Constant IRQ_RX_BATCH_CAPACITY 

pub const IRQ_RX_BATCH_CAPACITY: usize = 64; // 64usize

Maximum number of normalized RX samples returned by one hard-IRQ pass.

A full batch leaves the device source pending or reasserted so a later IRQ can continue draining. Keeping the capacity in the portable value type makes the hard-IRQ work and stack footprint independent of runtime policy.