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Iomega G2 MC68HC908QY4 Support Notes
October 2006
The Iomega G2 Version 3.x and 5.x boards have a secondary microcontroller
aboard, a Freescale MC68HC908QY4. This microcontroller is connected to the
board's LED, fan, digital thermometer, power switch, and main processor, the
MPC8241. The connection to the main processor is through the 8241's second
UART and possibly its reset lines.
The microcontroller can perform the following functions:
o The LED can be set to off, blue, red, blue flash, red flash,
alternate (blue->red->blue) and some boards alternate3
(blue->blue->blue->red->red->red). The flash and alernate rates
can be be set. Alternate3 rate is fixed.
o Fan can be set to on or auto. Auto mode is a thermostat function
that turns the fan on and off based on two temprature settings:
Fan Temp High and Fan Temp Low.
o The system can be reset, causing a MPC8241 reset, or stopped,
causing a full power down.
o The microcontroller can detect if the soft power switch has been
activated. There appears to a 20s delay after the power switch
has been depressed before the microcontroller causes an actual
power off. This event can be detected by polling the
microcontroller.
The running system communicates with microcontroller and ultimately controls
the devices connected to it via the MPC8241's second UART. The connection
settings are: 9600,8,n,1. The serial protocol is very simple, an alternating
send and receive of data packets. Communication is done in 8 byte data packets
and is initiated by the host processor. Once the host processor has sent 8
bytes, the microcontroller responds with 8 bytes. The packet contains bytes
that can affect the state of the power, led and fan. It also contains bits
reflecting external soft power events. Both packets sent and received follow
the same structure.
The 8 bytes are decoded as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Power | LED | LED | Fan |
| State | State | Flash Rate | State |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Fan High Temp | Fan Low Temp | | |
| ON | OFF | ID | CheckSum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Hex Ascii Comments
--- ----- --------------------------------------------------
Power State:
0x62 b Running, nominal running state
0x63 c Stop, power down immediately (ID == HOST) OR
Stop, the power switch has been activated, stop in 20s
(ID == CONTROLLERxx) OR
Stop, the host has advised Stop
(ID == CONTROLLERxx)
0x64 d Advise Stop, the host is annoucing its intention
to stop (ID == HOST)
0x65 e Restart, restart immediately (ID == HOST) OR
Restart, the host has advised Restart
(ID == CONTROLLERxx)
0x66 f Advise Restart, the host is annoucing its intention
to restart (ID == HOST)
0x67 g Reset, reset immediately (ID == HOST) OR
Reset, the host has advised Reset
(ID == CONTROLLERxx)
0x68 h Advise Reset, the host is annoucing its intention
to reset (ID == HOST)
Except for Running, the Power states are grouped in pairs: Advise [state] and
[state], where state can be: Stop, Restart, or Reset. The Advise state lets
the controller know that there is an intention to either stop, restart or
reset the board. The controller responds by moving to that state and setting
the LED to redflash, but it does not enact the power change. Instead it waits
for the host to issue the actual state before performing the power commands.
For example, assume the microcontroller is reporting the power state to be
[Running, LED Blue]. After the host issues a Advise Stop, the microcontroller
reports [Stop, LED Redflash] and then waits, indefinitely. The Host then
issues a Stop, the microcontroller immediately turns the power off.
There is nothing in the protocol that requires the Advise [state] packets. The
Host can issue a Stop, Restart, or Reset directly from the Running state and
the microcontroller will immediately enact the change.
There is nothing in the protocol that forbids moving back to Running from the
Stop, Restart or Reset states, i.e. undoing an Advise [state] packet.
The exception to that rule is in the Stop state. The Stop state can be reached
by either issuing a Advise Stop or from a softpower switch activation (someone
hits the power switch). If the latter, then a request to move to any other
state is ignored and the power will go off in approximately 20s.
NOTE 1: There does not appear to be any difference in processing the Restart
and Reset state changes. They both deliver a system restart.
NOTE 2: Obvious absence of an 'a' state. Both the LED and Fan controls use 'a'
as a state, but Power starts with 'b'. No evidence has shown 'a' to be a
valid state.
