Bus error berror indicates a transaction that cannot

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Unformatted text preview: est mode to be supported is that the tester has access to the ASB through a 32-bit bidirectional port. Where a 32-bit bidirectional data bus interface to external memory or peripheral devices exists, this suffices. Where the off-chip data interface is only 16 or 8 bits wide other signals such as address lines are required to give 32 lines for test access. The test interface allows control of the ASB address and data buses using protocols defined on the two test request inputs {TREQA and TREQB) and an address latch and incrementer in the controller. A suitably designed macrocell module can then allow access to all of its interface signals in groups of up to 32 bits. For example, the ARM? macrocell has a 13-bit control and configuration input, a 32-bit data input, a 15-bit status output and 32-bit address and data outputs. The test vectors are applied and the responses sensed following a sequence defined by a finite state automata whose state transitions are controlled by TREQA and TREQB. The AMBA macrocell test methodology may be compared with the JTAG-based methodology proposed in 'Macrocell testing' on page 230. Although perhaps less general, the AMBA approach will reduce test cost due its parallel tester interface. The ASB offers a relatively high-performance on-chip interconnect which suits processor, memory and peripheral macrocells with some built-in interface sophistication. For very simple, low-performance peripherals, the overhead of the interface is too high. The Advanced Peripheral Bus is a simple, static bus which operates as a stub on an ASB to offer a minimalist interface to very simple peripheral macrocells. The bus includes address (PADDR[n:0]\ the full 32 bits are not usually required) and read and write data (PRDATA[m:0] and PWDATA[m:0], where m is 7, 15 or 31) buses which are no wider than necessary for the connected peripherals, a read/write direction indicator (PWRITE), individual peripheral select strobes (PSELx) and a Test interface Advanced Peripheral...
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This document was uploaded on 10/30/2011 for the course CSE 378 380 at SUNY Buffalo.

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