Maintaining dynamic count of fifo contents in multiple clock domains

A method of generating a read count value in a write clock domain from read strobes generated in a read clock domain indicating a number of open slots present in a FIFO comprising:

• writing said read strobes to sequential storage devices in a parallel register in response to a read clock signal and simultaneously clearing other devices in said parallel register;
• transferring data stored in said sequential storage devices to synchronizers in response to said read clock signal;
• detecting a leading edge of said data transferred from said sequential storage devices;
• generating a decrement pulse in said synchronizers in said write clock domain;
• applying said decrement pulses to an up/down counter in parallel to decrement said up/down counter;
• incrementing said up/down counter upon receipt of a write strobe pulse;
• generating a read counter value in said read clock domain that is indicative of said number of open slots that are present in said FIFO.

A device for generating a write counter value in a read clock domain to indicate the amount of data that is present in a FIFO comprising:

• steering/reset logic that generates a write output pulse in said write clock domain on sequential outputs and simultaneously generates a reset pulse on other outputs;
• a parallel register that stores said write output pulse and generates a edge signal in said write clock domain;
• synchronizers connected in parallel to said parallel register that detect said rising edge signal and generate increment pulses in said read clock domain;
• an up/down counter that receives said increment pulses in parallel and increments said up/down counter in response to said increment pulses, and receives a read strobe pulse and decrements said up/down counter in response to said read strobe pulse, said up/down counter having a counter output that provides a write count signal;
• a register that generates a write counter value in said read clock domain that indicates the amount of data that is present in said FIFO.

A device for generating a read counter value in a write clock domain from read strobes generated in a read clock domain to indicate the number of slots open in a FIFO comprising:

• steering/reset logic that generates a read output pulse in said read clock domain on sequential outputs and simultaneously generates a reset pulse on other outputs;
• a parallel register that stores said read output pulse and generates a rising edge signal in said read clock domain;
• synchronizers connected in parallel to said parallel register that detect said rising edge signal and generate decrement pulses in said write clock domain;
• an up/down counter that receives said decrement pulses in parallel and decrements said up/down counter in response to said decrement pulses, and receives a read strobe pulse and increments said up/down counter in response to said write strobe pulse, said up/down counter having a counter output that provides a read count signal;
• a register that generates a read counter value in said write clock domain that indicates the amount of data that is present in said FIFO.