Writing constant to ROM

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Read-Only Author Kiah Hion Tang Posted 8-Feb-2001 09:04 GMT Toolset None	Writing constant to ROM Kiah Hion Tang Maybe this is a simple question, but I just couldn't figure it out. Can someone tell me how to place a constant variable into the specific ROM area? I would like to be able to set a constant value at a particualr ROM area and use a pointer to get it whenever I need it. Cheers, Tang

Read-Only Author Andrew Neil Posted 8-Feb-2001 11:36 GMT Toolset None	RE: Writing constant to ROM Andrew Neil unfortunately, the _at_ keyword can't be used with initialisation. How about code const unsigned char fred = 0xaa; and then using the linker to fix the location? you'd probably need to define 'fred' such that it was in a segment of its own?

Read-Only Author Kiah Hion Tang Posted 8-Feb-2001 11:43 GMT Toolset None	RE: Writing constant to ROM Kiah Hion Tang How to use linker to fix the location?

Read-Only Author Andrew Neil Posted 8-Feb-2001 12:10 GMT Toolset None	RE: Writing constant to ROM Andrew Neil Dunno - I'm afraid you'll have to look that up for yourself in the manuals (which are all in PDF format on the free CD, and can be accessed via the Books tab in the uVision Project window): Look in the C51 manual for where it describes C51's segment naming & usage conventions, then look in the Assembler/Utilities manual for how to locate a specific segment at a specific address. Or try searching the Keil knowledge base, http://www.keil.com/search.asp Or, as your E-Mail appears to be at the University of Warwick, can you just pop over and ask the very nice people at Hitex? ;-)

Read-Only Author Kiah Hion Tang Posted 8-Feb-2001 12:14 GMT Toolset None	RE: Writing constant to ROM Kiah Hion Tang Ha.. :)) good suggestion. Hitex is a good source of knowledge.

Read-Only Author Jon Ward Posted 8-Feb-2001 17:10 GMT Toolset None	RE: Writing constant to ROM Jon Ward Here is a link to the knowledgebase atricle that describes how to do this. http://www.keil.com/support/docs/301.htm Jon

Read-Only Author Kiah Hion Tang Posted 8-Feb-2001 17:22 GMT Toolset None	RE: Writing constant to ROM Kiah Hion Tang Exactly what I am looking for. CHEERS!!

Read-Only Author Doug Hewett Posted 22-Feb-2001 18:45 GMT Toolset None	RE: Writing constant to ROM Doug Hewett Please see my latest posting re this issue. It differs slightly from your example. Specifically: User's guide, 01.97, C compiler C51 on page 63 'explicitly defined memory types' recommends a syntax. The Utilities guide, 04.95, page 119, has a different syntax in files c_mess0.c, c_mess1.c. the utilities guide contradicts the recommendation in the user's guide. Yet the 'preferred' method in the C51 compiler will NOT work. You must use the 'obsolete' method of the Utilities guide. (1) Please explain. (2) What is correct syntax for: const unsigned char code *MyArray[NumberFruits] = {"apple,"banana","cherry"};

Read-Only Author Mark Odell Posted 8-Feb-2001 18:23 GMT Toolset None	RE: Writing constant to ROM Mark Odell I still dream of this construct: const unsigned char code magicNum _at_ 0x8000 = 0xAA; I can dream. - Mark

Read-Only Author Andrew Neil Posted 9-Feb-2001 00:28 GMT Toolset None	RE: Writing constant to ROM Andrew Neil and why ever not?

