Project

General

Profile

BCM4751 » History » Version 20

Denis 'GNUtoo' Carikli, 12/04/2012 02:23 PM

1 1 Paul Kocialkowski
h1. Broadcom4751GPS
2
3 9 Paul Kocialkowski
h2. Factory image files
4 1 Paul Kocialkowski
5 2 Paul Kocialkowski
The non-free files holding the GPS infos/code are the following:
6 1 Paul Kocialkowski
<pre>
7
/system/vendor/bin/gpsd
8
/system/vendor/lib/hw/gps.s5pc110.so
9
/system/vendor/etc/gps.xml
10
/system/etc/gps.conf
11
</pre>
12
13 9 Paul Kocialkowski
h3. gps.xml parameters 
14
15
We have tried to change some parameters in gps.xml to see how it behaves:
16
17
|_. Parameter |_. Original |_. Changed to |_. Result |
18
| acPortName | /dev/s3c2410_serial1 | /dev/s3c2410_serial42 | The chip wasn't "booted" |
19
| gpioNStdbyPath | /sys/class/sec/gps/GPS_PWR_EN/value | /sys/class/sec/gps/GPS_PWR_EN/value2 | The chip was booted |
20
| gpioNResetPath | /sys/class/sec/gps/GPS_nRST/value | /sys/class/sec/gps/GPS_nRST/value2 | The chip was booted |
21
22
After all, it seems that when the gpsd binary is running without the gps.s5pc110.so library, the chip isn't started (our test utility doesn't work) whereas when the library is running and connects to the socket when it is created by starting gpsd, the chip is booted. 
23
24
gps.s5pc110.so will actually order bootup via the socket, when the gps is requested by the Android framework. When it's not used anymore, it will request poweroff as well.
25
26 1 Paul Kocialkowski
h2. Protocol
27
28 9 Paul Kocialkowski
According to the logs obtained from gpsd, the chip seems to be using the MEIF protocol at first, then a patch is sent and it starts using another protocol, which doesn't seem related to MEIF according to the logs (there are basically no more references to MEIF after uploading the patch). However, as we have no information about what MEIF is (it's a binary proprietary undocumented protocol), these are just guesses.
29
We decided to implement the first protocol under the name MEIF, but it could also be some sort of BCM4751-specific bootloader protocol that is in charge of making the patch upload.
30 1 Paul Kocialkowski
31 9 Paul Kocialkowski
The GPSD component is in charge of translating the second protocl to standard NMEA that is sent to the gps.s5pc110.so lib via the /dev/socket/gps Unix socket, created by GPSD.
32 1 Paul Kocialkowski
33 9 Paul Kocialkowski
h2. Devices
34 1 Paul Kocialkowski
35 9 Paul Kocialkowski
Here is a list of the devices that are known to use the BCM4751 chip:
36 1 Paul Kocialkowski
37 9 Paul Kocialkowski
|_. Device |_. Vendor |_. BCM4751 revision |
38 16 Denis 'GNUtoo' Carikli
| Nexus S | Google/Samsung | 4751A1 or 4751A2 |
39 9 Paul Kocialkowski
| Galaxy S I9000 | Samsung | 4751A2 |
40
| Galaxy Tab P1000 | Samsung | ? |
41 14 Paul Kocialkowski
| Galaxy Tab 8.9 P7300/P7310 | Samsung | 4751A2 |
42 9 Paul Kocialkowski
| Nexus 7 | Google/Asus | ? |
43 1 Paul Kocialkowski
44 15 Paul Kocialkowski
The bCM4751 chip exists under the following revisions: 4751A0, 4751A1, 4751A2, 47511A0
45
46 9 Paul Kocialkowski
h2. Free software implementation
47 1 Paul Kocialkowski
48 9 Paul Kocialkowski
On January 2012, the work to write a free software implementation that could handle the BCM4751 chip was started.
49
The main target is the Nexus S, even though it should work with few changes on other BCM4751 devices.
50 1 Paul Kocialkowski
51 9 Paul Kocialkowski
The code source is available at: https://gitorious.org/replicant/crespo-gps-utils
52 1 Paul Kocialkowski
53 9 Paul Kocialkowski
h3. Current status
54 1 Paul Kocialkowski
55 9 Paul Kocialkowski
|_. Part |_. Status |_. Comments |
56
| Serial setup | "DONE":https://gitorious.org/replicant/crespo-gps-utils/commit/e4f94e901b9b4c5fef5642ad9580863fc2bfe336 | Magic is: @termios.c_cflag = 0x800018b2;@ |
57
| MEIF parsing | "DONE":https://gitorious.org/replicant/crespo-gps-utils/commit/927c1c92dd092cec8c56351bf663101183f19076 | |
58
| MEIF dispatch | "DONE":https://gitorious.org/replicant/crespo-gps-utils/commit/f952dde8f3a29634be1c8fa19b8eed367c1ad878 | |
59
| MEIF patch upload | "DONE":https://gitorious.org/replicant/crespo-gps-utils/commit/9a5827778189b7e0f91879430a4e160567ee6bbd | Nexus S and Galaxy S patches differ |
60 1 Paul Kocialkowski
61 9 Paul Kocialkowski
h3. Utilities
62
63
|_. Name |_. Task |_. Arguments |
64
| bcm4751_gpsd | Main utility, boots the chip, send the patch, switch protocol | None |
65
