arduino timer interrupt causes code to fail with gps

There is a burst function which allows the clock to be validated when an external signal is high. This allows counting on the opposite edges of the clock. The selected clock can be inverted using the CLKI bit in TC_CMR. External clock signals: XC0, XC1 or XC2.Internal clock signals: TIMER_CLOCK1, TIMER_CLOCK2, TIMER_CLOCK3, TIMER_CLOCK4, TIMER_CLOCK5.In this case, the counter value resets to 0x00000000 on the next valid edge of the selected clock following the trigger event.Īt the block level, input clock signals of each channel can either be connected to the external inputs TCLK0, TCLK1 or TCLK2, or be connected to the internal I/O signals TIOA0, TIOA1 or TIOA2 for chaining by programming the TC_BMR (Block Mode) register.Įach channel can independently select an internal or external clock source for its counter via the TCCLKS bits in the TC Channel Mode register (TC_CMR).

The counter can also be reset by a trigger. The current value of the counter is accessible anytime by reading the Counter Value Register, TC_CV. When the counter has reached the value 0xFFFFFFFF and wraps around to 0x00000000, an overflow occurs and the COVFS bit in TC_SR (Status Register) is set. The value of the counter is incremented at each positive edge of the selected clock. The three channels of TC are identical in operation except when Quadrature decoder is enabled.Įach channel is organized around a separate 32-bit counter.

TIOB - Capture Mode: TC Input, Waveform Mode: TC I/O.

TIOA - Capture Mode: TC Input, Waveform Mode: TC Output.

It is not as bad as it looks.Ĭhannel signals seen above are as follows: This rather daunting image is the Timer Counter block diagramme. I may get into clock chaining in further detail in a separate post. As will be seen later, TCs can be chained together using the TIOA0, TIOA1, TIOA2 as an external clock input for subsequent TCs allowing further division of the clock frequency. It should be noted that it is possible to select the slow clock as the master clock, which case TIMER_CLOCK5 input is equivalent to the master clock. MCK is the master clock (84 MHz) and SLCK is the slow clock (32 kHz). The Block Mode Register defines the external clock inputs for each channel, allowing them to be chained.Ĭlocks are assigned to Timer Counters as follows: The Block Control Register allows the three channels to be started simultaneously with the same instruction. The TC block has two global registers which act upon all three TC channels. We will not be covering this feature in these postings. When enabled, the quadrature decoder performs input line filtering and decoding of quadrature signals. The TC embeds quadrature decoder logic connected in front of the 3 timers and driven by TIOA0, TIOB0 and TIOA1 inputs. Each channel drives an internal interrupt signal which can be programmed to generate processor interrupts. Each channel can be independently programmed to perform a wide range of functions including frequency measurement, event counting, interval measurement, pulse generation, delay timing and pulse width modulation (PWM).Įach channel has three external clock inputs, five internal clock inputs and two multi-purpose input/output signals which can be configured by the user. Each TC includes three identical 32-bit channels. The SAM3X8E CPU has 3 Timer Counters (TCs) named TC0, TC1, TC2. There is a lot of functionality in the Due Timer Counter module and it is not a simple thing to describe it fully so I will likely break this into several postings. The Arduino Due Timers or Counter Timer (TC) as they are called are a bit different implementation from the 8 bit Arduino devices.

I will endeavour to keep things as simple and practical as I can. Tighten up the seat belt as this world gets deep in a hurry. My next foray into the wild and wonderful world of Arduino Due will be to take a close look at the Due notion of Timers.

Arduino timer interrupt causes code to fail with gps