AN: Capstone Dive Computer Example - Quantum Leaps

Application Note:
Capstone Dive Computer Example
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(12) The transmit pin GPIO3.4 is configured as output, alternative function 3 (UART0 Tx) using the
ST driver library interface.
(13) The UART0 is not properly configured using the ST driver library interface.
(14) The QS filters are setup (see Chapter 11 in [PSiCC2] as well as “QP Reference Manual”
online).
(15) The QS_onStartup() callback returns 1, meaning that the QS initialization was successful.
(16) The QS_onCleanup() callback is empty for MSP430 (the application never exits).
(17-21) The QS_onGetTime() callback provides a fine-granularity timestamp. The timestamp is discussed
in the next section.
(22) The QS_onFlush() callback flushes the QS trace buffer to the host. Typically, the function busywaits
for the transfer to complete. It is only used in the initialization phase for sending the QS
dictionary records to the host.
(23) The implementation of QS for STR912 uses the block-oriented QS-buffer interface
QS_getBlock(), which provides up to 16 bytes to fill the FIFO of the UART (see Chapter 11 in
[PSiCC2]).
(24) The QS_onFlush() callback busy-waits in-line until the transmit buffer is empty.
(25) The data byte is inserted into the UART0 data register.
3.1 QS Time Stamp Callback QS_onGetTime()
The platform-specific QS port must provide function QS_onGetTime() (Listing 5(17-21)) that returns
the current time stamp in 32-bit resolution. To provide such a fine-granularity time stamp, the BSP
uses the free running Timer 3, which is the same timer already used for generation of the system
clock-tick interrupt.
NOTE: The QS_onGetTime() callback is always called with interrupts locked.
Figure 7 shows how the Timer 3 Count Register (TIM3->CNTR) reading is extended to 32 bits.
The drawing below shows a free running Timer 3 Count Register (TIM3->CNTR) that counts up from
0 to 0xFFFF and rolls over to 0. If the system tick rate is faster than the rollover rate then you
could ‘oversample’ this free-running timer by reading it in the clock tick ISR.
The 32-bit variable l_currTime32 contains the sum of the 16-bit deltas from each readout of the
free running Timer 3 Count Register. Because of unsigned 16-bit arithmetic used in Listing 5(19),
even a ‘small’ current value minus a ‘large’ previous value still results in the proper delta. Note that
QS_onGetTime() can actually be called at just about any time and thus, also needs to update
l_currTime32 before it returns the current value.
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