IO/SPI.md

@@ -4,15 +4,33 @@ During SPI interaction we disable interrupts as to reduce the risk of the SD car
 
 ## Commands 
 
-Our implementation realizes a subset of all possible SPI commands, namely the commands required for setting up SPI communication (namely `CMD0`, `CMD1` `CMD8`) and commands needed to read from and write onto an SD card (`CMD17` and `CMD24` respectively). 
-
-| Command | Name |
-| ------ | ------ |
-| CMD0 | GO_IDLE_STATE |
-| CMD1 | SEND_OP_COND |
-| CMD8 | SEND_IF_COND |
-| CMD17 | READ_SINGLE_BLOCK |
-| CMD24 | WRITE_BLOCK |
+Our implementation realizes a subset of all possible SPI commands, namely the commands required for setting up SPI communication (namely `CMD0` and `CMD8`) and commands needed to read from and write onto an SDHC SD card (`CMD17` and `CMD24` respectively). 
+
+| Command | Name | Description |
+| ------ | ------ | ----- |
+| CMD0 | GO_IDLE_STATE | Reset or initialize SD card |
+| CMD8 | SEND_IF_COND | (TODO concise description) |
+| CMD17 | READ_SINGLE_BLOCK | Reads block of 512 bit size. If SDSC card is used, a custom block length can be set by a BLOCK_LEN command. |
+| CMD24 | WRITE_BLOCK | Writes block of 512 bit size. If SDSC card is used, a custom block length can be set by a BLOCK_LEN command. |
+
+## Interaction 
+
+### Initialization: 
+
+Before we can interact with our device we need to run `CMD0` and then `CMD8`. In case of a non-expected response, a step is repeated. 
+
+1. `CMD0` with argument `0x0` and CRC `0x95`. Expected response: `0x01`
+2. `CMD8` with argument `0x000001AA` and CRC `0x87`. Expected response:  `0x01`, and a subsequent echo of the argument. 
+
+TODO: 0x1AA seems to be a common value, others also possible, investigate best practices.
+
+### Reads:
+
+TODO
+
+### Writes: 
+
+TODO
 
 ## Schematics