C51: Reserve Memory at Absolute Bank Addresses

Information in this article applies to:

• C51, all Versions
• BL51, all Versions
• LX51, all Versions

QUESTION

I am using the C51 Compiler and µVision with a code banking project. I have a 88KB CODE memory in the chip. The lower 32KB is assigned to the common area, and the rest is for the code banked area. I have 2 banks: one 32 kb and the other is 24 kb.

Is there a way to tell compiler/linker that not all the banks are of the same size?

I need the compiler linker to enforce the size issue in order to know any violations in size.

ANSWER

Yes, you can block the memory usage in the linker as described below:

When using the LX51 Linker/Locater, just enter under Options - LX51 Locate - Reserve: B1:0xE000-B1:0xFFFF. This blocks the memory area 0xE000 - 0xFFFF from being used by other variables.

When using the BL51 Linker/Locater, the solution is a bit more complicated. You can reserve the memory area 0xE000 - 0xFFFF in bank 1 with the following method:

• Add a source module called B1_RESERVE.C with the following content:

  code unsigned char dummy[0x2000];
  

• Enter under Options - BL51 - Misc - Misc: BANK1 (?CO?b1_reserve (0xE000)). This locates dummy to address 0xE000 in bank 1.

• Enter under Options - BL51 - Misc - Overlay: * ! ?CO?b1_reserve. This avoids the linker Warning L16: UNCALLED SEGMENT, IGNORED FOR OVERLAY PROCESS.

MORE INFORMATION

• Refer to RESERVE in the LX51 User's Guide.

SEE ALSO

• LX51: Cannot Locate Segments
• LX51: Locating Program or Variables to Special Areas
• C51: Locating Initialized Variables at Absolute Addresses
• C51: Reserving Memory Accessed With XBYTE and XWORD

Last Reviewed: Thursday, February 25, 2021