One symbol in USB-sysmodule is: "vtable for nn::usb::detail::UsbComplexTegra21x".

usb:ds

Used for Switch<>PC USB comms, aka Switch-as-device. This service is used during factory setup by manu.

This service session is used as an IPC domain by manu. All of these {get-session} commands also return an output u8 and the u32 <domainID>, for using those sessions as domains.

Cmd	Name	Notes
0	#BindDevice
1	#BindClientProcess
2	#GetDsInterface
3	#GetStateChangeEvent
4	#GetState
5	#SetVidPidBcd

Initialization done by manu:

Initial service init:
- Get service/etc.
- Uses #BindDevice.
- Uses #BindClientProcess.
- Uses #GetStateChangeEvent.
- Uses #SetVidPidBcd.
Interface init:
- Uses #GetDsInterface, then uses commands from that with the rest of the following.
- Uses #GetSetupEvent.
- Uses #GetCtrlInCompletionEvent.
- Uses #GetCtrlOutCompletionEvent.
Initializes two endpoints via using #GetDsEndpoint twice.

Configuration

The following is the default USB config strings, while the usbds service isn't being used. All of the below configuration will reset to the defaults when all usbds-related sessions are closed. These can be set with #SetVidPidBcd. The default string for Product is loaded from settings config. The default is referred to by usb-sysmodule as "Dummy".

 Product: Nintendo Switch
 Manufacturer: Nintendo
 SerialNumber: SerialNumber

The following is the default lsusb -v {...} output when the usbds service wasn't used.

The endpoints are configured using #GetDsEndpoint, the total number of endpoints is the number of open #IDsEndpoint sessions. bInterfaceNumber is {0-based index for the enabled #IDsInterface session.} Some of the interface fields are configured using #GetDsInterface.

Additional descriptors for use with interfaces/endpoints can't be configured with usbds, even though the former is used for the default HID interface. This seems to be the main(?) restriction with using usbds for Switch-as-arbitrary-devices. The device class fields can't be configured, interface class fields are set instead.

 Bus 003 Device 006: ID 057e:2000 Nintendo Co., Ltd 
 Couldn't open device, some information will be missing
 Device Descriptor:
   bLength                18
   bDescriptorType         1
   bcdUSB               2.00
   bDeviceClass            0 (Defined at Interface level)
   bDeviceSubClass         0 
   bDeviceProtocol         0 
   bMaxPacketSize0        64
   idVendor           0x057e Nintendo Co., Ltd
   idProduct          0x2000 
   bcdDevice            1.00
   iManufacturer           1 
   iProduct                2 
   iSerial                 3 
   bNumConfigurations      1
   Configuration Descriptor:
     bLength                 9
     bDescriptorType         2
     wTotalLength           34
     bNumInterfaces          1
     bConfigurationValue     1
     iConfiguration          0 
     bmAttributes         0xc0
       Self Powered
     MaxPower              {...}
     Interface Descriptor:
       bLength                 9
       bDescriptorType         4
       bInterfaceNumber        0
       bAlternateSetting       0
       bNumEndpoints           1
       bInterfaceClass         3 Human Interface Device
       bInterfaceSubClass      0 No Subclass
       bInterfaceProtocol      0 None
       iInterface              0 
         HID Device Descriptor:
           bLength                 9
           bDescriptorType        33
           bcdHID               2.00
           bCountryCode            0 Not supported
           bNumDescriptors         1
           bDescriptorType        34 Report
           wDescriptorLength      26
          Report Descriptors: 
            ** UNAVAILABLE **
       Endpoint Descriptor:
         bLength                 7
         bDescriptorType         5
         bEndpointAddress     0x81  EP 1 IN
         bmAttributes            3
           Transfer Type            Interrupt
           Synch Type               None
           Usage Type               Data
         wMaxPacketSize     0x0001  1x 1 bytes
         bInterval              16

BindDevice

Takes an u32 (complexId). Manu sends 0x02.

Binding more than once with the current session is not allowed. Once this command is used, the USB device will not be listed with lsusb until #EnableInterface is used.

