UPAMD,
Here is the working version of the requested power message.
From: Bob Davis [mailto:bobd@xxxxxxxx]
Sent: Friday, May 20, 2011 9:31 AM
To: 'upamd-power@xxxxxxxx'
Cc: 'Bob Davis'
Subject: Requested power message
Power Group,
Here is a fixed up proposal for the requested power message with the minimum power back in the message. The intent is that when the source receives the requested power message, it can set the low and high bounds on the expected power usage. To make room, I changed the stored available power value to be only the most significant byte as we are more interested in large numbers here. Comments on the Device Status list are solicited.
This change should allow the flow diagrams that Edgar presented to work with a limited number of transitions. Of course sinks can always behave badly. Initial negotiations for power should only take two message interchanges.
Byte0 = Maximum Power: This would be the maximum power that this device would ever request. The source could permanently allocate any available power above this value to other uses/ports, such as filling the onboard battery backup system, if any.
Byte1 = Current Requested Power: This is the current power request and should be between the Maximum Power and the Minimum Power Required. This is what is being asked for. Current Requested Power of 1 was to indicate a sleep condition, and a Current Request Power of 0 is to request turn off.
Byte2 = Minimum Power Required: This would be the minimum power that would let the sink operated as designed but possible at a slower speed etc. If this much power is not available from the source, the power negotiation should fail with insufficient power. This number may change due to conditions in the sink, such as full batteries or unused peripheral that will not need power.
Byte3 = Minimum Required Voltage: Lowest voltage that the sink can operate with. This would be defaulted to 21V(at source) under normal circumstances. Printers and higher power systems may not operate at this nominal level because of power requirements and the inability of the sink to boost the voltage.
Byte4 = Current Voltage Request: Nominal value would be 21V(at source) but could also be another value depending on the load, above or below the nominal value. This is expected to accommodate the printers ~35V or higher power systems ~42-60V. This possibly could accommodate lower voltage systems such as 13.75V vehicle or fixed 12V systems if, and only if, the source has this flexibility. Inexpensive fixed sources would reject anything other than the nominal value. Negative acknowledge is used by the source with a reassertion of the available voltage in the Available Power Message.
Byte5 = Stored Available Watt-hours: This is the high byte of the 16bit value of power currently stored in the sink, in watt hours, that may be available. If no power is stored this is defaulted to 0. This value is in increments of 256watt-hours. The purpose is to keep the Source informed of the power available to the sink, and to the source if the port is bidirectional, as an indicator of the power need in a restricted power condition. If the sink chooses not to report stored power the value is set to 0.
Byte6 = Fill State and Device Status:
Fill state is a 3 bit value to indicate the current state of the sink on board battery system, if any. The report is in 1/8 of battery full condition, 000 – empty and 111 is full. Purpose is to keep the source informed of the state of the power system in the sink. If the battery in the sink is full, the sink may reduce its Minimum Required Power value as it could survive on internal sources, or let the source know if there is a high priority demand elsewhere in the system, this sink can survive on available resources. Non-battery systems set this value to 000. Full battery system would be expected to lower their Device Power Priority level.
Device status is a 32 condition status message. Most Values to be determined.
00000 = Healthy and normal.
XXXXX = TBD - overheated, full, battery failure, sleeping, message ready or message needed.
Recommendations welcome – need a standard set of conditions.
11111 = Critical failure – no longer functional
Byte7 = Request command/message number: This provide the mechanism for the sink to request information from the source. It may request any message available or request/issue a command to be defined as the standard is developed. If the requested message or command is not available the source will return a negative acknowledge. As this is sent with each message a default value for none required could be all 0 or all 1.
A minimum sink could probably set the max, min, and requested power to the same value for simplicity. Not friendly, but legal.
Comments are appreciated and invited.. How do we make this better?
Respectfully;
Bob Davis
Summit Computer Systems, Inc.
bobd@xxxxxxxx
408.857.1273