Dynamic frequency memory control
A memory controller ( 40 ) is adaptable to scaling of a system clock frequency, to enable another device ( 10 ) to access a memory ( 20 ), and has a part for outputting control signals having some timing characteristics not entirely scalable with scaling of the system clock frequency. In response to an indication of a change in a frequency of the system clock, the memory controller adapts the part autonomously to enable it to output new digital memory control signals synchronized to the changed system clock and which also have the non scalable timing characteristics. This avoids the need for the processor to adapt the memory controller. Hence the adaptation can be carried out more quickly, leading to less disruption to other parts of the system and means the frequency scaling can be carried out more often.
1. A method of producing digital memory control signals to enable other devices to access a memory in synchronization with a system clock, the method comprising using a memory controller in communication with the memory to perform autonomously the steps of:
receiving a memory access request from the one of the other devices;
outputting digital memory control signals synchronized to the system clock to the memory in response to the memory access request, the digital memory control signals comprising non scalable timing characteristics comprising terms independent of a system clock frequency that are not scalable with scaling of the system clock frequency and scalable timing characteristics that depend on the system clock frequency;
monitoring a system clock frequency; and
determining and outputting new digital memory control signals that are different from the memory control signals output prior to the change of the clock frequency in response to a change of the system clock frequency, the new digital memory control signals including the scalable timing characteristics which are scaled according to the change in the system clock frequency, and the non scalable timing characteristics which are the same as in the digital memory control signals prior to the change of the clock frequency.
2. A non-transitory machine readable storage medium storing a computer program that when executed by a computer causes the computer to perform a method of producing digital memory control signals to enable other devices to access a memory in synchronization with a system clock, the method comprising using a memory controller in communication with the memory to perform autonomously the steps of:
receiving a memory access request from the one of the other devices;
outputting digital memory control signals synchronized to the system clock to the memory in response to the memory access request, the digital memory control signals comprising non scalable timing characteristics comprising terms independent of a system clock frequency that are not scalable with scaling of the system clock frequency and scalable timing characteristics that depend on the system clock frequency;
monitoring a system clock frequency; and
determining and outputting new digital memory control signals that are different from the memory control signals output prior to the change of the clock frequency in response to a change of the system clock frequency, the new digital memory control signals including the scalable timing characteristics which are scaled according to the change in the system clock frequency, and the non scalable timing characteristics which are the same as in the digital memory control signals prior to the change of the clock frequency.
3. A memory controller configured to produce digital memory control signals to enable other devices to access a memory in synchronization with a system clock, the memory controller comprising:
an interface configured to receive a memory access request from one of the other devices; and
a signal generation part configured to output the digital memory control signals synchronized to the system clock in response to the memory access request, the control signals comprising non scalable timing characteristics comprising terms independent of a system clock frequency that are not scalable with scaling of the system clock frequency, and scalable timing characteristics that depend on the system clock frequency;
wherein, in response to a change of the system clock frequency, the signal generation part autonomously outputs new digital memory control signals different from the memory control signals output prior to the change of the clock frequency, the new digital memory control signals including the scalable timing characteristics which are scaled according to the change in the system clock frequency and the non scalable timing characteristics which are the same as in the digital memory control signals prior to the change of the clock frequency.
4. The memory controller of claim 3 , wherein the memory controller further comprises a storing device configured to store a representation of the non scalable timing characteristics in order to adapt the signal generation part.
5. The memory controller of claim 4 , wherein the memory controller is further configured to convert the retrieved representation into timing characteristics in terms related to the change in the system clock frequency, for use in generating the new digital memory control signals.
6. The memory controller of claim 3 , wherein the memory controller is further configured to select from a number of predetermined stored signal sequences, each corresponding to a different system clock frequency, in order to adapt the signal generation part.
7. The memory controller of claim 3 further comprising a frequency change detector in communication with the system clock and configured to detect the change in the system clock frequency and to output an indication of the change.
8. The memory controller of claim 3 , wherein the memory controller is in communication with an external device and is configured to receive an indication of the change in system clock frequency from the external device.
9. The memory controller of claim 3 , wherein the interface comprises a bus interface, other devices being coupled to the bus interface, and the memory controller is configured to block any of the other devices coupled to the bus interface from initiating a memory access while the memory controller is adapting the signal generation part.
10. The memory controller of claim 3 , wherein the memory control signals are suitable for a dynamic memory device having a refresh cycle.
11. A system comprising the memory controller of claim 3 , a processor and the memory.
12. The system of claim 11 , wherein the processor is configured to determine a level of processing demand, and to scale the system clock frequency according to the level of processing demand.
13. The memory controller of claim 3 , wherein the memory controller further comprises internal registers, the internal registers comprising memory controller timing parameters and a current value for the system clock frequency, wherein the memory controller in adapting the signal generation part autonomously changes the memory controller timing parameters stored in the internal registers.
14. The memory controller of claim 3 , wherein the signal generation part comprises an internal state machine comprising clock values for generating the digital memory control signals, wherein the memory controller in adapting the signal generation part autonomously changes the internal state machine.
15. A personal mobile device having the system of claim 11 .