Day 74: Peripheral: the 32-bit timer
Peripheral: the 32-bit timer
A timer/counter gives software a sense of time. At its core: a 32-bit counter that increments each clock (or each prescaled tick), a compare/reload value, and an interrupt when the counter reaches it. From this you get periodic interrupts (RTOS tick), one-shot delays, and — with an output toggle — PWM. It's your Stage-0 counter plus compare logic plus a register interface.
always @(posedge clk or negedge rst_n) begin
if (!rst_n) begin count <= 0; irq <= 0; end
else if (enable) begin
if (count == 0) begin
count <= reload; // auto-reload for periodic mode
irq <= 1'b1; // fire interrupt
end else begin
count <= count - 1'b1;
if (irq_clear) irq <= 1'b0;
end
end
end
// a prescaler (divide clk by N) sets the tick period; reload sets the countThis drives your RTOS tick later
The periodic interrupt from this timer is exactly what a scheduler needs for time-slicing — you'll use it in Stage D's FreeRTOS work, and in Stage 4 firmware for delays. A prescaler (divide the clock before counting) lets one 32-bit timer span microseconds to minutes. Small module, huge reuse.
Ship for Day 74
What is the purpose of a timer’s prescaler?
