Hammerhead/Integrators
From Openmoko
The integrators are perhaps the key to the hammerhead chip.
The GPS signal comprises several levels. First there is the carrier, which is multiplied by the 1024 element long spreading code, at a chip rate of 1.024Mhz, leading to a input bit rate of 1Khz.
Then the navigation messages are modulated onto these input bits at a rate of 50Hz, so a navigation bit comprises 20 input bits.
There must be several integrators to track the GPS signal, while meeting the observed packet transfer statistics.
As there are no periodic transfers at 1Khz from each satellite, or even 50Hz, it must somehow store the navigation message bits and send them on when requested.
Exactly how 'cooked' this is is an interesting question.
