gudt/docs/flags.md

Node Flags

When a node's type isn't zero, then it is a resource node with a flags field. This flags field has two values:

• bit 0..3: lower tetrad GUDT_F_UNIT, encodes unit size in shift bits: 0 = 8 bit, 1 = 16 bit, 2 = 32 bit, 3 = 64 bit, etc.
• bit 4..7: upper tetrad GUDT_F_DATA, if 0 then unit is alignment, otherwise this is the number of unit sized items inlined.

Resource Descriptor

Most common case, upper tetrad is zero and lower tetrad is not 0x0f and encodes alignment. What address space is used for the base address depends on type: MMIO, IO port, IRQ, NVRAM/CMOS, etc.

Offset	Size	Description
0	1	type != 0 resource node
1	1	flags (bit 0..3: alignment, bit 4..7: 0)
2	2	parent node
4	4	size field
8	8	address field

{
    "unit": "byte" / "word" / "dword" / "qword" / "m128" / "m256" / "m512" / "m1024",
    "size": (number) size,
    "base": (number) address
}

Indirect Reference

When the flags field is 0x0f GUDT_F_INDIRECT. Here the size field points to another resource node.

Offset	Size	Description
0	1	type != 0 resource node
1	1	flags = 0x0f
2	2	parent node
4	4	another resource node id
8	8	bitmask if not 0

{
    "unit": "indirect",
    "node": (number) pointed node
}

or

{
    "unit": "indirect",
    "node": (number) pointed node,
    "mask": (number) bitmask
}

Inlined Data

When the upper tetrad isn't zero then it is the number of inlined items and then lower tetrad encodes item size.

Offset	Size	Description
0	1	type != 0 resource node
1	1	flags (bit 0..3: item size, bit 4..7: number of items)
2	2	parent node
4	12	inlined data array

{
    "unit": "byte" / "word" / "dword" / "qword",
    "data": [ (number) list of values ]
}

If a resource needs more than 12 inlined bytes or 6 words, 3 dwords or 1 qword, then simply more nodes are added to the list. With qword items, size is always zero and a single qword data item is stored in the base field.