Read-Only Author Franc Urbanc Posted 9-Feb-2001 20:03 GMT Toolset None	RE: Writing constant to ROM Franc Urbanc Mark, your dream has become true in C251 v2.14 already. I use it to store the Revision code of the application. Franc

Read-Only Author Mark Odell Posted 10-Feb-2001 01:16 GMT Toolset None	RE: Writing constant to ROM Mark Odell Impossible! How could that be? How could C251 get that feature before C51? C51 is probably used 10 to 1 over C251. Unfare! I declare a 10 yard penalty, repeat second down (Man it's great to have the XFL now. February can be so cold without football). - Mark

Read-Only Author Franc Urbanc Posted 10-Feb-2001 17:19 GMT Toolset None	RE: Writing constant to ROM Franc Urbanc Here is how I do it: 1. I define the code version in the header file: /********************* FIRMWARE CODE VERSION ***************************/ #define CODE_VERSION 3 // 10 is version 1.0 In the source module, I put the variable into the codespace (into the gap just behind external interrupt 0 LJMP instruction): unsigned char code version _at_ 0x0006 = CODE_VERSION; This value can be accessed by the system flash upgrade software at location 6 of the code region 0xFF. So The software displays the new version at file opening time and before actual downloading to the target system. Franc

Read-Only Author Andrew Neil Posted 10-Feb-2001 20:17 GMT Toolset None	RE: Writing constant to ROM Andrew Neil unsigned char code version _at_ 0x0006 = CODE_VERSION; But that's not allowed - you can't use an initialiser with the _at_ keyword. See p79 in the C51 User's Guide, 03.2000: "The following restrictions apply to absolute variable location: 1. Absolute variables cannot be initialized. 2. Functions and variables of type bit cannot be located at an absolute address."

Read-Only Author Mark Odell Posted 12-Feb-2001 01:36 GMT Toolset None	RE: Writing constant to ROM Mark Odell That's what I thought. I'm still dreaming of this feature for the C51. - Mark

Read-Only Author Russell Anderson Posted 25-Feb-2005 14:37 GMT Toolset C51	RE: Writing constant to ROM Russell Anderson Why does Keil have this restriction? You can do this with Raisonance and I would like to have my code be compatible with both. For Raisonance you just use: at 0x803d code char my_char = 0x55; I don't need to have a variable name created, but I would like to be able to set a byte that configures the hardware. This is a hardware configuration byte that needs to be programmed when the program is loaded. If I understand correctly there is no way to add a single statement to the Keil C program for this function. I have to link an assembly language file to do that with Keil. Is that correct?

Read-Only Author Stefan Duncanson Posted 25-Feb-2005 15:12 GMT Toolset C51	RE: Writing constant to ROM Stefan Duncanson "Why does Keil have this restriction?" Although it seems a simple enough addition apparently it will involve a major rewrite of part of the compiler. You can put the 'variable' in its own 'C' source file then link that as a 'user segment'. There's an example in the knowledgebase somewhere.

Read-Only Author Andrew Neil Posted 9-Feb-2001 00:30 GMT Toolset None	RE: Writing constant to ROM Andrew Neil Thanks for that, Jon. As you can probably tell, I've done this before - but not yet with the Keil toolset. I'm sure it'll come in handy.

Read-Only Author Doug Hewett Posted 22-Feb-2001 18:49 GMT Toolset None	RE: Writing constant to ROM Doug Hewett this is a copy of my posting today. If I follow the recommendation of the compiler manual, the linker puts the table of pointers into xdata. I must use the non-preferred method (per the utilities manual). Thanks. By the way, I can't find the pdf for the utilites manual. Is there one? === paste === User's guide, 01.97, C compiler C51 on page 63 'explicitly defined memory types' recommends a syntax. The Utilities guide, 04.95, page 119, has a different syntax in files c_mess0.c, c_mess1.c. the utilities guide contradicts the recommendation in the user's guide. Yet the 'preferred' method in the C51 compiler will NOT work. You must use the 'obsolete' method of the Utilities guide. (1) Please explain. (2) What is correct syntax for: const unsigned char code *MyArray[NumberFruits] = {"apple,"banana","cherry"};

Read-Only Author Drew Davis Posted 25-Feb-2005 23:45 GMT Toolset None	RE: Writing constant to ROM Drew Davis const unsigned char code MyArray[NumberFruits] = {"apple,"banana","cherry"};* There's one occurrence of "code" in this definition, to the left of the . That means it applies to the "unsigned char". So, this is a table of pointers (in RAM) that point to characters in code memory. If you want the pointers themselves in code memory, you need to specify that as well: const unsigned char code code MyArray...

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