Update 'USB protocol'

USB-protocol.md

@@ -69,10 +69,79 @@ Note: the serial number matches the one on the sticker on the bottom of the plas
 
 ### Protocol
 
-The device operates in two (or three, depending on how you count) operting modes: bootloader mode (and authenticated bootloader mode), and application mode.
+The device operates in two (or three, depending on how you count) operting modes: bootloader mode (and authenticated bootloader mode), and application mode. By default, the device starts in 'unauthenticated' bootloader mode.
 
 In bootloader mode, you first have to send a magic number for the device (stored in the FT240X' EEPROM) to enable some functionality: when authenticated, in bootloader mode, you can access the Spartan-3AN's internal SPI flash, as well as maybe a few extra bits.
 
 You can switch to application mode (and back to bootloader mode) at any time, however, allegedly (this is the behavior of the [ScanaPLUS](https://sigrok.org/wiki/IKALOGIC_ScanaPLUS) device, which has a similar setup) capturing samples (in application mode) will not work when not authenticated in bootloader mode. (TODO: does switching to bootloader mode from application mode bring you into authenticated mode when already authenticated before switching to application mode?)
 
-TODO: document the commands of every mode
+A log of libftd2xx function calls from ScanaStudio, in various scenarios, is available [here](https://cloud.lain.faith/s/RpcBp89MA2LDqqY).
+
+Commands are typically a one-byte command ID, followed by a variable amount of data bytes.
+
+#### Mode-independent
+
+* **`0xfd`: Get status/mode**
+  * Arguments: *fixed* `0x00 0x01 0x02 0xfe`
+  * Response:
+    * Unauthenticated bootloader mode: `0x09 0x09 0x09 0x09`
+    * Authenticated bootloader mode: `0x01 0x01 0x01 0x01`
+    * Application mode: `0x22 0x22 0x22 0x22`
+* **`0x93`: Reset to application mode**
+  * No arguments
+  * No response
+* **`0x94`: Reset to bootloader mode**
+  * No arguments
+  * No response
+
+#### Bootloader mode
+
+* **`0xf1`: Send unlock/authentication code**
+  * Arguments: 3 bytes from [FT240X EEPROM](FT240X-EEPROM) word locations `0x12:0x13`, followed by a *fixed* 23 zero bytes
+  * No response
+* **`0x90`: Spartan-3AN internal SPI flash chip select**
+  * Arguments: *fixed* `0x00`
+  * No response
+* **`0x91`: Spartan-3AN internal SPI flash chip deselect**
+  * Arguments: *fixed* `0x00`
+  * No response
+* **`0x92`: Spartan-3AN internal SPI flash chip data transfer**
+  * Arguments: single byte to send (`0xff` for SPI read operations)
+  * Response: single byte result of the SPI operation (garbage if the byte transferred was meant as a write)
+  * Yes, SPI transfers are done byte-by-byte this way. For details on how to communicate with the Spartan-3AN internal flash, see [Xilinx docs (UG333)](https://www.xilinx.com/support/documentation/user_guides/ug333.pdf). See the "Example transfers" section below.
+
+#### Application mode
+
+TODO lol
+
+#### Example transfers
+
+##### Spartan-3AN internal SPI flash read ID and status
+
+```
+Flash ID:
+  Send 0x90,0x00, no read data
+  Send 0x92,0x9f, read 1 byte and discard it
+  Send 0x92,0xff, read 1 data byte
+  Send 0x92,0xff, read 1 data byte
+  Send 0x91,0x00, no read data
+Status:
+  Send 0x90,0x00, no read data
+  Send 0x92,0xd7, read 1 byte and discard it
+  Send 0x92,0xff, read 1 data byte
+  Send 0x91,0x00, no read data
+```
+
+##### Spartan-3AN internal SPI flash dump
+
+```
+Send 0x90,0x00, no read data
+Send 0x92,0x0b, read 1 byte and discard it
+Send 0x92,0x00, read 1 byte and discard it
+Send 0x92,0x00, read 1 byte and discard it
+Send 0x92,0x00, read 1 byte and discard it
+Send 0x92,0xff, read 1 byte and discard it
+Repeat 135168 times:
+  Send 0x92,0xff, read 1 data byte
+Send 0x91,0x00, no read data
+```