Clocking Scheme; Bluetooth And Fm Rds Radio Module - Nokia N900 Service Manual

RX-51
System Module

Clocking scheme

RX-51 has two different clocking schemes. Both APE and CMT side have their own clocking system.
Two main clocks are provided for the APE system: 19.2 MHz clock produced by a crystal oscillator for Gaia and
OMAP3, and 32.768 kHz sleep clock produced by Gaia with an external crystal for sleeping functionality. OMAP3
has internal PLLs which then create clock signals for other peripheral devices/interfaces like USB and RS MMC,
LCD and memories.
WLAN and BT have independent BTSYSCLK which is generated by VCTCXO. They can request btsysclk
independently, which enables sleeping/wakening even though OMAP is sleeping or woken up.
32k Sleep Clock is always powered on after start-up. Sleep clock is used for low-power operation.
There are two main clocks in the CellMo system: 38.4 MHz RF clock produced by VCTCXO in RF section and
32.768 kHz sleep clock produced by the EM ASIC Gazoo with an external crystal. RF clock is generated only
when VCTCXO is powered on by the EM ASIC regulator. The regulator itself is activated by SleepX signal from
RAPUYAMA. When both CPUs of RAPUYAMA are in sleep, RF clock is stopped. RAPUYAMA has internal PLL that
creates clock signals for other peripheral devices/interfaces, such as SIM, I2C and memories.
Figure 51 Clocking scheme

Bluetooth and FM RDS radio module

Bluetooth and FM radio receiver are provided by the same ASIC (Broadcom BCM2048). The device supports
Bluetooth operation and FM radio rececption in both European and USA bands. The UART interface allows the
device to communicate with the phone baseband engine using Bluetooth HCI commands. Commands to the
FM radio can also be sent over the I2C interface.
When Bluetooth is switched on, the phone user interface the BT_RESETX line is toggled to reset the Bluetooth
device, and commands are sent over the UART interface to configure the device. If UART communication fails
(due to a hardware fault) it will not be possible to switch on Bluetooth from the phone user interface.
The device has two clock signals: BTSYSCLK (19.2MHz, 26.0MHz, or 38.4MHz supported) and SLEEP_CLK
(32.768kHz). The SLEEP_CLK is supplied all the time the phone is switched on. To maximise the phone standby
time, it is only necessary to provide a BTSYSCLK signal when Bluetooth activity occurs, such as sending
Bluetooth data to another device, or checking periodically if there are any other Bluetooth devices attempting
to communicate with it. At other times when the Bluetooth device is in standby mode or the FM radio is
switched on it is only necessary to provide a SLEEP_CLK signal. The Bluetooth-FM ASIC is powered directly from
the phone battery voltage line (VBAT). An internal regulator is enabled when Bluetooth or FM radio is switched
on.
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