Returns a not-found error when complexId isn't 0x02, for values 0x0-0x4 (while in handheld-mode at least).

BindClientProcess

Takes 1 copy-handle for the current process (0xFFFF8001).

GetDsInterface

Takes 2 type-5 buffers and returns an #IDsInterface. Manu sends a 0x09-byte command (e.g.: 0x09, 0x04, 0x04, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0x00) in the first buffer and a string ("usb") in the second buffer.

When the strlen output for the second buffer is >=0x40, size 0x40 is used instead for copying the string. This is the interface name, it's not sent over USB.

Returns an error when #BindDevice wasn't used.

Up to 4 interfaces can be used+enabled.

Structure of the first buffer(this is the same as libusb__interface__descriptor):

Offset	Size	Description
0x0	0x1	bLength. Must match 0x9.
0x1	0x1	bDescriptorType. Must match 0x4.
0x2	0x1	bInterfaceNumber. When 0x4, the bInterfaceNumber is automatically allocated(error will be thrown if no space). Otherwise, it's used directly and must be <=3.
0x3	0x1	bAlternateSetting. Must match 0x0.
0x4	0x1	bNumEndpoints. Ignored.
0x5	0x1	bInterfaceClass
0x6	0x1	bInterfaceSubClass
0x7	0x1	bInterfaceProtocol
0x8	0x1	iInterface. Ignored.

Only the first 0x9-bytes are used.

GetStateChangeEvent

Returns an event handle for when the state returned by #GetState changes. Signalled when Switch<->host USB comms change between started/stopped. USB cable connected/disconnected while at least 1 interface was enabled, or interface enabled/disabled while the USB cable was connected which then caused USB-comms state to change.

GetState

No input. Returns an output u32. Returns an error when #BindDevice wasn't used.

Returns the current state. Values:

0: Initial state.
6: Device init starting.
3: {Initialization}, previous state is 6.
4: {Initialization}, previous state is 3.
5: Initialization done, data-transfer is now available.

SetVidPidBcd

Takes a type-5 buffer with 0x66 bytes of USB descriptor data (see manu).

Offset	Size	Description
0x0	0x2	VID (idVendor)
0x2	0x2	PID (idProduct)
0x4	0x2	bcdDevice
0x6	0x20	Manufacturer
0x26	0x20	Product
0x46	0x20	SerialNumber

The last 3 blocks are ASCII strings. The data following each string is all-zero, for padding to size 0x20.

IDsInterface

Cmd	Name	Notes
0	#GetDsEndpoint
1	#GetSetupEvent
2		Takes a type-0x6 output buffer, no other output. Memcpys data to outbuf with outsize, uses size 0x8 if outsize is too large.
3	#EnableInterface
4	#DisableInterface
5	#CtrlInPostBufferAsync
6	#CtrlOutPostBufferAsync
7	#GetCtrlInCompletionEvent
8	#GetCtrlInReportData
9	#GetCtrlOutCompletionEvent
10	#GetCtrlOutReportData
11	#StallCtrl

Commands cmd2, #CtrlInPostBufferAsync, #CtrlOutPostBufferAsync, and #StallCtrl, will throw an error if the interface is not enabled. #GetDsEndpoint will throw an error if the interface is enabled.

GetDsEndpoint

Takes a type-5 buffer and returns an #IDsEndpoint. Manu uses this twice for getting two endpoint sessions, with the following 0x7-byte buffer data:

First endpoint: 0x07, 0x05, 0x80, 0x02, 0x00, 0x02, 0x00
- bLength=0x7
- bDescriptorType=LIBUSB_DT_ENDPOINT
- bEndpointAddress=LIBUSB_ENDPOINT_IN
- bmAttributes=LIBUSB_TRANSFER_TYPE_BULK
- wMaxPacketSize=0x200
- bInterval=0
Second endpoint: Same as above except byte2 is 0x00(bEndpointAddress=LIBUSB_ENDPOINT_OUT).

Each field is an u8, except for offset 0x4-0x5 which is an u16.

This structure matches libusb_endpoint_descriptor, with audio-only-devices fields bRefresh and bSynchAddress removed.

