bus *bus)
+{
+    bitbang_i2c_interface *s;
+
+    s = qemu_mallocz(sizeof(bitbang_i2c_interface));
+
+    s->bus = bus;
+    s->last_data = 1;
+    s->last_clock = 1;
+    s->device_out = 1;
+
+    return s;
+}
 
-    i2c->last_data = data;
-    i2c->last_clock = clock;
+/* GPIO interface.  */
+typedef struct {
+    SysBusDevice busdev;
+    bitbang_i2c_interface *bitbang;
+    int last_level;
+    qemu_irq out;
+} GPIOI2CState;
+
+static void bitbang_i2c_gpio_set(void *opaque, int irq, int level)
+{
+    GPIOI2CState *s = opaque;
+
+    level = bitbang_i2c_set(s->bitbang, irq, level);
+    if (level != s->last_level) {
+        s->last_level = level;
+        qemu_set_irq(s->out, level);
+    }
 }
 
-static int bitbang_i2c_init(SysBusDevice *dev)
+static int gpio_i2c_init(SysBusDevice *dev)
 {
-    bitbang_i2c_interface *s = FROM_SYSBUS(bitbang_i2c_interface, dev);
+    GPIOI2CState *s = FROM_SYSBUS(GPIOI2CState, dev);
     i2c_bus *bus;
 
     sysbus_init_mmio(dev, 0x0, 0);
 
     bus = i2c_init_bus(&dev->qdev, "i2c");
-    s->bus = bus;
-
-    s->last_data = 1;
-    s->last_clock = 1;
+    s->bitbang = bitbang_i2c_init(bus);
 
     qdev_init_gpio_in(&dev->qdev, bitbang_i2c_gpio_set, 2);
     qdev_init_gpio_out(&dev->qdev, &s->out, 1);
@@ -172,10 +213,16 @@ static int bitbang_i2c_init(SysBusDevice *dev)
     return 0;
 }
 
+static SysBusDeviceInfo gpio_i2c_info = {
+    .init = gpio_i2c_init,
+    .qdev.name  = "gpio_i2c",
+    .qdev.desc  = "Virtual GPIO to I2C bridge",
+    .qdev.size  = sizeof(GPIOI2CState),
+};
+
 static void bitbang_i2c_register(void)
 {
-    sysbus_register_dev("bitbang_i2c",
-        sizeof(bitbang_i2c_interface), bitbang_i2c_init);
+    sysbus_register_withprop(&gpio_i2c_info);
 }
 
 device_init(bitbang_i2c_register)
diff --git a/hw/bitbang_i2c.h b/hw/bitbang_i2c.h
new file mode 100644
index 0000000..519d2dc
--- /dev/null
+++ b/hw/bitbang_i2c.h
@@ -0,0 +1,14 @@
+#ifndef BITBANG_I2C_H
+#define BITBANG_I2C_H
+
+#include "i2c.h"
+
+typedef struct bitbang_i2c_interface bitbang_i2c_interface;
+
+#define BITBANG_I2C_SDA 0
+#define BITBANG_I2C_SCL 1
+
+bitbang_i2c_interface *bitbang_i2c_init(i2c_bus *bus);
+int bitbang_i2c_set(bitbang_i2c_interface *i2c, int line, int level);
+
+#endif
diff --git a/hw/musicpal.c b/hw/musicpal.c
index 0d21f17..264669f 100644
--- a/hw/musicpal.c
+++ b/hw/musicpal.c
@@ -1565,7 +1565,7 @@ static void musicpal_init(ram_addr_t ram_size,
     musicpal_misc_init();
 
     dev = sysbus_create_simple("musicpal_gpio", MP_GPIO_BASE, pic[MP_GPIO_IRQ]);
-    i2c_dev = sysbus_create_simple("bitbang_i2c", 0, NULL);
+    i2c_dev = sysbus_create_simple("gpio_i2c", 0, NULL);
     i2c = (i2c_bus *)qdev_get_child_bus(i2c_dev, "i2c");
 
     lcd_dev = sysbus_create_simple("musicpal_lcd", MP_LCD_BASE, NULL);