AVR Core

lbuild module: modm:platform:core

Implements the interfaces defined in the :architecture modules. Adds the -mmcu={target} compile flag and the F_CPU={core frequency} define.

Blocking Delay

The delay functions as defined by modm:architecture:delay and called with a constant value are implemented directly via GCC's __builtin_avr_delay_cycles(ns / (1e9 / F_CPU)). Constant delays are therefore fairly accurate.

For delays with a dynamic time, the following limitations apply for nanoseconds:

• The input is limited to 16-bit nanoseconds, so ~65 microseconds.
• The minimum delay is between 5-10 cycles, so even at the fastest clock rate of 32MHz a delay below ~250ns is not possible. At 8MHz delays less than 1us are not possible.
• For longer delays, the 3-cycle _delay_loop_1(loops) is used and the number of loops should be calculated by dividing the input value by ns_per_loop = 3e9/F_CPU. However, division is prohibitively slow and thus very coarsly approximated by shifting the input: ns >> ceil(log_2(ns_per_loop)). This is only accurate for 3e9/2^7 = 23.4MHz, 11.7MHz, 5.8MHz, etc. For all other clock speeds the error is bound by a factor of 2, so the delay is at most twice as long as expected.

For micro- and milliseconds delays with dynamic time:

• Microseconds delay is implemented fairly accurately in 1us steps with a maximum time delay of 65ms for clocks larger than 6MHz, or .
• Millisecond delay is implemented fairly accurately in 1ms steps on 32-bits of input time.

This module is only available for avr.

Options

f_cpu

CPU clock frequency

Default: None
Inputs: [1 ... 32000000]

Dependencies

Limited availability: Check with 'lbuild discover' if this module is available for your target!