88W8388

The 88W8388 is a wireless controller chip made by Marvell. It is part of the unliberated Libertas chip family. Beyond this page, it is rather undocumented. In the XO, it is installed on the Marvell Wireless Module.

The problem is bug #46 and bug #429 in trac.

Close-up pictures of the XO's wireless module and the similar Xbox360 wireless device may be of interest. The XO uses an 88W8015 radio chip with a 48 MHz crystal, while the Xbox360 uses an 88W8030 chip with a 40 MHz crystal. Both use the 88W8388 processor chip.

Debugging

Your options are emulation, USB, serial, the radio itself, blinking LEDs, maybe some random GPIOs, and JTAG.

For now, JTAG is the best way to debug your new Open Source firmware. JTAG is also useful for reverse engineering. You will need something like one of these:

• $52 ARM-USB-TINY (2.0v to 5.0v)
• $72 ARM-USB-OCD (2.0v to 5.0v, plus serial and power)
• €129 JTAGkey (1.4v to 5.0v)
• €29 JTAGkey-Tiny (2.8v to 5.0v)
• free: some horrid hack involving spare parts and your parallel port

Notice the CN1 connector (Hirose FH12 0.5mm pitch 10 pin) pads on the lower-right part of the backside of the OLPC XO motherboard. There are identical pads on the Xbox360 wireless device. These pads function as follows:

 1  35  2.92  inside  TRSTn
 2  36  3.13  outside IDI
 3  37  2.94  inside  TSM_ARM
 4  38  2.92  inside  TCK
 5  39  3.33  outside RTCK
 6  40  2.10  outside TDO
 7  41  2.92  resetn  SRSTn
 8      0.00  gnd
 9      nc?   nc?
10      3.33  vcc3.3

That is the pad number, "pin" of the OLPC wlan module, measured voltage, notes, and usage. Pads 1 to 7 are connected to "pins" 35 to 41 on the wireless module, which are easier to solder wires to.

Gross memory map

00000000 0000ffff RAM (code) repeating every 64 KiB
04000000 04001fff stack
80000000 8000ffff IO memory
90000000 9000ffff IO memory
c0000000 c0027fff RAM (code, data, bss, heap) repeating every 256 KiB
fff00000 ffffffff boot1 ROM, 8 repetitions of 128 KiB containing ThreadX

0xffff0000 is where code execution starts. We call this the boot1 code. It contains ThreadX, but does not normally run ThreadX. Normally, boot1 copies boot2 from an SPI EEPROM to 0x00000000 and enters that at address 0.

boot2 is about 10240 bytes. It self-relocates from 0x00000000 to 0xc00xxxxx (near the end), then loads the main firmware. On 88W8385 hardware, boot1 is in a 4096-byte area at 0xc0000000 and the main firmware loads at 0xc0001000.

The main firmware can come from USB or from SPI EEPROM. It loads into both the 0x0000xxxx and 0xc00xxxxx regions, then starts at a specified address which is normally 0x00000000. 88W8388 firmware starts at 0xc0000000 for the high portion, while 88W8385 firmware loads at 0xc0001000 to avoid clobbering boot2.

CPU

This is a 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 wikis (Mediawiki without pictures, MoinMoin with pictures), 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, the entry point address (normally 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.. Use extract.c to extract firmware files from driver files.

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.

Gross EEPROM map

0000 027f   config data of some sort, 640 bytes
0280 033f   config data of some sort, 192 bytes (all 1 bits on older hardware)
0340 0fff   all 1 bits
1000 37ff   the Boot2 code, 10240 bytes
3800 3fff   all 1 bits

Use ethtool to read it out in 16-byte chunks. You can grab the whole thing in about 18 seconds.

for i in 0 1 2 3 ; do
  for j in 0 1 2 3 4 5 6 7 8 9 a b c d e f ; do
    for k in 0 1 2 3 4 5 6 7 8 9 a b c d e f ; do
      ethtool -e msh0 offset $((0x$i$j$k*16)) length 16
    done
  done
done

Munge with normal tools (sed,awk,perl,colrm,xxd,grep) as needed to produce a binary file.

