|
USB only guarantees 500mA, this is why the USB charge circuitry doesn't allow the device to be on during USB charging, it is only sufficient current to slowly charge the battery, not enough for full speed charging, or device operation. From glancing over the datasheets for the power hardware in the iRiver, it looks like it probably uses a different charge mode when charging from USB to avoid damage.
It may be possible for rockbox to have a setting where it would assume that the AC adapter is only going to supply USB current levels to allow charging from these low current supplies, or to have a setting for high power USB charging / operation.
The Sony PSP charge circuitry for USB actually offers two modes, one for slow USB charge and one for full speed USB charge. Most powered USB hubs will supply a total of 2A split between their ports (shared) and the PSP can take advantage of this by sucking more than 500mA to charge just as fast as an AC adapter. This does often disable any other devices connected to the hub, and if you use that mode on some USB ports, it can fry the port.
|