[SC64][DOCS] USB command arguments description (time and CIC params) (#35)

Work in progress, criticism/corrections welcome.

---------

Co-authored-by: Mateusz Faderewski <sc@mateuszfaderewski.pl>

docs/02_usb_commands.md

@@ -1,4 +1,8 @@
 - [USB commands](#usb-commands)
+- [USB command arguments](#usb-command-arguments)
+  - [**TIME_GET**](#t-time_get)
+  - [**TIME_SET**](#t-time_set)
+  - [**CIC_PARAMS_SET**](#b-cic_params_set)
 
 ---
 
@@ -9,13 +13,13 @@
 | `v` | **IDENTIFIER_GET**     | ---          | ---          | ---  | identifier       | Get flashcart identifier `SCv2`                               |
 | `V` | **VERSION_GET**        | ---          | ---          | ---  | version          | Get flashcart firmware version                                |
 | `R` | **STATE_RESET**        | ---          | ---          | ---  | ---              | Reset flashcart state (CIC params and config options)         |
-| `B` | **CIC_PARAMS_SET**     | cic_params_0 | cic_params_1 | ---  | ---              | Set CIC emulation parameters (disable/seed/checksum)          |
+| `B` | [**CIC_PARAMS_SET**](#b-cic_params_set) | cic_params_0 | cic_params_1 | ---  | ---              | Set CIC emulation parameters (disable/seed/checksum)          |
 | `c` | **CONFIG_GET**         | config_id    | ---          | ---  | current_value    | Get config option                                             |
 | `C` | **CONFIG_SET**         | config_id    | new_value    | ---  | ---              | Set config option                                             |
 | `a` | **SETTING_GET**        | setting_id   | ---          | ---  | current_value    | Get persistent setting option                                 |
 | `A` | **SETTING_SET**        | setting_id   | new_value    | ---  | ---              | Set persistent setting option                                 |
-| `t` | **TIME_GET**           | ---          | ---          | ---  | time             | Get current RTC value                                         |
+| `t` | [**TIME_GET**](#t-time_get) | ---          | ---          | ---  | time             | Get current RTC value                                         |
-| `T` | **TIME_SET**           | time_0       | time_1       | ---  | ---              | Set new RTC value                                             |
+| `T` | [**TIME_SET**](#t-time_set) | time_0       | time_1       | ---  | ---              | Set new RTC value                                             |
 | `m` | **MEMORY_READ**        | address      | length       | ---  | data             | Read data from specified memory address                       |
 | `M` | **MEMORY_WRITE**       | address      | length       | data | ---              | Write data to specified memory address                        |
 | `U` | **USB_WRITE**          | type         | length       | data | N/A              | Send data to be received by app running on N64 (no response!) |
@@ -27,3 +31,49 @@
 | `F` | **FIRMWARE_UPDATE**    | address      | length       | ---  | status           | Update firmware from specified memory address                 |
 | `?` | **DEBUG_GET**          | ---          | ---          | ---  | debug_data       | Get internal FPGA debug info                                  |
 | `%` | **STACK_USAGE_GET**    | ---          | ---          | ---  | stack_usage      | Get per task stack usage                                      |
+
+---
+
+## USB command arguments
+
+What follows is the description of the command arguments' bit fields.
+
+These arguments are encoded in big-endian, and are laid out as such:
+
+| | arg0 | arg1 |
+| --- | --- | --- |
+| bits | `[63:32]` | `[31:0]` |
+
+---
+
+### `B`: [**CIC_PARAMS_SET**](https://github.com/Polprzewodnikowy/SummerCart64/blob/v2.12.1/sw/controller/src/cic.c#L337)
+
+| bits | description |
+| ---  | --- |
+| `[56]` | Disable CIC |
+| `[55:48]` | CIC seed (IPL2 and IPL3 stages) |
+| `[47:0]` | Checksum |
+
+---
+
+### `t`: [**TIME_GET**](https://github.com/Polprzewodnikowy/SummerCart64/blob/v2.12.1/sw/controller/src/cfg.c#L410)
+
+Same as [**TIME_SET**](#t-time_set).
+
+---
+
+### `T`: [**TIME_SET**](https://github.com/Polprzewodnikowy/SummerCart64/blob/v2.12.1/sw/pc/sc64.py#L795)
+
+Date values use the [BCD](https://en.wikipedia.org/wiki/Binary-coded_decimal) format.
+
+([RTC chip specifications](https://ww1.microchip.com/downloads/aemDocuments/documents/MPD/ProductDocuments/DataSheets/MCP7940N-Battery-Backed-I2C-RTCC-with-SRAM-20005010J.pdf))
+
+| bits | description |
+| ---  | --- |
+| `[63:56]` | Week day, starting at 1 (user-defined representation) |
+| `[55:48]` | Hours |
+| `[47:40]` | Minutes |
+| `[39:32]` | Seconds |
+| `[23:16]` | Year (from 0 to 99) |
+| `[15:8]` | Month |
+| `[7:0]` | Day |