Efficient RAM usage in computing devices
Systems and methods are disclosed for managing program code in a computing device, such as an embedded system. In a computing device, a non-volatile flash memory stores program code comprising initialization code designed to be executed a single time during device booting, main program code separate from the initialization code, and main code loader code designed to direct a controller of the computing device to load the main program code from the flash memory to the RAM when executed by the controller. The controller loads the initialization code and the main code loader code to first and second adjacent portions of the RAM, respectively, and loads the main program code, separately from the initialization code, to a third portion of the RAM at least partially overlapping the first portion but not overlapping the second portion, thereby at least partially overwriting the initialization code.
1. A computing device comprising:
a volatile random access memory (RAM);
a non-volatile flash memory storing program code comprising:
initialization code designed to be executed a single time during device booting;
main program code separate from the initialization code and designed to be executed after execution of the initialization code; and
main code loader code designed to direct the controller to load the main program code from the flash memory to the RAM when executed by the controller; and
a controller configured to:
load the initialization code and the main code loader code to first and second adjacent portions of the RAM, respectively;
load the main program code, separately from the initialization code, to a third portion of the RAM at least partially overlapping the first portion but not overlapping the second portion, thereby at least partially overwriting the initialization code; and
execute the main program code.
2. The computing device of claim 1 , wherein: the initialization code comprises X bytes of data; the main program code comprises Y bytes of data; the RAM consists of less than Z bytes of storage space; and Z=X+Y.
3. The computing device of claim 1 , wherein the controller is further configured to:
load the initialization code and the main code loader code as part of a first load operation; and
load the main program code as part of a second load operation executed subsequently to the first load operation.
4. The computing device of claim 1 , wherein the controller is further configured to execute the main program code without using program overlays.
5. The computing device of claim 1 , wherein the initialization code and main program code are separately-compiled pieces of code.
6. The computing device of claim 1 , wherein the initialization code comprises code that, when executed, directs the controller to perform power-on self-testing and initialize one or more peripheral devices.
7. A computing device comprising:
a volatile random access memory (RAM);
a non-volatile flash memory storing program code comprising:
initialization code designed to be executed a single time during device booting;
initialization code loader code designed to direct the controller to load the initialization code from the flash memory to the RAM when executed by the controller;
main program code separate from the initialization code and designed to be executed after execution of the initialization code; and
main code loader code designed to direct the controller to load the main program code from the flash memory to the RAM when executed by the controller; and
a controller configured to:
load the initialization code loader code to a first portion of the RAM;
in response to execution of the initialization code loader code from the RAM, load the initialization code to a second portion of the RAM;
load the main code loader code to a third portion of the RAM that overlaps at least one of the first portion and the second portion; and
in response to execution of the main code loader code, load the main program code to a fourth portion of the RAM at least partially overlapping the second portion but not overlapping the third portion, thereby at least partially overwriting the initialization code.
8. The computing device of claim 7 , wherein: the initialization code comprises X bytes of data; the main program code comprises Y bytes of data; and the RAM consists of less than Z bytes of storage space; and Z=X+Y.
9. The computing device of claim 7 , wherein the initialization code comprises code that, when executed, directs the controller to perform power-on self-testing and initialize one or more peripheral devices.
10. The computing device of claim 7 , wherein the flash memory, RAM and controller are components of an embedded system.
11. The computing device of claim 7 , wherein the controller is further configured to:
load the initialization code and the main code loader code as part of a first load operation; and
load the main program code as part of a second load operation executed subsequently to the first load operation.
12. The computing device of claim 7 , wherein the third portion and fourth portion are disposed adjacent to one another in the RAM.
13. The computing device of claim 7 , wherein the controller is further configured to execute the main program code without using program overlays.
14. The computing device of claim 7 , wherein the controller is further configured to execute the initialization code without saving global data for use by the main program code.
15. The computing device of claim 7 , wherein the initialization code and main program code are separately-compiled pieces of code.
16. A method of booting a computing device, the method comprising:
loading initialization code loader code from a non-volatile flash memory to a first portion of a volatile random access memory (RAM), the initialization code loader code being designed to cause initialization code to be loaded from the flash memory to the RAM when executed;
executing the initialization code loader code;
in response to said executing the initialization code loader code from the RAM, loading the initialization code to a second portion of the RAM;
executing the initialization code;
in response to said executing the initialization code, loading main code loader code to a third portion of the RAM that overlaps at least one of the first portion and the second portion, the main code loader code being designed to cause main program code to be loaded from the flash memory to the RAM when executed;
executing the main code loader code;
in response to said executing the main code loader code, loading the main program code to a fourth portion of the RAM at least partially overlapping the second portion but not overlapping the third portion, thereby at least partially overwriting the initialization code; and
executing the main program code.
17. The method of claim 16 , wherein: the initialization code comprises X bytes of data; the main program code comprises Y bytes of data; the RAM consists of less than Z bytes of storage space; and Z=X+Y.
18. The method of claim 16 , wherein the third portion and fourth portion are disposed adjacent to one another in the RAM.
19. The method of claim 16 , wherein the main program code comprises at least one of operating system code and hardware device driver code.
20. The method of claim 16 , wherein the initialization code and main program code are separately-compiled pieces of code.