Hardware/Latte IPC

Latte IPC
Latte Registers
Access
Espresso	Partial
Starbuck	Full
Registers
Base	0x0d800000, 0x0d800400
Length	0x10, 0x30
Access size	32 bits
Byte order	Big Endian
IRQs
Espresso	9, 10, 11
Latte	30, 31

The Latte's IPC engine is generally used as a signalling system for communications between the PPC and ARM. The hardware consists of two general-purpose registers, and two flag pairs. Each side can set either of two flags, and the other side can read them or clear them and configure them to generate a Latte interrupt. The hardware is symmetric.

Operation

Conceptually, the IPC system can be seen as four bit flags which may be set or cleared: X1, X2, Y1, and Y2. These same four flags are visible in both control registers in different places. X1 and X2 can be read/set/cleared by the Espresso, but can only be read/cleared by the Starbuck. The Starbuck can configure individually whether X1 or X2 generate an interrupt (#31). The opposite is true for Y1 and Y2: they can be read/set/cleared by the Starbuck, but only read/cleared by the Espresso. The Espresso can configure whether these generate an interrupt (#30).

Note that, since the interrupts can actually route to either or both the Starbuck and Espresso, and since the Starbuck can also access the Espresso's registers, there are ways of abusing these flags for odd purposes.

Register LT_IPC_ARMCTRL can only be accessed by the Starbuck. The other three registers can be accessed by both CPUs.

Register List

The Latte IPC engine has two different register blocks: a global ARM block mapped at the same address as on the Wii, and a new SMP block for each PPC core to use. Each core's region of the SMP block has registers equivalent to the global ARM block.

Global ARM block

Global ARM block
Address	Bits	Name	Description
0x0d800000	32	LT_IPC_PPCMSG	Espresso data register
0x0d800004	32	LT_IPC_PPCCTRL	Espresso flags and control
0x0d800008	32	LT_IPC_ARMMSG	Starbuck data register
0x0d80000c	32	LT_IPC_ARMCTRL	Starbuck flags and control

SMP block

SMP block - PPC core 0
Address	Bits	Name	Description
0x0d800400	32	LT_IPC_PPC0_PPCMSG	Espresso data register for PPC core 0
0x0d800404	32	LT_IPC_PPC0_PPCCTRL	Espresso flags and control for PPC core 0
0x0d800408	32	LT_IPC_PPC0_ARMMSG	Starbuck data register for PPC core 0
0x0d80040c	32	LT_IPC_PPC0_ARMCTRL	Starbuck flags and control for PPC core 0

SMP block - PPC core 1
Address	Bits	Name	Description
0x0d800410	32	LT_IPC_PPC1_PPCMSG	Espresso data register for PPC core 1
0x0d800414	32	LT_IPC_PPC1_PPCCTRL	Espresso flags and control for PPC core 1
0x0d800418	32	LT_IPC_PPC1_ARMMSG	Starbuck data register for PPC core 1
0x0d80041c	32	LT_IPC_PPC1_ARMCTRL	Starbuck flags and control for PPC core 1

SMP block - PPC core 2
Address	Bits	Name	Description
0x0d800420	32	LT_IPC_PPC2_PPCMSG	Espresso data register for PPC core 2
0x0d800424	32	LT_IPC_PPC2_PPCCTRL	Espresso flags and control for PPC core 2
0x0d800428	32	LT_IPC_PPC2_ARMMSG	Starbuck data register for PPC core 2
0x0d80042c	32	LT_IPC_PPC2_ARMCTRL	Starbuck flags and control for PPC core 2

Register Details

LT_IPC_PPCMSG (0x0d800000)
	310
Access	R/W

This is a general purpose 32-bit register that can be freely read/written by both CPUs. It is usually set by the Espresso and read by the Starbuck, though this is not a requirement. In IOSU, this register contains a pointer to a 0x48-byte structure in memory.

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LT_IPC_PPCCTRL (0x0d800004)
	31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16
Access	U
Field
	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Access	U										R/W	R/W	R/W	R/Z	R/Z	R/W
Field											IY2	IY1	X2	Y1	Y2	X1

Field	Description
X1	Read/write flag X1
Y2	Read flag Y2. To clear the flag, write 1 to this bit.
Y1	Read flag Y1. To clear the flag, write 1 to this bit.
X2	Read/write flag X2
IY1	If set, flag Y1 generates Latte interrupt #30
IY2	If set, flag Y2 generates Latte interrupt #30

This register exposes the Espresso side of the IPC control. Flags X1 and X2 may be freely set/cleared. Flags Y1 and Y2 can be read and cleared (by writing one), and can optionally generate IRQ #30.

IOS usage

Field	Description
X1	Execute command: a new pointer is available in LT_IPC_PPCCTRL
Y2	Command acknowledge
Y1	Command executed and reply available in LT_IPC_ARMMSG
X2	Relaunch

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LT_IPC_ARMMSG (0x0d800008)
	310
Access	R/W

This is a general purpose 32-bit register that can be freely read/written by both CPUs. It is usually set by the Starbuck and read by the Espresso, though this is not a requirement.

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LT_IPC_ARMCTRL (0x0d80000c)
	31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16
Access	U
Field
	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Access	U										R/W	R/W	R/W	R/Z	R/Z	R/W
Field											IX2	IX1	Y2	X1	X2	Y1

Field	Description
Y1	Read/write flag Y1
X2	Read flag X2. To clear the flag, write 1 to this bit.
X1	Read flag X1. To clear the flag, write 1 to this bit.
Y2	Read/write flag Y2
IX1	If set, flag X1 generates Latte interrupt #31
IX2	If set, flag X2 generates Latte interrupt #31

This register exposes the Starbuck side of the IPC control. Flags Y1 and Y2 may be freely set/cleared. Flags X1 and X2 can be read and cleared (by writing one), and can optionally generate IRQ #31. The Espresso does not have any kind of access to this register.