HIPC

IPC Command Structure

This is an array of u32's.

Word	Bits	Description
0	15-0	IPC version? Always 4.
0	19-16	Number of buf X descriptors (each: 2 words).
0	23-20	Number of buf A descriptors (each: 3 words).
0	27-24	Number of buf B descriptors (each: 3 words).
0	31-28	Number of type W desciptors (each: 3 words), never observed.
1	9-0	Size of data portion in u32's.
1	13-10	If set to 2, enable buf C descriptor.
1	31	Enable handle descriptor.
...		Handle descriptor, if enabled.
...		Buf X descriptors, each one 2 words.
...		Buf A descriptors, each one 3 words.
...		Buf B descriptors, each one 3 words.
...		Type W descriptors, each one 3 words.
...		Padding
...		Raw data
...		Buf C descriptors, each one 2 words.

Handle descriptor

There can only be one of this descriptor type. It is enabled by bit31 of the second word.

Word	Bits	Description
0	0	Send current PID.
0	4-1	Number of handles.
0	8-5	Number of B-words for this special descriptor.
...		Handles
...		B-words, purpose unknown.

Buffer descriptor A/B

This packing is so unnecessarily complex.

Word	Bits	Description
0		Lower 32-bits of size.
1		Lower 32-bits of address.
2	1-0	Always set to 1 or 3. R/RW.
2	4-2	Bit 38-36 of address.
2	27-24	Bit 35-32 of size.
2	31-28	Bit 35-32 of address.

Buffer descriptor C

Word	Bits	Description
0		Lower 32-bits of address.
1	15-0	Rest of address.
1	31-16	Size

Buffer descriptor X

This one is packed even worse than A, they inserted the bit38-36 of the address on top of the counter field.

Word	Bits	Description
0	5-0	Bits 5-0 of counter.
0	8-6	Bit 38-36 of address.
0	11-9	Bits 11-9 of counter.
0	15-12	Bit 35-32 of address.
0	31-16	Size
1		Lower 32-bits of address.

Raw data portion

This is an array of u64's. It's always aligned to 16 so sometimes there is padding words before it.

Word	Description	...	Two words are reserved here to receive PID if enabled.
0	Magic ("SFCI" for requests, "SFCO" for responses)
1	Cmd id
...	Non-marshalled data is placed here

Official marshalling code

The official marshalling function takes an array of (buf_ptr, size) pairs and a type-field for each such pair.

Bitmask 0x10 seems to indicate null-terminated strings, but that flag is ignored by the marshalling code.

Type Mask	Description
4 + 1	Creates an A descriptor
4 + 2	Creates a B descriptor
8 + 1	Creates an X descriptor
8 + 2	Creates a C descriptor
0x20 + 1	Creates both an A and X descriptor