The buffer size must be >=0x7. Only the first 0x7-bytes from the buffer are used.

Byte0(bLength) must match 0x7.
Byte1(bDescriptorType) must match 0x5.
Byte2(bEndpointAddress) is only compared with 0x80 to determine whether to use an input or output endpoint, the actual endpoint-number is allocated automatically by checking state. Hence, all input endpoints must use bEndpointAddress==0x80. Up to endpoint-number 0xF can be allocated for each endpoint-direction, for a total of 16 endpoints including control, and 15 for non-control endpoints(#IDsEndpoint sessions for each direction). This matches the Tegra maximum.

From the Tegra datasheet: "The maximum packet size supported on any endpoint is 1024 bytes in high-speed mode, for both device and host modes."

GetSetupEvent

Returns an event handle. Unknown what triggers signalling, not signalled during interface-enable / device<>host USB-comms init.

EnableInterface

Takes no arguments. Enables the current interface.

Only one interface can be enabled at a time per bInterfaceNumber. When bInterfaceNumber is auto-allocate(0x4) for #GetDsEndpoint this isn't an issue since the final bInterfaceNumber will be unique.

Once enabled, the device/interface can then actually be used over USB.

DisableInterface

Takes no arguments. Disables the current interface.

CtrlInPostBufferAsync

Same as #PostBufferAsync(with same input/output), except this uses control input endpoint 0x80.

CtrlOutPostBufferAsync

Same as #PostBufferAsync(with same input/output), except this uses control output endpoint 0x00.

GetCtrlInCompletionEvent

Returns an event handle for polling the completion of input control commands. Same as #GetCompletionEvent, except this uses control input endpoint 0x80.

GetCtrlInReportData

Same as #GetReportData(with same input/output), except this uses control input endpoint 0x80.

GetCtrlOutCompletionEvent

Returns an event handle for polling the completion of output control commands. Same as #GetCompletionEvent, except this uses control output endpoint 0x00.

GetCtrlOutReportData

Same as #GetReportData(with same input/output), except this uses control output endpoint 0x00.

StallCtrl

No input/output.

Calls a function with both control endpoints(0x80 and 0x00) with the same function. From strings: "m_pProtocol->Stall(0x80)" "m_pProtocol->Stall(0x00)".

IDsEndpoint

Cmd	Name	Notes
0	#PostBufferAsync
1		No input/output.
2	#GetCompletionEvent
3	#GetReportData
4	#Stall
5		Takes an input u8, no output.

PostBufferAsync

Takes an u32 (size) and an u64 (buffer). Returns an output u32 (urbId). The output urbId can then be used while parsing the output of #GetReportData, after waiting for the CompletionEvent to be signalled.

The buffer address must be 0x1000-byte aligned. The input size doesn't matter.

Used for data-transfer with input/output endpoints.

The user-process must flush dcache for the buffer before using this command.

When sending data where size is larger than wMaxPacketSize, it will automatically send multiple USB packets where last packet size = {remaining size}. Every {wMaxPacketSize}-bytes is a different packet.

For receiving data, if size is less than {actual received USB packet size} the rest of the packet will be discarded. Later PostBufferAsync cmd(s) will only return data from new packets, not the remainder of the earlier packet(s).

GetCompletionEvent

No input. Returns an output event handle for polling the completion of #PostBufferAsync, even when it finished via #Stall.

GetReportData

No input. Returns 0x84 bytes of report data from the endpoint. Seems to be eventually loaded from state, since this doesn't trigger any USB bus activity. All-zero before PostBufferAsync was used at least once.

Offset	Size	Description
0x0	0x10*0x8(0x80)	0x8 entries 0x10-bytes each for each report.
0x80	0x4	u32 report count

Entry data:

Offset	Size	Description
0x0	0x4	u32 id (urbId from post-buffer commands)
0x4	0x4	u32 requestedSize
0x8	0x4	u32 transferredSize
0xC	0x4	u32 urb status, converted to error-codes. 0x3 = success, 0x4 = 0x828c, 0x5 = 0x748c. All other values are invalid.

Stall