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DMA like behaviour for USB POS device and Host PC

IP.com Disclosure Number: IPCOM000191299D
Original Publication Date: 2009-Dec-28
Included in the Prior Art Database: 2009-Dec-28
Document File: 1 page(s) / 42K

Publishing Venue

IBM

Abstract

Currently the Host PC will send data to the POS device via USB bus. Timing issues such as the host PC send data too fast for the POS Printer to process cause the POS Printer to hang. However if the Host PC sends the data too slow, there are side effects such as inaccurate motor control. POS Printer will have white lines cutting across huge image as data are sent by chunks. Using a data and interrupt pipe of the USB protocol, the POS device can trigger aka interrupt the Host PC for more data to be sent. Upon receiving the interrupt the Host PC will then send the data to the POS device via the data end point.

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DMA like behaviour for USB POS device and Host PC

Using a data and interrupt pipe of the USB protocol, the POS device can trigger aka interrupt the Host PC for more data to be sent. Upon receiving the interrupt the Host PC will then send the data to the POS device via the data end point.

The main advantage of this implementation over the existing implementation is that the POS device knows how much data it can process and using this mechanism it can prevent any overbuffer and/or underbuffer as it is controlling the data transferring speed of the Host PC. This also makes the code on the Host PC to be generic and need not be customized for different POS devices as each device has its own different timing. Even firmware changes can introduce different timing on the same hardware

The Host PC will allocate a block of "virtual" memory that contains the data. It will

1.

has a "virtual" starting memory address of 0 to the size of buffer


The device initiate an interrupt to request a data from Host PC. Using the

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interrupt pipe, the device will request the data by sending the Host PC the start and end memory address of the "virtual" memory to be transferred
The Host PC will use the start and end memory address sent by the device and

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send the memory content (data) to POS device via the data pipe

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