Storage in the EEPROM is byte-swapped. Most boot2 files are also byte-swapped.

Config data in the EEPROM

0000 EEPROM magic 0x38333058 ("830X")
0004 boot2 length
0008 boot2 eeprom offset
000C MAC address, followed by 0x02 0x00
0014 a length
0018 an eeprom offset
001c a destination pointer (in RAM?)
0030 usbPID:usbVID (if 0xffffffff, then 0x31081286 is used instead)

As with all EEPROM stuff, this is byte swapped.

IO memory

0x80002000 bits 5,6,7 relate to pins on the hardware package and are used by the boot1 ROM to decide where the chip should read boot2 from. This register contains 0x004269aa on the Xbox360 and 0x004269ba on a B1 XO. Masked with 0xe0 (for bits 5,6,7) that is 0xa0. Values of 0xa0 and 0xc0 mean that boot2 is loaded from an SPI EEPROM. Values of 0xe0 and 0x80 mean that boot2 comes from SDIO (with Libertas being on the SDIO device, not being a host). A value of 0x00 means that boot2 is received via xmodem protocol at 38400 baud. A value of 0x40 means to boot ThreadX from the ROM. Values of 0x20 and 0x60 will loop.

0x80002000 bit 4 is set if 2-byte EEPROM addresses should be used, but cleared if 3-byte addresses should be used.

0x80002000 bits 2,1,0 mean CompactFlash (5), SDIO (6), or SPI (7).

0x80002018 contains a hardware type code. Shift right by 16 bits then mask with 0x1f to get it. For values of 7 or 18, mmio1 is 0x90000000 and mmio2 is 0x90000800. For other values, mmio1 is 0x8000c000 and mmio2 is 0x8000c100. The content of 0x80002018 on an Xbox360 or a B1 XO is 0x00070003, leading to a value of 7. Thus mmio1 is at 0x90000000 and mmio2 is at 0x9000800. Bits 16 to 23 (byte at 0x00ff0000) of this register form the XX part of "802.11 SDIO ID: XX", which is provided to identify the device when it is on SDIO.

0x90000140, possibly defined as mmio1+0x140, is a 16550 UART serial port that is the default use for some of the GPIO pins. The registers, though 8-bit, are in 32-bit locations. Thus 0x90000140 (register 0) is transmit/receive, 0x9000014c (register 3) is config, 0x90000154 (register 5) is status, and so on.

mmio1+0x200 is GPIO output enable X, 2 bits per GPIO. When a field is set to 1, output works. Values of 0,2,3 (typically 0) choose stuff like the 16550 UART, transmit/receive blinks, etc. Since this MMIO area is only 16 bits wide, this register requires two addresses. The low 8 GPIO lines are here, and the high 8 are at mmio1+0x204.

mmio1+0x204 is GPIO output enable X, part 2. See mmio1+0x200 for details.

mmio1+0x208 is GPIO output enable Y, or GPIO input enable. It is 1 bit per GPIO line. Setting a bit causes the GPIO to be used for input. Clearing a bit causes the GPIO to be used for output.

mmio1+0x20c is GPIO output. The two low bits, GPIO0 and GPIO1, are normally attached to LEDs. On the Xbox360 these are inverted logic, with bit 0 being !red and bit 1 being !green. On the B1 XO this is GPIO1 being !ant(left) and GPIO12 being !act(right)

mmio1+0x210 is GPIO input.

An input GPIO10 of 0 tells the XO's boot2 code to boot from eeprom. (read mmio1+0x210, then mask with 0x400) It is likely that this distinguishes a laptop from an Active Antenna.

90000000 w8 
90000004 w8 
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. There is also a list of corrections for that document.

DMA

The firmware's view of DMA involves something like this:

struct dmainfo {
    unsigned bytes;
    char *src;
    char *dst;
    struct dmainfo *next; // NULL for last block
}