Variable read latency on a serial memory bus
View Patent ↗Systems and/or methods are provided that facilitate employing a variable read latency on a serial memory bus. In an aspect, a memory can utilize an undefined amount of time to obtain data from a memory array and prepare the data for transfer on the serial memory bus. The serial memory bus can be driven to a defined state. When data is ready for transfer, the memory can assert a start bit on the serial memory bus to notify a host prior to initiating the data transfer.
1. A method, comprising:
receiving, over a data bus, a read request from a host device;
implementing a variable latency period during a read operation including driving the data bus to a defined state after passage of a predetermined time period, wherein a memory array is accessed for target data responsive to the read request during the read operation;
asserting a start indication on the data bus, wherein the start indication is opposite to the defined state; and
transferring the target data to the host device a defined number of clock cycles after asserting the start indication.
2. The method of claim 1 , wherein the implementing comprises driving the data bus to a low state and the asserting comprises driving the data bus to a high state.
3. The method of claim 1 , wherein the implementing comprises driving the data bus to a high state and the asserting comprises driving the data bus to a low state.
4. The method of claim 1 , wherein the data bus comprises a Serial Peripheral Interface bus.
5. The method of claim 1 , wherein the asserting the start indication on the data bus comprises asserting a start bit on the data bus, wherein the start bit is a one bit.
6. The method of claim 1 , wherein the asserting the start indication on the data bus comprises asserting a start bit on the data bus, wherein the start bit is a zero bit.
7. The method of claim 1 , wherein the predetermined time period comprises at least one clock cycle, wherein the at least one clock cycle comprises a handover time.
8. The method of claim 7 , wherein the data bus is driven to the defined state by the host device and a memory device during the handover time.
9. The method of claim 1 , further comprising accessing the memory array to obtain the target data during the variable latency period, wherein the target data is associated with an address.
10. The method of claim 1 , wherein the asserting the start indication on the data bus comprises determining the target data from the memory array is ready and asserting a start bit on the data bus.
11. The method of claim 10 , wherein the start bit is a first bit of a read preamble and comprises a known data pattern.
12. The method of claim 11 , further comprising determining a capture time based upon the read preamble.
13. A memory device, comprising:
a serial peripheral interface that enables the memory device to interact with another device according to a Serial Peripheral Interface protocol;
a memory array that retains information, wherein access to the memory array to obtain information associated with an address requires an undefined amount of time, wherein the serial peripheral interface accesses the memory device to read data in response to a read request from the another device, and wherein the serial peripheral interface drives a data bus of the interface to a defined state after passage of a predetermined time period while the data is being read from the memory device; and
a latency module that asserts a start bit on the interface when the data read from the memory device is ready to be conveyed to the another device, wherein the start bit is an opposite state to the defined state.
14. The memory device of claim 13 , wherein the defined state is a low state and the start bit is a one bit.
15. The memory device of claim 13 , wherein the defined state is a high state and the start bit is a zero bit.
16. The memory device of claim 13 , wherein the predetermined time period comprises at least one clock cycle, wherein the at least one clock cycle comprises a handover time.
17. A device, comprising:
a controller that communicates a read request to a memory device via a Serial Peripheral Interface bus, wherein a serial peripheral interface drives a data bus of the Serial Peripheral Interface bus to a defined state after passage of a predetermined time period while data is being read from the memory device; and
a detection module that observes transition of the data bus from the defined state, wherein the transition indicates that the memory device is ready to respond to the read request.
18. The device of claim 17 , wherein the controller issues a command and an address to the memory device via the data bus and drives the data bus to the defined state for the predetermined time period.
19. The device of claim 17 , wherein the predetermined time period comprises a handover time during which the controller and the serial peripheral interface drive the data bus to the defined state.
20. The device of claim 17 , wherein the predetermined time period comprises at least one clock cycle, wherein the at least one clock cycle comprises a handover time.