LED State:
0x61 a Off
0x62 b Blue
0x63 c Red
0x64 d Blue Flash
0x65 e Red Flash
0x66 f Alternate1 Blue/Red
0x67 g Alternate3 3 Blue/3 Red (only on version 5.x boards)
LED States are self explanatory with one exception. Although state 'g' or
Alternate3 has been observed, it only seems to function on IOMEGA G2 Version
5.x boards and does not respond to rate changes.
LED Flash Rate:
The flash rate seems to be 1/x seconds on, then 1/x seconds off. So one cycle
of off and on at an LED Flash rate of 1 is almost 2s. The value spans 8 bits
but functionally 0 is off and 36-40 is on. Testing has shown an oddity, the
value 35 is rejected by the microcontroller software and is not set.
Fan State:
0x61 a Auto thermostat function
0x62 b On always on
Fan High Temp:
High Temp is the temprature in Celsius where the fan is be turned on.
Fan Low Temp:
Low Temp is the temprature in Celsius where the fan is be turned off.
ID:
The real purpose of this field is not known. It is known that it is a constant
depending upon the direction of the packets and the board rev. It has been
designated ID as a place holder but it could as easily be defined as version
or it may be something else entirely.
0x00 DC2 CONTROLLER00
IOMEGA G2 Version 5.x Controller ID (recv'd packets)
0x07 BEL HOST (sent packets)
0x12 DC2 CONTROLLER12
IOMEGA G2 Version 3.x Controller ID (recv'd packets)
Checksum:
The check sum is an 8 bit sum of the first 7 bytes with the most significant
bit cleared.
Sum = ((b1 + b2 + b3 +b4 +b5 +b6 + b7) & 0x7f)
The bytes and their meanings were determined by watching the serial port
chatter during specific events such as LED Blue, LED Red, Fan ON, etc. So only
events observed have been decoded. Although all the significant events were
observed and decoded, there are some holes in the understanding of the
protocol.
There is one special packet that causes the microcontroller to reset. This
packet is:
0x23696f6d 0x65676115
(or as a string "#iomega\025")
The resulting packet from the microcontroller is:
0x62000000 0x00000062
Testing also yielded that a null packet will cause the microcontroller to
feed back the current state. So this packet:
0x00000000 0x00000000
will yield something like this (this is the default state):
0x62620a61 0x322d1220
The default state when the board powers on is:
State: Run
LED: Red
LED Rate: 10
Fan: On
Fan Temp High: 50C
Fan Temp Low: 45C
Below is some of the data collected while watching the serial port chatter:
w: 0x23696f6d 0x65676115 #iomega\025
r: 0x62000000 0x00000062 b\0\0\0\0\0\0b
w: 0x62630a61 0x322d0716 bc\na2-\7\26 red state
r: 0x62630a61 0x322d1221 bc\na2-\22!
w: 0x62641161 0x322d071e bd\21a2-\7\36 blue flash
r: 0x62641161 0x322d1229 bd\21a2-\22)
w: 0x62641161 0x322d071e bd\21a2-\7\36 blue flash
LED ok
w: 0x62620a61 0x322d0715 bb\na2-\7\25
r: 0x62630a61 0x322d1220 bb\na2-\22
LED alt
w: 0x626f0a61 0x322d0719 bf\na2-\7\31
r: 0x626f0a61 0x322d1224 bf\na2-\22$
reset
w: 0x68620a61 0x322d071b hb\na2-\7\33 reset
r: 0x67620a61 0x322d0013 gb\na2-\0\23 resetting
restart
w: 0x66620a61 0x322d0719 fb\na2-\7\31 restart
r: 0x65620a61 0x322d1223 eb\na2-\22# restarting
shutdown
w: 0x64620a61 0x322d0717 db\na2-\7\27 shutdown
r: 0x63620a61 0x322d1221 cb\na2-\22! power shutting down
soft Power
r: 0x63620a61 0x322d000f cb\na2-\0\17 power shutting down
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