Background Debug Mode (BDM) InterfaceMCF5253 Reference Manual, Rev. 120-26 Freescale Semiconductorbe disabled during the read/write process so the exact bit-wise eMAC register contents are accessed. Forexample, a BDM read of an accumulator (ACCx) requires the following sequence:Bdm Read ACCx (rcreg macsr; // read current macsr contents & savewcreg #0,macsr; // disable all rounding modesrcreg ACCx; // read the desired accumulatorwcreg #saved_data,macsr; // restore the original macsrLikewise to write an accumulator register, the following BDM sequence is needed:Bdm Write ACCx (rcreg macsr; // read current macsr contents & savewcreg #0,macsr; // disable all rounding modeswcreg #data,ACCx; // write the desired accumulatorwcreg #saved_data,macsr; // restore the original macsr)Additionally, writes to the accumulator extension registers must be performed after the correspondingaccumulators are updated because a write to any accumulator alters the corresponding extension registercontents.Command Sequence:Figure 20-27. Read Control Register Command SequenceOperand Data:The single operand is the 32-bit Rc control register select field.Result Data:The contents of the selected control register are returned as a longword value. The data is returned mostsignificant word first. For those control registers with widths less than 32 bits, only the implementedportion of the register is guaranteed to be correct. The remaining bits of the longword are undefined.20.4 Real-Time Debug SupportThe ColdFire Family provides support for the debug of real-time applications. For these types ofembedded systems, the processor cannot be halted during debug, but must continue to operate. Thefoundation of this area of debug support is that while the processor cannot be halted to allow debugging,the system can generally tolerate small intrusions into the real-time operation.The debug module provides a number of hardware resources to support various hardware breakpointfunctions. Specifically, three types of breakpoints are supported: PC with mask, operand address range,and data with mask. These three basic breakpoints can be configured into one- or two-level triggers withMS ADDR“NOT READY”MS ADDR“NOT READY”READREGISTERXXX“NOT READY”XXXMS RESULTXXXBERRNEXT CMDLS RESULTNEXT CMD“NOT READY”RCREG??? CONTROL
