Simplify the triple buffer implementation

serial_link/protocol/triple_buffered_object.c

@@ -25,28 +25,28 @@ SOFTWARE.
 #include "protocol/triple_buffered_object.h"
 
 #define GET_READ_INDEX() object->state & 3
-#define GET_WRITE1_INDEX() (object->state >> 2) & 3
+#define GET_WRITE_INDEX() (object->state >> 2) & 3
-#define GET_WRITE2_INDEX() (object->state >> 4) & 3
+#define GET_SHARED_INDEX() (object->state >> 4) & 3
-#define GET_FREE_INDEX() (object->state >> 6) & 3
+#define GET_DATA_AVAILABLE() (object->state >> 6) & 1
 
 #define SET_READ_INDEX(i) object->state = ((object->state & ~3) | i)
-#define SET_WRITE1_INDEX(i) object->state = ((object->state & ~(3 << 2)) | (i << 2))
+#define SET_WRITE_INDEX(i) object->state = ((object->state & ~(3 << 2)) | (i << 2))
-#define SET_WRITE2_INDEX(i) object->state = ((object->state & ~(3 << 4)) | (i << 4))
+#define SET_SHARED_INDEX(i) object->state = ((object->state & ~(3 << 4)) | (i << 4))
-#define SET_FREE_INDEX(i) object->state = ((object->state & ~(3 << 6)) | (i << 6))
+#define SET_DATA_AVAILABLE(i) object->state = ((object->state & ~(1 << 6)) | (i << 6))
 
 void triple_buffer_init(triple_buffer_object_t* object) {
     object->state = 0;
-    SET_WRITE1_INDEX(0);
+    SET_WRITE_INDEX(0);
-    SET_WRITE2_INDEX(0);
     SET_READ_INDEX(1);
-    SET_FREE_INDEX(2);
+    SET_SHARED_INDEX(2);
+    SET_DATA_AVAILABLE(0);
 }
 
 static void triple_buffer_begin_read(uint16_t object_size, triple_buffer_object_t* object) {
-    uint8_t newest = GET_WRITE2_INDEX();
+    uint8_t shared_index = GET_SHARED_INDEX();
-    uint8_t free_index = GET_READ_INDEX();
+    uint8_t read_index = GET_READ_INDEX();
-    SET_READ_INDEX(newest);
+    SET_READ_INDEX(shared_index);
-    SET_FREE_INDEX(free_index);
+    SET_SHARED_INDEX(read_index);
 }
 
 static void triple_buffer_actual_read(uint16_t object_size, triple_buffer_object_t* object, void* dst) {
@@ -58,22 +58,12 @@ static void triple_buffer_end_read(uint16_t object_size, triple_buffer_object_t*
 }
 
 void triple_buffer_write(uint16_t object_size, triple_buffer_object_t* object, void* src) {
-    uint8_t write1_index = GET_WRITE1_INDEX();
-    uint8_t write2_index = GET_WRITE2_INDEX();
-    uint8_t read_index = GET_READ_INDEX();
-    uint8_t free_index = GET_FREE_INDEX();
 
-    if (write2_index == read_index) {
+    uint8_t write_index = GET_WRITE_INDEX();
-        // We are reading from the other write index
+    memcpy(object->buffer + object_size * write_index, src, object_size);
-        SET_WRITE1_INDEX(free_index);
+    uint8_t shared_index = GET_SHARED_INDEX();
-        memcpy(object->buffer + object_size * free_index, src, object_size);
+    SET_SHARED_INDEX(write_index);
-        SET_WRITE2_INDEX(free_index);
+    SET_WRITE_INDEX(shared_index);
-    }
-    else {
-        SET_WRITE1_INDEX(write2_index);
-        memcpy(object->buffer + object_size * write2_index, src, object_size);
-        SET_WRITE2_INDEX(write2_index);
-    }
 }
 
 void triple_buffer_read(uint16_t object_size, triple_buffer_object_t* object, void* dst) {

serial_link/tests/triple_buffered_object_tests.c

@@ -77,4 +77,22 @@ Ensure(TripleBufferedObject, performs_another_write_in_the_middle_of_read) {
     triple_buffer_actual_read(4, (triple_buffer_object_t*)&test_object, &dst);
     triple_buffer_end_read(4, (triple_buffer_object_t*)&test_object);
     assert_that(dst, is_equal_to(1));
+    triple_buffer_read(4, (triple_buffer_object_t*)&test_object, &dst);
+    assert_that(dst, is_equal_to(2));
+}
+
+Ensure(TripleBufferedObject, performs_two_writes_in_the_middle_of_read) {
+    uint32_t src = 1;
+    uint32_t dst;
+    triple_buffer_write(4, (triple_buffer_object_t*)&test_object, &src);
+    triple_buffer_begin_read(4, (triple_buffer_object_t*)&test_object);
+    src = 2;
+    triple_buffer_write(4, (triple_buffer_object_t*)&test_object, &src);
+    src = 3;
+    triple_buffer_write(4, (triple_buffer_object_t*)&test_object, &src);
+    triple_buffer_actual_read(4, (triple_buffer_object_t*)&test_object, &dst);
+    triple_buffer_end_read(4, (triple_buffer_object_t*)&test_object);
+    assert_that(dst, is_equal_to(1));
+    triple_buffer_read(4, (triple_buffer_object_t*)&test_object, &dst);
+    assert_that(dst, is_equal_to(3));
 }