Cortex-A8 R2P2.pdf - ARM Information Center

NEON and VFP Programmer’s Model13.3 Short vectorsThe VFPv3 architecture supports execution of short vector instructions of up to eightoperations on single-precision data and up to four operations on double-precision data.The register file is especially suited for short vector operations. The foursingle-precision and eight double-precision register banks function as four hardwarecircular queues.13.3.1 About register banksAs Figure 13-2 on page 13-7 shows, the register file is divided into four banks witheight registers in each bank for single-precision instructions and eight banks with fourregisters per bank for double-precision instructions. CDP instructions access the banksin a circular manner. Load and store multiple instructions do not access the registers ina circular manner but treat the register file as a linearly ordered structure.The VFPv3 architecture adds 16 double-precision registers, making use of theadditional register addressing bits currently used to specify single-precision registers.The first 16 registers, D0 through D15, in the NEON register file provides the samefunctionality as the register file defined in the VFPv2 architecture. VFPv3 adds 16 newdouble-precision registers, D16 through D31, which provides a second set of 16double-precision registers. These registers behave in vector mode in an identicalmanner to the lower 16 registers, with bank 4 specified as registers D16-D19, bank 5specified as registers D20-D23, bank 6 specified as registers D24-D27, and bank 7specified as D28-D31. Bank 4 of the second set of registers has the same characteristicswhen used in short vector instructions as bank 0 of the first set of registers.Short vector operations on double-precision data support vector lengths of two throughfour iterations. The additional registers provides the capability to double-bufferdouble-precision operations in a similar way as is available for single-precisionoperations.See the ARM Architecture Reference Manual for more information on VFP addressingmodes.13-6 Copyright © 2006-2008 ARM Limited. All rights reserved. ARM DDI 0344E