Further cleanup

datagram.md

@@ -3,23 +3,26 @@
 Unlike the remote api with its many functions, this has only two, send and receive a message.
 You must write a custom program running on the AMMDK k66f to make any practical use of this functionality.
 
-[`test/blip-test.cpp`] is an example of a program that uses this API.
+[`test/blip-test.cpp`](test/blip-test.cpp) is an example of a program that uses this API.
 It requires `heartrateLED.elf` from the `amm-tiny` repo to be on the k66f.
 
 ## Functions
 
-`send_message(uint8_t *buf, size_t len)` sends the data in `buf`. `len` contains the length of the buffer. Returns:
+#### `send_message(uint8_t *buf, size_t len)`
+`send_message` sends the data in `buf`. `len` contains the length of the buffer. `send_message` returns:
 
 * 0 if message was sent successfully
 * -1 if `len` > `SPI_MSG_PAYLOAD_LEN`
 * -2 if no space available to send message
 
+#### `spi_callback`
 The `spi_callback` variable is a callback for received messages.
 
     extern void (*spi_callback)(struct spi_packet*);
 
 This function receives the protocol information as well as payload, which is in field `msg` of the argument.
 `msg` is declared `uint8_t msg[SPI_MSG_PAYLOAD_LEN];`.
-If you do not need to receive messages, it can be `NULL` but it must be present.
+If you do not need to receive messages, `spi_callback` may be `NULL` but it must be present.
 
-`void datagram_task(void)` should be called as a thread, e.g. `std::thread thread(datagram_task);`, and must be running before `send_message` is called.
+#### `void datagram_task(void)`
+This task should be called as a thread, e.g. `std::thread thread(datagram_task);`, and must be running before `send_message` is called.