Peripheral interface circuit for serial memory
View Patent ↗A peripheral interface circuit and method is disclosed for dealing with round trip delay with serial memory. In some implementations, a finite state machine is configured to introduce a delay state prior to a read data state to absorb round trip delay associated with a memory read operation. A clock module is coupled to the finite state machine and configured to delay start of a pad return clock for the read operation until completion of the delay state. A first synchronous logic is coupled to receive the pad return clock and is configured to sample and hold data from a data bus during the read data state of the memory read operation based on the pad return clock. A second synchronous logic is coupled to receive a system clock and is configured to sample the held data based on the system clock.
1. A peripheral interface circuit for serial memory, the circuit comprising:
a sampling queue configured to sample a data line during a read data state of a memory read operation and write the sampled data into an element of the sampling queue pointed to by a write pointer;
a finite state machine configured to introduce a delay state after a dummy cycle state and prior to the read data state to absorb round trip delay associated with the memory read operation;
write pointer logic coupled to the sampling queue and configured to generate the write pointer, the write pointer logic configured to be responsive to the delay state introduced prior to the read data state;
resynchronization logic coupled to the write pointer logic and configured to resynchronize the write pointer;
sampling logic coupled to the sampling queue, the sampling logic configured to sample the element of the sampling queue, which is pointed to by a read pointer;
read pointer logic coupled to the sampling logic and configured to generate the read pointer; and
pointer comparison logic coupled to the read pointer logic and the resynchronization logic, the pointer comparison logic configured to trigger the sampling logic to sample the element of the sampling queue pointed to by the read pointer.
2. The peripheral interface circuit of claim 1 , where the peripheral interface circuit is a quad serial peripheral interface (QSPI).
3. The peripheral interface circuit of claim 1 , where the sampling queue and write pointer logic are coupled to a pad return clock and the resynchronization logic, read pointer logic and sampling logic are coupled to a system clock, and the pad return clock and system clock have different clock frequencies.
4. The peripheral interface circuit of claim 1 , where the read pointer logic is configured to increment the read pointer based on output of the pointer comparison logic.
5. The peripheral interface circuit of claim 1 , where the sampling queue includes N elements comprising N delay flip-flops.
6. The peripheral interface circuit of claim 1 , where the resynchronization logic includes two or more delay flip-flops coupled in series.
7. A method of dealing with round trip delay with serial memory, the method comprising:
sampling, by a sample queue, a data line during a read data state of a memory read operation and writing the sampled data into an element of a sampling queue pointed to by a write pointer;
generating, by a finite state machine, a delay state following a dummy cycle state and prior to the read data state to absorb round trip delay associated with the memory read operation;
generating, by write pointer logic, the write pointer, the write pointer logic configured to respond to the delay state introduced prior to the read data state;
resynchronizing, by the write pointer logic, the write pointer;
sampling, by sampling logic, the element of the sampling queue, which is pointed to by a read pointer;
generating, by read pointer logic, the read pointer; and
triggering, by pointer comparison logic, the sampling logic to sample the element of the sampling queue pointed to by the read pointer.