An asynchronous FIFO is used to pass data from a 100 MHz write clock domain to a 50 MHz read clock domain. The producer writes a continuous burst of 80 items at a rate of 1 item per write clock cycle. The consumer reads at a rate of 1 item per read clock cycle. What is the absolute minimum FIFO depth required to guarantee no data is dropped during this burst?
The write clock period is 10 ns, and the read clock period is 20 ns. Writing 80 items takes 80 x 10 ns = 800 ns. During this 800 ns burst, the consumer is simultaneously reading. The number of items read in 800 ns is 800 ns / 20 ns = 40 items. The maximum number of items buffered in the FIFO at the end of the burst is the total written minus the total read: 80 - 40 = 40 items.
