IPC

The IPC commands are written to the Thread Local Storage, at offset 0x80. Every IPC command sent to services starts with a u32 header code, and parameters, if any, are written after this header. If the kernel was able to dispatch the request, the server reply will be written to TLS+0x80. Often the first word of the response data is the error code (or 0 if success).

The command header is a 32-bit integer that can be decompossed in the following parts:

Bits	Description
0-5	Number of translate parameters (=y)
6-11	Number of normal parameters (=x)
12-15	Unused
16-31	Command ID

The entire command has the following structure:

Word	Size	Description
0	1	Header code
1	x	Normal parameters
x	y	Translate parameters

Translate parameters are modified/translated transparently by the kernel. They are used to transfer handles/buffers between the different processes.

The type of parameter is described by the bits 1-3 in the translation descriptor. Parameter types accepted for sending by the kernel are: 0, 1, 2, 5, 6, 7. Type 0 is used to send handles across processes:

if desc & 0x30 == 0x20:
  write process id to value
else:
  translate handle
  if desc & 0x30 == 0x10:
    close handle for caller

For replies, only 0, 1, 5, 6, 7 are allowed. In other words any type 2 fields must be zeroed before calling svcReplyAndReceive on the server-side. For replies type 0, 1, 2 are ignored. Types 5, 6, 7 do something with the mem pointer upon reply. The type 0 descriptor can be used to ignore parameters. The number of parameters covered by a type-0 descriptor is (desc >> 26) + 1.

Type	Usual form	Description
0	0x00000000 <handle>	The corresponding value is a KHandle, that should be closed in calling process. Or zero otherwise.
0	0x00000010 <handle>	The corresponding value is a KHandle, that will be duplicated. Or zero otherwise.
0	0x00000020 <placeholder>	Let kernel set value to calling process ProcessID.
1	0x00000002 | (size<<14) | (static_buffer_id<<10) <ptr>	The corresponding value contains a ptr to a buffer of said size, that should be copied to an already set-up buffer in destination process at Thread Local Storage offset 0x180 + static_buffer_id*8. The static_buffer_id is only 4 bits, making it possible for at most up to 16 buffers in total per thread.
2	0x00000004 | (size<<4)	This is used for PXI commands input/output buffers. The address written to the destination cmd-buf is a phys-addr for a table located in the BASE memregion. This table contains the phys-addrs for the actual data, the array entries have the following format: {u32 *datachunk_physaddr, u32 datachunk_bytesize}.
3	0x00000006	Does nothing?
4	0x00000008	This command will cause a kernelpanic.
5	0x0000000A | (size<<4) <ptr>	The corresponding value contains a ptr to a buffer of said size. It is mapped R- in the destination process??
6	0x0000000C | (size<<4) <ptr>	The corresponding value contains a ptr to a buffer of said size. It is mapped -W in the destination process??
7	0x0000000E | (size<<4) <ptr>	The corresponding value contains a ptr to a buffer of said size. It is mapped RW in the destination process??

Buffers from commands 5,6,7 will get mapped at virtual address 0x04000000+ in destination process.