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The Time Serial Port (TSP

The TSP is a synchronous real-time control interface in TI GSM chipsets.

The Digital Baseband (DBB) chip normally drives the TSP. The DBB has a special integrated peripheral unit called TPU to drive the TSP.

The Baseband Codec and Transceiver chips are driven by the TSP (slaves)

Rationale

GSM is a synchronous TDMA system. As such, all clocks are related to each other, and all events driven synchronous to the master clock.

The carrier clock determines the bit clock, which in turn determines the frame clock.

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:
  • switching the RF-PA on
  • ramping up the power envelope
  • calibrating the DC offset
  • switching the MEMS antenna switch to the correct band
  • starting the transmit of the actual burst data

To synchronize those events, and to schedule them in sequence before the burst is transmitted, the TSP is used.

Parallel vs. Serial

In early GSM transceivers, all the events could be driven by dedicated electrical lines from the TPU.

However, in multi-band configurations and with integrated baseband codec circuits, it made more sense to
have a serial interface to limit the number of signals that need to be routed between components.

TSP Signals

In the Calypso/Iota/Rita based modem designs, the TSP is only used uni-directional, i.e. from the DBB to the peripherals.
Thus, only the following signals are needed:
  • TEN (TSP Enable), one for each peripheral
  • CLK13M - the 13MHz clocl that runs everywhere
  • TDX (TSP Data Tx) (used bi-directional for RF6151C)