XJDirect — Programming on-chip flash in your processor

Main situations where XJDirect may be required:

• Testing interfaces at their functional speeds.
• High-speed programming of internal/external flash memory.
• Testing interfaces where there is no or insufficient boundary scan access.

These situations are addressed using three subtly different aspects of XJDirect:

• Processor Emulated Test
• Processor Emulated Programming
• Processor Accelerated Programming

Processor Emulated Test (PET)

PET can be used when an interface needs to be operated at its functional speed, or there is insufficient boundary scan access to a device.

Some examples of where PET might be used are:

1. A processor has a DRAM interface but the clock cannot be accessed using boundary scan.
   The internal registers of the processor are accessed to configure the interface to the DRAM and the interface is tested by issuing reads and writes from the processor.
2. A processor has a 1-wire interface which is accessible from boundary scan but the timing requirements are such that the interface cannot be tested using boundary scan. The internal registers of the processor are accessed to configure the 1-wire interface and the processor interface is used to read and write using the 1-wire interface.
3. A processor has a pin which can be configured either in analogue or a digital mode. Boundary scan uses the pin in digital mode but the interface needs to be tested in analogue mode. Using the processor’s internal registers, the pin is configured in analogue mode and then, again using the processor’s internal registers, an analogue value can be read and checked.
4. A processor has a DDR interface which needs to be exercised at speeds greater than can be achieved using boundary scan. The processor’s internal DDR controller is configured and the interface is tested using high speed read and writes which are issued through the processor.
5. The pull-ups and pull-downs of the processor’s I/O pins have to be enabled for the connection test to run correctly. The pins are configured by accessing the internal registers of the processor.

Processor Emulated Programming (PEP)

PEP is used to program both flash internal to a processor and externally connected as a peripheral.

1. Programming internal flash
   In a very similar way to the PET solutions above, the internal registers of the device are accessed and the flash erased, programmed and verified.
2. Programming external flash
   Whilst it may be possible to program external flash using boundary scan, the serial nature of boundary scan can make this time-consuming particularly if the external device is itself a serial device. By accessing the internal registers of a processor, the external peripheral interface can be configured and then used to access the external flash. The external flash can then be programmed and verified at speeds that cannot be achieved using boundary scan.

Processor Accelerated Programming (PAP)

In most cases PET and PEP will give very acceptable performance. However in some cases it is desirable to achieve even faster performance.

Many processors provide mechanisms for communicating with executing code using the JTAG interface. Many also provide very efficient mechanisms for reading and writing memory using the JTAG interface. XJDirect can utilise these facilities to provide very efficient flash programming. XJDirect configures the processor with a temporary application image – effectively turning it into a dedicated flash programmer.  The efficient mechanisms provided by the processor are then used to transfer the programming data to the processor thereby dramatically improving the programming speed.