DDR memory controller
A DDR memory controller is described wherein a core domain capture clock is created by programmably delaying the core clock of the memory controller. The delay of this capture clock is calibrated during a power on the initialization sequence in concert with a DDR memory in a system environment, thereby minimizing the effects of system delays and increasing both device and system yield. An additional embodiment also includes programmably delaying the incoming dqs signal.
1. A DDR memory controller for read operations, comprising:
a dqs clock driven by a DDR memory;
a core clock originating within the DDR memory controller;
a dqs delay element producing a delayed dqs;
a dq read data register clocked by the delayed dqs;
a core clock delay element that produces a capture clock;
a first core domain register responsive to said dq read data register and clocked by said capture clock;
a second core domain register responsive to said first core domain register and clocked by the core clock;
a self-configuring logic circuit responsive to said read data register and said first and second core domain registers, for controlling said core clock delay element; and
wherein the delay of the core clock delay element is set by said self-configuring logic circuit during a power-on initialization test and calibration operation.
2. The DDR memory controller of claim 1 wherein the method for operating the self-configuring logic circuit during power-on initialization comprises the steps of:
storing a pre-determined test data pattern in the DDR memory;
specifying a minimum expected passing window size;
for each increment of CAS latency, for each increment of delay tap setting for the core clock delay element, and for each byte lane, running a read data capture test using the stored test data pattern and recording the results as pass or fail;
from the recorded results, choosing the delay tap setting that positions the capture clock in the center of the largest passing window; and
programming the chosen delay tap setting into control registers in the DDR memory controller.
3. The DDR memory controller of claim 1 wherein the dqs delay element is a programmable delay element whose delay value is set by a self-configuring logic circuit responsive to said read data register and said first and second core domain registers and wherein the delay of the dqs delay element is set by said self-configuring logic circuit during a power-on initialization test and calibration operation.
4. The DDR memory controller of claim 1 further including a CAS latency compensation circuit that is clocked solely by the core clock.
5. A DDR memory controller for read operations, comprising:
a dqs clock driven by a DDR memory;
a core clock originating within the DDR memory controller;
a dqs delay element producing a delayed dqs;
a dq read data register clocked by the delayed dqs;
a core clock delay element that produces a capture clock;
a first core domain register responsive to said dq read data register and clocked by said capture clock;
a second core domain register responsive to said first core domain register and clocked by the core clock;
a self-configuring logic circuit responsive to said read data register and said first and second core domain registers, for controlling said core clock delay element and said dqs delay element; and
wherein the delay tap setting of the core clock delay element and the delay tap setting of the dqs delay element are set by said self-configuring logic circuit during power-on initialization.
6. The DDR memory controller of claim 5 wherein the method for operating the self-configuring logic circuit during power-on initialization comprises the steps of:
storing a pre-determined test data pattern in the DDR memory;
specifying a minimum expected passing window size;
for each increment of CAS latency, for each increment of delay tap setting for the core clock delay element, for each increment of delay tap setting for the dqs delay element, and for each byte lane, running a read data capture test using the stored test data pattern and recording the results as pass or fail;
from the recorded results, choosing the delay tap settings for the core clock delay element and the dqs delay element that positions the capture clock in the center of the largest passing window; and
programming the chosen delay tap settings into control registers in the DDR memory controller.
7. The DDR memory controller of claim 5 further including a CAS latency compensation circuit that is clocked solely by the core clock.
8. A method for capturing read data in a DDR memory controller comprising the steps of:
capturing the dq read data supplied by a DDR memory in a read data register that is clocked by a delayed version of dqs;
capturing the output of the read data register in a first core domain register that is clocked by a delayed version of core clock supplied by a core clock delay element;
capturing the output of said first core domain register in a second core domain register that is clocked by core clock; and
wherein the delay tap setting for the core clock delay element is determined during a power-on initialization test and calibration operation such that said delayed version of core clock is positioned in the center of the largest passing window.
9. The method of claim 8 for capturing read data in a DDR memory controller further comprising the step of:
delaying the signal output from the second core domain register by a programmable number of cycles of the core clock in order to compensate for CAS latency characteristics of a particular system installation, said programmable number of cycles being determined during a power-on initialization test and calibration operation.