88W8388
The 88W8388 is a wireless controller chip made by Marvell. It is part of the unliberated Libertas chip family. Outside of this page, it is undocumented.
Critical TODO items
- Find any JTAG, serial port, or audio (supposedly!) connections
- Dump out the ROM
- Get ARM cross-compiler stuff into Fedora, or at least into the OLPC RPM repository. Building these tools on an XO is impractical.
Gross memory map
00000000 0000ffff code, part 1 04000000 04001fff stack 10000000 1fffffff nothing, but add-on flash or RAM would go here 80000000 8000ffff IO memory 90000000 9000ffff IO memory c0000000 c000ffff code, part 2 c0010000 c0027fff heap and bss ffff0000 ffffffff boot code
CPU
This is an little-endian ARM chip. "xscale" appears to be a good match. Mostly it is used to run thumb code, but some regular ARM code is used as well. ARM code can be spotted in hex dumps because most instructions will start (4th byte in little-endian) with the hex digit "e".
According to the free60 project, there is an ARM946E-S core (as per the ARM Networking brochure) inside the 88W8388.
Note that objdump is completely unsuitable for disassembling this code. You need an interactive disassembler and/or one that traces code flow. Something like objdump will be unaware of the transitions between plain ARM code, thumb code, and data. It is normal for functions to be followed by constants; a good disassembler will match these up with the code instead of stupidly disassembling them.
A free (GPLed) option is to use adiss. Adiss can disassemble firmware blobs where code, thumb and data are intermixed. This isn't automatic like it would be with IDA Pro, but the level of effort is reasonable. Future revisions will make it easy to share notes (section markers, comments, etc.) without violating copyright. See the October 2007 announcement email for a usage example. Get it via subversion, see here.
Main firmware format
Firmware is a stream of packets like this.
le32 0x00000001 if data follows, else 0x00000004 le32 destination address le32 data length including final CRC, normally 0x200 bytes be32 header CRC (1st 12 bytes and 4 zero bytes) char[508] may be smaller for the last block be32 data CRC (the 508 bytes and 4 zero bytes)
Data length goes short at the end of a segment. After the very last block of the whole file, there is one special header. It has code 0x00000004, address zero, length zero, a header CRC, no data, and no data CRC.
Use bin2elf.c and elf2bin.c to convert firmware files to/from ELF..
CRC
polynomial 0x04c11db7 (common CRC32) initial remainder 0 no reflections no inversion at the end stored in big-endian format! on creation, include 4 trailing zero bytes nice property: the CRC of the data with following CRC will be zero
Boot firmware format
It's just 10240 bytes of byte-swapped code. This code, known as Boot2, is flashed into the Marvell chipset. It implements the USB interface required for loading the main firmware.
IO memory in the 9000xxxx area
90000000 w8 90000004 w8
At 90000200 and 90000204, we find a pair of 16-bit registers full of 2-bit fields. At 90000208 we find a 16-bit register full of 1-bit fields that match up with the 2-bit fields. This is two arrays, with the first being split because electrical engineers love to torture the software guys. Each array element appears to control a 256 MiB memory region, with a 1 bit in the 90000208 register being used to enable the cache. When such a bit is set, the corresponding 2-bit field in the 90000200 or 90000204 register should be set to 1. (values 0,2,3 are likely to be various cache policies like write-through)
90000200 r32 w16 w32 90000204 r32 w16 w32 90000208 r32 w16 w32 9000020c r32 w16 w32 90000214 r32 w32 90000218 ? 90000220 r32 w32 90000228 r32 w16 9000022c r32 w16 90000230 r32 w16 90000234 r32 w16 90000238 r32 w16 9000023c r32 w16 90000240 r32 w16 90000244 r32 w16 9000024c r32 w16 90000254 r32 w32
90000800 r16 90000804 r32 w32 r8 w8 90000806 r8 90000808 r32 r16 w16 9000080c r8 9000081c r8 poll until bits among 0xc3 are set 90000824 r32 w32 r8 w8 90000828 w32 w8
9000b010 w32 9000b014 w32 9000b018 w32 9000b024 w32 9000b028 w32 9000b02c w32 9000b030 w32 9000b034 w32 9000b038 w32 9000b03c w32 9000b040 w32
9000b100 r32 w32 9000b118 w32 9000b11c w32 9000b120 w32 9000b124 w32 9000b128 r32 9000b12c r32 9000b130 r32 9000b134 r32 a low bit we can poll for a change
Standard interface
The proprietary firmware implements an interface which the Linux driver uses. This interface is described in an old document attached to an email, and in a list of corrections.