17.4.2 BME Decorated LoadsThe functions supported by the BME's decorated loads include two single-bit load-and-{set, clear} operators plus unsigned bit field extracts. For the two load-and-{set, clear}operations, BME converts a single decorated AHB load transaction into a 2-cycle atomicread-modify-write sequence, where the combined read-modify operations are performedin the first AHB data phase, and then the write is performed in the second AHB dataphase as the original read data is returned to the processor core. For an unsigned bit fieldextract, the decorated load transaction is stalled for one cycle in the BME as the data fieldis extracted, then aligned and returned to the processor in the 2nd AHB data phase. Thisis the only decorated transaction that is not an atomic read-modify-write, as it is a simpledata read.A generic timing diagram of a decorated load showing a load-and-set 1-bit operation isshown as follows.x x+1 x+2 x+3next4c.v_wxyznextnext400v_wxyz 400v_wxyz nextnext4c.v_wxyzrdata + 1bitrdata + 1bitnextrdataorig_1bitCYCLE RULERhclkBME AHB Input Busmx_haddrmx_hattrmx_hwritemx_hwdatamx_hrdatamx_hreadyBME AHB Output Bussx_haddrsx_hattrsx_hwritesx_hwdatasx_hrdatasx_hreadyBME States + Datapathcontrol_state_dp1control_state_dp2reg_addr_data_dpFigure 17-7. Decorated load: load-and-set 1-bit field insert timing diagramDecorated load-and-{set, clear} 1-bit operations follow the execution template shown inthe above figure: a 2-cycle read-modify-write operation:Chapter 17 Bit Manipulation Engine (BME)KL04 Sub-Family Reference Manual, Rev. 3.1, November 2012Freescale Semiconductor, Inc. 249
