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Hello,
I am new to embedded programming, particularly C, and I am trying to write bytes to code memory, within my already executing code. The purpose is to see if I can write a program to program memory within a program. I believe that is sometimes called a boot loader.
Here is what I have: (It's a simple approach)
#include "REG51XC2.h" #include <string.h> unsigned char code code_buffer [16] _at_ 0x0B00; unsigned char byte = 0x11; unsigned char * bytep = &byte; void main(void) { memcpy(code_buffer, bytep, sizeof(code_buffer)); while(1); }
What I am trying to do is assign some space in program memory (location 0x0B00) and write a byte there using the method "memcpy".
When I run my emulation, I can see in the disassembler that no where does it use the command "MOVC" which I know to be the assembly way of writing to code memory.
9: void main(void) 10: { 11: memcpy(code_buffer, bytep, sizeof(code_buffer)); C:0x0982 7800 MOV R0,#0x00 C:0x0984 7C0B MOV R4,#byte(0x0B) C:0x0986 7DFF MOV R5,#0xFF C:0x0988 AB08 MOV R3,bytep(0x08) C:0x098A AA09 MOV R2,0x09 C:0x098C A90A MOV R1,0x0A C:0x098E 7E00 MOV R6,#0x00 C:0x0990 7F10 MOV R7,#0x10 C:0x0992 1208D0 LCALL C?COPY(C:08D0) 12: while(1);
The one good thing, though, is that the assignment of "code_buffer" was successful in putting placing it at 0x0B00.
C:0x0AFF 00 NOP code_buffer: C:0x0B00 00 NOP C:0x0B01 00 NOP C:0x0B02 00 NOP
So what my understanding is, is memcpy will allow me to copy values to data memory (internal or external) but not program memory.
With this in mind, does that mean I will be writing a version of the "memcpy" function in assembly to get the data into program memory, or is there another function in C I could use? If so, is there any material I can reference or some code I could use to implement the function above?
I appreciate any help,
Max
Well, if they say that, then get them to show you how!
But that would be a completely non-standard implementation of the 8051 instruction set - so you would need a special compiler that can generate this bastardised code.
Keil does support some extensions to the standard architecture - check here: http://www.keil.com/support/man/docs/c51/c51_dv_8051deriv.htm
See also: http://www.keil.com/support/man/docs/c51/c51_cm_dirlist.htm
Yes - as you are relying on some very specific, non-standard features of that core.
I solved my problem.
MOV PCON, #10h MOV DPTR, #0B00h MOV A, #11h MOVX @DPTR, A
This will move immediate value 0x11 to program memory location 0B00. And yes I know I am relying on specific extensions to the microprocessor (it is developed by CAST Inc.), that was the rational for choosing this microprocessor.
Actually, as far as the 8051 core is concerned, it moves the value to XDATA memory - that is the definition of the MOVx instruction.
You are relying on some external hardware trickery to map that XDATA address into your CODE space.
The good thing here is tht you can do it just as well in 'C' - you don't need any special assembler magic.
We could do the same with the late Triscend E5 - simply update the mapping registers which controlled the mapping of the 8051 core's XDATA and CODE spaces to the external, linear physical address space.
Note also that updating Flash (nothing to do with 8051) is not as simple as just a write operation - a previous erase is generally required...
Probably more precise to say, "... map that XDATA address into the same physical address that your CODE space is mapped into"
Maybe something like this
+----------+ | Physical | | | | | +-------+ | | | CODE | | | | | | | +-------+ | | | | | XDATA | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | +-------+ | | | | | | | | | | +-------+ | | | | | | | | +----------+
The core is just the core, remember this is a soft-core put onto an FPGA, which is different from a DIP chip 8051 for example.
Below I have posted a verbatim copy of what the user manual says, which states that I am actually placing 0x11 into real program memory space. Setting the pwm bit changes the function of MOVX.
The previous erase may be something I need to consider when I begin to implement the code, but I will find a way to make it work.
2.3.5 Program memory write mode The Program Memory Write mode allows full access to the program memory address space. The Program Memory Write feature is an extension to the 8051 instruction set but does not require modification of the standard code. It is enabled using parameter called PMW_IMPLEMENT=1 (0=disabled).
Table 9. Program Memory Write Configuration PMW_IMPLEMENT Action 0 Program Memory Write disabled (“pmw” bit of “pcon” not implemented) 1 (default) Program Memory Write can be enabled by setting “pmw” bit of “pcon” register The MOVX instructions perform one of two actions depending on the state of “pmw” bit (pcon.4). The “pmw” bit selects the standard or advanced behavior of the microcontroller during execution of MOVX instruction. When the “pmw” is cleared or after reset, MOVX instructions allow read/write access to external data memory space. The software can set the “pmw” bit to enable access to program memory space. Once the “pmw” bit is set, MOVX data memory instructions become MOVX program memory instructions with 8 or 16-bit addressing modes. The software clears the “pmw” bit to switch back to normal MOVX behavior. Setting or clearing the “pmw” bit does not influence the execution of MOVC instruction and it does not change the behavior of program memory reading.