问答

[align=left]**** Running the ModelSim simulation **** [/align][align=left]D:/altera/13.1/modelsim_ase/win32aloem//vsim -c -do 3biaojue.do [/align][align=left]Reading D:/altera/13.1/modelsim_ase/tcl/vsim/pref.tcl [/align][align=left]# ** Warning: (vish-164) Directory 'D:' specified with envrionment variable $TMPDIR does not exist.[/align] [align=left]# No such file or directory. (errno = ENOENT)[/align] [align=left]** Fatal: Exiting VSIM license process.[/align] [align=left]Error. [/align]

在使用AVR单片机时，发现设置MAIN时钟时需要对CCP寄存器进行解锁操作（4个内指令完成）。在查看了protected_io.S文件后，发现此使用了汇编来解锁以保证能在4个指令周期内完成时钟配置。但是有一个疑问就是，调用protected_write_io函数来操作CCP寄存器时，汇编代码中使用的寄存器为R20和R24为什么不是其他寄存器呢？#include PUBLIC_FUNCTION(protected_write_io) #if defined(__GNUC__) #ifdef RAMPZ out _SFR_IO_ADDR(RAMPZ), r1 // Clear bits 23:16 of Z #endif //为什么使用R24和R22以及R20，为什么不能是其他寄存器。这些寄存器都是protected_write_io函数的形参 [color=#f00000]movw r30, r24 [/color] // Load addr into Z [color=#f00000]out CCP, r22 [/color] // Start CCP handshake [color=#f00000]st Z, r20 [/color] // Write value to I/O register [color=#f00000]ret[/color] // Return to caller #elif defined(__IAR_SYSTEMS_ASM__) # if !defined(CONFIG_MEMORY_MODEL_TINY) && !defined(CONFIG_MEMORY_MODEL_SMALL) \ && !defined(CONFIG_MEMORY_MODEL_LARGE) # define CONFIG_MEMORY_MODEL_SMALL # endif # if defined(CONFIG_MEMORY_MODEL_LARGE) ldi r20, 0 out RAMPZ, r20 // Reset bits 23:16 of Z movw r30, r16 // Load addr into Z # elif defined(CONFIG_MEMORY_MODEL_TINY) ldi r31, 0 // Reset bits 8:15 of Z mov r30, r16 // Load addr into Z # else movw r30, r16 // Load addr into Z # endif # if defined(CONFIG_MEMORY_MODEL_TINY) out CCP, r17 // Start CCP handshake st Z, r18 // Write value to I/O register # elif defined(CONFIG_MEMORY_MODEL_SMALL) out CCP, r18 // Start CCP handshake st Z, r19 // Write value to I/O register # elif defined(CONFIG_MEMORY_MODEL_LARGE) out CCP, r19 // Start CCP handshake st Z, r20 // Write value to I/O register # else # error Unknown memory model in use, no idea how registers should be accessed # endif ret #else # error Unknown assembler #endif END_FUNC(protected_write_io) END_FILE()