Cmep

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This processor is hypothesized to perform most of the cryptography tasks including storing and handing of keys. There is little information about it though. The F00D Processor (named after the e_machine field of the ELF headers) is likely a custom Toshiba MeP core.

Communication

Communication seems to go through some sort of FIFO register.

Write

To write, put the double word into 0xE0000010. Next read 0xE0000010 until it returns 0, which indicates the data was read by the F00D processor.

Read

To read, get a double word from 0xE0000000. If it returns 0, no data is available. Otherwise, acknowledge that the data has been read by putting the same data into 0xE0000000.

Extra ports

In addition to the 0xE0000000 and 0xE0000010, the communication with F00D seems to happen with other ports too.

Port Read Write Used by
0xE0000004 YES ? SMC 0x12d, 0x136, 0x137, 0x13B Interrupt 0xC8
0xE0000008 YES ? SMC 0x12d, 0x136, 0x137, 0x13B Interrupt 0xC8
0xE000000C YES ? SMC 0x12d, 0x136, 0x137, 0x13B Interrupt 0xC8
0xE0000014 YES YES SMC 0x12d, 0x133, 0x134, 0x13B Interrupt 0xC8
0xE0000018 YES YES SMC 0x12d, 0x133, 0x134, 0x13B Interrupt 0xC8
0xE000001C YES YES SMC 0x12d, 0x133, 0x134, 0x13B Interrupt 0xC8
0xE0000054 ? YES SMC 0x12d, 0x135, 0x13B, Interrupt 0xC8
0xE0000058 ? YES SMC 0x12d, 0x135, 0x13B, Interrupt 0xC8
0xE000005C ? YES SMC 0x12d, 0x135, 0x13B, Interrupt 0xC8
0xE0010000 YES YES ?
0xE0010004 YES ? ?

Protocol

A 32-bit command buffer is defined below. The command is sent to the F00D processor with the method listed above.

Bit End Bit Start Name Description
31 23 ? ?
22 19 flag? b1010, b0010, b0001
18 13 ? Always 0
12 8 ID Command ID
7 1 ? Always 0
0 0 Valid Set 1 to indicate command is valid

Command ID

There are a total of 14 commands. Below are notes on different commands.

0x0

Set the 0x100 sized shared buffer. First the physical address of the buffer is written to 0xE0000010 and then command 0x0 is written.

0x1

May be used to reset F00D processor.

0x2

Load sm.

Offset Size Description
0x0 0x4 num_paddrs
0x4 0x4 paddr_list for sm elf
0x8 0x4 buf_0x40: some 0x40 buffer
0xC 0x4 ctx_0x4
0x10 0x4 ctx_0x8
0x14 0x4 ctx_0xC
0x1C 0x4 field_60: system version (2)
0x20 0x4 partition ID

0x3

Load previously suspended sm

Offset Size Description
0x0 0x4 num_paddrs
0x4 0x4 paddr_list for suspend buffer
0x8 0x4 buf_0x40: some 0x40 buffer
0xC 0x4 delayed_cmd

0x4

Suspend current sm

Offset Size Description
0x0 0x4 num_paddrs
0x4 0x4 paddr_list for suspend buffer
0x8 0x4 buf_0x40: some 0x40 buffer
0xC 0x4 delayed_cmd

0x5

Kill current sm

0x6

?

0x7

Unused.

0x8

Unused.

0x9

Set a 0x80 sized shared buffer.

Offset Size Description
0x0 0x4 paddr
0x4 0x4 length

0xA

Set the SCE encrypted revocation list.

Offset Size Description
0x0 0x4 num_paddrs
0x4 0x4 paddr_list for revocation list

0xB

0xC

0xD

0xE

0xF

0x10

Memory

kprx_auth_sm.self is allowed access to 0x1F000000, 0x1F840000, 0x20000000, and 0x40300000. The address checks is likely done in software. F00D has it's own private 128KB memory from 0x00800000 to 0x00820000. F00D SELFs are typically loaded to 0x0080B000.