| bcm4751_test | Deprecated utility, can be used for poweroff | @stop@: poweroff the chip |
66
| bcm4751_hal | Acts as the framework: permits to trace gps.s5pc110.so | None |
67
| bcm4751_daemon | Acts as (a fake) gpsd to the lib | None |
68
| bcm4751_lib | Acts as (a fake) lib to gpsd | None |
69
70
h3. BCM4751 gpsd
71
72
This is where MEIF is implemented. It currently does the following:
73
* Serial setup
74
* Autobaud
75
* MEIF reader loop
76
* MEIF parsing
77
* MEIF dispatch
78
* MEIF patch upload
79
* Protocol switch (sends unknown bytes in the second protocol to get a response)
80
* Response dump
81
82
Sample output log:
83 1 Paul Kocialkowski
<pre>
84 9 Paul Kocialkowski
Turning the GPS on...
85
Opening the GPS serial...
86
Sending autobaud...
87
Read 17 bytes
88
Read 32 bytes
89
MEIF message: MEIF_STATE_REPORT_MSG with 18 bytes of data:
90
[0000]   01 00 00 00 01 00 00 00   00 00 00 00 00 00 00 00   ........ ........
91
[0010]   1A 00                                               ..
92
Got a STATE_REPORT message
93 1 Paul Kocialkowski
94 9 Paul Kocialkowski
Read 23 bytes
95
Read 32 bytes
96
Read 16 bytes
97
Read 7 bytes
98
MEIF message: MEIF_CONFIG_VALUES_MSG with 70 bytes of data:
99
[0000]   02 00 01 00 01 00 40 00   01 00 02 00 00 00 00 00   ........ ........
100
[0010]   01 00 02 00 00 00 00 00   00 00 06 00 81 11 00 09   ........ ........
101
[0020]   07 07 D9 07 42 52 4F 41   44 43 4F 4D 00 00 00 00   ....BROA DCOM....
102
[0030]   00 00 00 00 34 37 35 31   41 31 00 00 00 00 00 00   ....4751 A1......
103
[0040]   00 00 00 00 B3 05                                   ......
104
Got config values:
105
	vendor: BROADCOM
106
	product: 4751A1
107
108
Sending the first part of the patch...
109
Sending 2054 bytes!
110
MEIF message: MEIF_SEND_PATCH_MSG with 2046 bytes of data:
111
112
Read 14 bytes
113
MEIF message: MEIF_NACK_MSG with 6 bytes of data:
114
[0000]   03 00 03 00 0F 00                                   ......
115
Got a NACK message
116
Reason is: MEIF_NACK_GARBAGE_RECEIVED
117
118
Read 12 bytes
119
MEIF message: MEIF_ACK_MSG with 4 bytes of data:
120
[0000]   04 01 0B 00                                         ....
121
Got an ACK message
122
123
Sending the second part of the patch...
124
Sending 706 bytes!
125
MEIF message: MEIF_SEND_PATCH_MSG with 698 bytes of data:
126
127
Read 12 bytes
128
MEIF message: MEIF_ACK_MSG with 4 bytes of data:
129
[0000]   05 02 0D 00                                         ....
130
Got an ACK message
131
132
Ready to switch protocol!
133
Sending unknown bytes!
134
Read 12 bytes:
135
[0000]   FE 00 FD 40 00 00 F1 B1   12 20 67 FC               ........ ..g.
136
</pre>
137 1 Paul Kocialkowski
138 10 Paul Kocialkowski
h3. BCM4751 patch
139
140
In order to use the same protocol as the non-free gpsd, a patch needs to be sent. It is hardcoded in the non-free gpsd binary.
141
Note that we don't know what that patch exactly is nor what it does. In any case, it must be considered as the propriety of Broadcom (or Samsung maybe) and falls under the non-free gpsd license.
142
143
Here are notes on how to extract the patch from various non-free gpsd binaries:
144 13 Paul Kocialkowski
|_. Device |_. Source |_. GPSD MD5 |_. Offset |_. Length |_. dd command |
145
| Nexus S | CM 9.0.0 | 4a6c0027e530b5b8a346153a355ef8e3 | 0x15DDEA | 2738 bytes | dd skip=1433066 count=2738 if=gpsd of=bcm4751a1.fw bs=1 |
146
| Galaxy S | CM 9.1.0 | 4a6c0027e530b5b8a346153a355ef8e3 | 0x15E89E | 6406 bytes | dd skip=1435806 count=6406 if=gpsd of=bcm4751a2.fw bs=1 |
147 10 Paul Kocialkowski
148 13 Paul Kocialkowski
The @bcm4751_gpsd@ utility will attempt to read the patch from @/data/bcm4751a1.fw@ or @/data/bcm4751a2.fw@
149 10 Paul Kocialkowski
150 18 Denis 'GNUtoo' Carikli
h4. Post protocol switching
151
152 20 Denis 'GNUtoo' Carikli
Sending this string:
153
"\xfe\x00\xfd\x6f\x3a\x01\x00\x00\x00\x00\x34\xfc"
154
many times makes some other string appear on the serial port...
155 17 Denis 'GNUtoo' Carikli
<pre>
156 20 Denis 'GNUtoo' Carikli
fe 00 fd 0f ff 07 06 00 00 01 54 fc
157
fe 00 fd 0f ff 08 06 00 00 01 1c fc
158
</pre>
159
Here's the decoding of the first bytes:
160
<pre>
161 17 Denis 'GNUtoo' Carikli
ff00 = 8bytes
162
fe00 = 12bytes
163
fe01 = 16bytes
164
fe02 = 20bytes
165
fe03 = 24bytes
166
fe04 = 28bytes
167
fe05 = 32bytes
168
fe06 = 36bytes
169
fe07 = 40bytes
170
</pre>
171 20 Denis 'GNUtoo' Carikli
172
fc seem an end marker and 54/c1 a checksum....