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TimeSerialPort » History » Version 2

laforge, 02/19/2016 10:49 PM
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h1. The Time Serial Port (TSP
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The TSP is a synchronous real-time control interface in TI GSM chipsets.
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The Digital Baseband (DBB) chip normally drives the TSP. The DBB has a special integrated peripheral unit called [[TimeProcessingUnit|TPU]] to drive the TSP.
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The Baseband Codec and Transceiver chips are driven by the TSP (slaves)
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h2. Rationale
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GSM is a synchronous TDMA system. As such, all clocks are related to each other, and all events driven synchronous to the master clock.
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The carrier clock determines the bit clock, which in turn determines the frame clock.
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When e.g. sending a GSM burst, a number of events have to happen synchronously to ensure transmitting it at the right instance in the TMDA sequence:
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* switching the RF-PA on
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* ramping up the power envelope
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* calibrating the DC offset
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* switching the MEMS antenna switch to the correct band
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* starting the transmit of the actual burst data
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To synchronize those events, and to schedule them in sequence before the burst is transmitted, the TSP is used.
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h2. Parallel vs. Serial
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In early GSM transceivers, all the events could be driven by dedicated electrical lines from the TPU.
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However, in multi-band configurations and with integrated baseband codec circuits, it made more sense to
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have a serial interface to limit the number of signals that need to be routed between components.
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h2. TSP Signals
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In the Calypso/Iota/Rita based modem designs, the TSP is only used uni-directional, i.e. from the DBB to the peripherals.
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Thus, only the following signals are needed:
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* TEN (TSP Enable), one for each peripheral
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* CLK13M - the 13MHz clocl that runs everywhere
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* TDX (TSP Data Tx) (used bi-directional for RF6151C)
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