repeated start

Author: ArcaneNibble

main.c

@@ -3,6 +3,9 @@
 #include "am1808.h"
 
 // Shared RAM (control input)
+
+#define I2C_CMD_QUIRK       0x02
+
 typedef struct i2c_command {
     // bit[7:0]     status and flags
     // bit[15:8]    write length
@@ -57,6 +60,7 @@ enum {
     I2C_STATE_NXT_QUIRK_WIGGLE,
     I2C_STATE_RX_BYTE,
     I2C_STATE_W_ACK,
+    I2C_STATE_REP_START,
 };
 
 typedef struct i2c_state_struct {
@@ -65,6 +69,7 @@ typedef struct i2c_state_struct {
     uint8_t addr;
     uint8_t wlen;
     uint8_t rlen;
+    uint8_t flags;
 
     uint8_t state;
     uint8_t phase;
@@ -94,8 +99,6 @@ static inline __attribute__((always_inline)) void i2c_hi(uint8_t gpio_bit) {
         :: handle_timeout                               \
     )
 
-uint32_t debug_i;
-
 static void handle_i2c(i2c_state_struct *i2c) {
     uint8_t state = i2c->state;
     uint8_t phase = i2c->phase;
@@ -108,14 +111,15 @@ static void handle_i2c(i2c_state_struct *i2c) {
     switch (state) {
         case I2C_STATE_IDLE: {
             uint32_t flags = SHARED->i2c.flags;
-            if ((flags & 0xff) != 0xaa) {
+            if ((flags & 0x81) != 0x01) {
                 break;
             }
 
             i2c->buffer = SHARED->i2c.buffer;
             i2c->addr = flags >> 24;
             i2c->rlen = flags >> 16;
             i2c->wlen = flags >> 8;
+            i2c->flags = flags;
 
             state = I2C_STATE_START;
             phase = 0;
@@ -216,17 +220,31 @@ static void handle_i2c(i2c_state_struct *i2c) {
 
                 phase = 0;
                 if (i2c->wlen == 0) {
-                    // TODO: Normal repeated start
                     if (state == I2C_STATE_R_ACK_ADDR && i2c->rlen > 0) {
+                        // There is data to be a read, and we just sent the device address.
+                        // We now turn around the bus and get ready for reading.
                         state = I2C_STATE_RX_BYTE;
                         work_bit = 7;
                         work_byte = 0;
                         goto i2c_state_rx;
+                    } else if (i2c->rlen > 0) {
+                        if (i2c->flags & I2C_CMD_QUIRK) {
+                            // The ultrasonic sensor needs a stoP, an extra clock, and then a Start
+                            state = I2C_STATE_STOP;
+                            goto i2c_state_stop;
+                        } else {
+                            state = I2C_STATE_REP_START;
+                            goto i2c_state_rep_start;
+                        }
                     } else {
+                        // Empty ping
                         state = I2C_STATE_STOP;
                         goto i2c_state_stop;
                     }
                 } else {
+                    // There is data to send, either for a "write" type transaction
+                    // or for the initial register number for a "read" type transaction
+                    // before a repeated start (it works the same either way).
                     i2c->wlen--;
                     state = I2C_STATE_TX_BYTE;
                     work_bit = 7;
@@ -252,12 +270,14 @@ static void handle_i2c(i2c_state_struct *i2c) {
                     phase = 0;
                 } else {
                     state = I2C_STATE_IDLE;
-                    SHARED->i2c.flags = 0xaa55;
+                    SHARED->i2c.flags = 0xaa80;
                 }
             }
             break;
 
         case I2C_STATE_NXT_QUIRK_WIGGLE:
+        case I2C_STATE_REP_START:
+i2c_state_rep_start:
             if (phase == 0) {
                 i2c_low(scl_bit);
                 phase = 1;
@@ -333,14 +353,14 @@ static void handle_i2c(i2c_state_struct *i2c) {
 
     if (0) {
 handle_nak:
-        SHARED->i2c.flags = 0x4e55;
+        SHARED->i2c.flags = 0x4e80;
         state = I2C_STATE_IDLE;
     }
 
     if (0) {
 handle_timeout:
         if (--i2c->timeout == 0) {
-            SHARED->i2c.flags = 0x5455;
+            SHARED->i2c.flags = 0x5480;
             state = I2C_STATE_IDLE;
         }
     }