Interrupt Generation - Motorola DragonBall MC9328MX1 Reference Manual

Bluetooth Accelerator (BTA)
Table 16-2. Bluetooth Clocks and Counters (Continued)
Name Bit Size
EstimatedClk 28
OffsetClk 28
When the unit is the master of a piconet, its NativeClk is used for timing of slots, hopping frequency
sequence, whitening/de-whitening initialization, and so on.
NativeClk is a free-running 28 bit counter updated at a frequency of 3.2 kHz. The 3.2 kHz clock is
generated by dividing the high precision 8 MHz clock by 2,500 using a 12-bit counter (NativeCount).
Bluetooth specifications stipulate that, in connection states of high activity, a worst case accuracy of ± 20
ppm is expected for the native clock. In low-power states (Standby, Hold or Park modes), a relaxed
accuracy of ± 250 ppm is allowed.
When temperature drift and aging are taken into account, the requirement
of the high precision clock is more likely to be around ± 10 ppm.
EstimatedClk is a clock that is maintained by the unit when it operates as a slave, and it keeps track of a
remote master's NativeClk. During a page scan, when the slave unit receives an access code trigger from
the master, it presets the EstimatedCount with an expected count and sets the two least significant bits of
EstimatedClk to "00." This value causes the unit to respond 625 µs later, relative to the beginning of the
time slot, regardless of whether it receives the first or second page within the time slot.
Later in the link setup, the EstimatedClk is updated with the remote master's native clock, which is sent in
the FHS packet. EstimatedClk is incremented by the EstimatedCount. During active connection state,
whenever the access code is triggered from the master's transmission, EstimatedCount is updated with an
expected count, therefore preventing the EstimatedClk from drifting away from the remote master's
NativeClk.
A third value, OffsetClk, maintains the difference between EstimatedClk and NativeClk. OffsetClk is
updated at every NativeClk tick. Writing to the OFFSET_CLK_LOW and OFFSET_CLK_HIGH registers
will update EstimatedClk with the sum of NativeClk and OffsetClk on the next NativeClk tick.

16.3.1.2.2 Interrupt Generation

The Bluetooth core provides three interrupt lines:
1. A combination of three interrupts that are Logical-OR'ed together into a single active-high
wire. This one-shot interrupt is termed "BTsys."
2. An interrupt triggered by the Bluetooth application timer termed "BTtim."
3. An interrupt generated during the wake-up sequence termed "BTwui."
The interrupts are summarized and described in Table 16-3 on page 16-7.
16-6
Input Frequency Precision
3.2 kHz Low (power down)
High (operation)
3.2 kHz Low (power down)
High (operation)
NOTE:
MC9328MX1 Reference Manual
Purpose
Estimate of the remote master's
NativeClk. Set by software and updated
by the EstimatedCount.
Difference between NativeClk and
EstimatedClk. This is updated each
SysTick.
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