Improving The Real-Time Ability Of Bill Acceptor System Based On ARM And UClinux

With the development of the self-service business in China, the bill acceptor system based on SCM (Single Chip Micyoco) as the key part of vending machine is restricted on the functionality and capability.In this thesis, the research about the bill acceptor which is not based on SCM but uClinux (a special port of the Linux) and S3C4510B (ARM microcontroller) has been done. The bill acceptor has the requirement on hard real-time ability, but uClinux can not meet the requirement. uClinux is powerful and efficient, and it also has a lot of free resource that can be used for development. If the real-time ability of the bill acceptor can be met, the bill acceptor can be more predominant on cost, functionality and capability, so improving the real-time ability is very important for the development of the bill acceptor.In this bill acceptor system, the bill characteristic data acquisition subsystem needs the support of hard real-time ability, so whether can meet this requirement of hard real-time ability is the key of the bill acceptor system. After analyzing the uClinux's methods of improving real-time ability, a special scheme based on RTAI and RTLINUX is proposed to improve the real-time ability of the bill acceptor system. When the bill is put into the bill acceptor, return signals are formed by the photoelectrical encoder, and they are used as the hardware interrupts by the subsystem to inform a task to acquire the characteristic data of the bill. In this special scheme, in order to increase the processing speed of interrupts and avoid the uClinux's slow processing speed of interrupts, a RTHAL (real-time hardware abstraction layer) which is used to manage interrupts is set between uClinux and hardware. The bill characteristic data acquisition task is separated from OS and put into a separate processing unit. When the bill characteristic data acquisition interrupts appear, the RTHAL gets the interrupts immediately, and stops the operation of uClinux, then informs the processing unit to get the bill characteristic data.