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romable/romable romable/romable ROMABLE.DOC GENERATING ROMABLE FIRMWARE REFERENCES Please refer to the following DCC options: -pi generate position independant code. All code references forced to PC-relative -pr generate residentable position independant code. Unless -mw is specified A4 relative addressing is used for data items. All code references forced to PC-relative. -ma specify that initialized data + bss will be hardwired to a known address -mw specify that initialized data + bss will be hardwired to a known address and all of data + bss occurs somewhere within the first 32KBytes of the address space (0x0000-0x7FFF). Also allows DICE to use A4 as a register variable. -ms const items go into EPROM in local cases -mS const items go into EPROM in local and external cases The following documentation may appear confusing, but only because so many possibilities exist when one intends to put code in ROM. When you are in doubt, it is usually a good idea to write a small test source file, compile it, link it with symbols, and then look at the resulting executable with DOBJ. MAKING ROMABLE PROGRAMS DICE has the capability to generate ROMABLE programs. That is, program binaries that you can use to directly burn an EPROM. When generating ROMABLE code you have more data model options available to you. The basic idea of ROMd code is as follows: ________________ FIXED ADDRESS = EPROM | | | 68000 vectors | const data objects |----------------| | CODE | |----------------| | const DATA | string constants and other | | const items, stays in eprom. |----------------| | read-only copy | | of initialized | this is copied to a working | data | RAM copy by the reset code |________________| ________________ FIXED ADDRESS = RAM | run-time copy | (copied from EPROM by startup) | of initialized | | data | |----------------| (cleared by EPROM startup) | run-time BSS | |________________| From the above you have two basic choices in terms of where your RUN-TIME DATA is based. If your RAM exists in low-memory (0x0000-0x7FFF) you may choose to compile your code to use the ABSOLUTE-WORD addressing mode. This modes takes the same space as the A4-RELATIVE addressing mode yet does not require use of the A4 register and, in fact, the A4 register will then be available for use as a register variable. If you have minimal RAM in low-memory or your DATA+BSS is larger than 32KBytes (yes, that's 32KBytes people, not 64KBytes), then you will have to choose either the formal large-data model or the A4-relative small data model. If you initialized data is over 64KBytes you can still use the small-data model for most objects by using the __far keyword judiciously. NOTE: in all cases you can allocate or generate points for any ram location, this just refers to accesses of declared variables! Pointers are always 32 bits. model options advantages disadvantages absolute-word -mw -ms no need for A4 low 32KBytes only A4 available as reg variable small-data -ma -ms RAM can be anywhere requires A4 must use __geta4 large-data -ma -mD -ms RAM can be anywhere code is larger libs must all be large-data CODE MODEL The CODE MODEL is normally left at PC-relative and should not present a problem. CONST DATA You want to use the -ms option or even the -mS option (see DCC.DOC for the differences). This will place all string constants in EPROM and IN THE CODE SEGMENT, thus this initialized data will NOT take up space in RAM. Any 'const' initialized data will be placed in the code segment and thus in EPROM. Any non-const initialized data will be copied from EPROM into RAM by your reset-startup code. Any tables that you declare that you will never modify should be declared const so they reside in EPROM and do not take up space in RAM. On the otherhand, if your EPROM is running 6 wait states and your RAM is running 0 you might consider not using 'const'.... assuming you have a lot of RAM. When your code is less than 32KBytes big you can use -pi or -pr and should definitely use -mS. When your code is larger than 32KBytes you cannot use -mS unless you are absolutely positive pc-relative const data references do not exceed the word-relative range. RESET VECTOR, DATA MODEL SETUP If your EPROM is mapped into low memory on boot you can declare a vector table by declaring a CONST LONG array as the first data object in the first object module that you link to create the executable: const long ROMVectorTable[] = { InitialSSP, ResetVector, . . . }; Remember, this must be the first data declaration in the first object module!!! If you are using the A4-RELATIVE small-data model you must qualify your ResetVector with the __geta4 type qualifier to set up A4. In most cases you will want ResetVector to point to some assembly which initializes your RAM DATA & BSS before calling C code. The assembly normally looks like this (this would be the second object in the link): ; RESET exception, copy initialized data to RAM and clear ; BSS area before calling rom_main() ; ; Assumes less than 256KBytes of data and 256KBytes of BSS xref __DATA_BAS ; linker generated symbols xref __ABSOLUTE_BAS xref __DATA_LEN xref __BSS_LEN xref _rom_main _ResetVector lea __DATA_BAS,A0 ; ROM data lea __ABSOLUTE_BAS,A1 ; RAM data move.w #__DATA_LEN,D0 ; long words of data bra trentry trloop move.l (A0)+,(A1)+ ; copy EPROM copy to run-time trentry dbf D0,trloop ; RAM copy. move.w #__BSS_LEN,D0 ; long words of BSS (follows data) moveq.l #0,D1 bra trbentry trbloop move.l D1,(A1)+ ; clear run-time RAM trbentry dbf D0,trbloop jmp _rom_main(pc) Where rom_main() is your C main routine qualified with __geta4 (if you are using the A4-RELATIVE data model). Any special items, such as the EPROM getting mapped at reset, must be dealt with as well, usually before the reset code sets up the run-time enviroment. If you are using the ABSOLUTE-WORD data model DO NOT USE __GETA4! Specifically, the -mw option TELLS DICE THAT A4 IS FREE FOR USE AS A NORMAL REGISTER VARIABLE. This gives you an extra register variable if you haven't guessed! EXAMPLE PROGRAM Assume the above assembly module has been assembled and is called 'romc.o'. The following C program is called 'test.c'. In all cases the code may start anywhere. Also, in all cases note that ROMC.O is specified AFTER test in the DCC line (that also serves as the link line). This is because for a standalone product we want our CONST data object that is the ROM VECTOR TABLE to be first. Of course, if you put the ROM VECTOR TABLE in ROMC.A instead of TEST.C then ROMC.A would go first. To put the ROM VECTOR TABLE in ROMC.A it should be the first data object declarations (dc.l's) in the CODE segment. (1) SMALL-DATA-MODEL extern void TrapReset(); extern char SSp[512]; const long RomVectors[] = { (long)SSp, (long)TrapReset }; char SSp[512]; /* our supervisor stack in BSS */ __geta4 void rom_main() { short i; for (;;) { for (i = 0; i < 10000; ++i) { <do something here with i> } } } note, ram can be beyond 64K v COMPILE: dcc test.c romc.o -ma 0x10000 -o t:test -r -v -lrom romable t:test -o t:test.bin -D 0x10000 -C 0x0 burn eprom using test.bin (2) ABSOLUTE WORD DATA MODEL The source code is the same except you do not need __geta4. Here I am assuming RAM starts at, say, 0x2000. void rom_main() { ... } COMPILE: dcc test.c romc.o -mw 0x2000 -o t:test -r -lrom romable t:test -o t:test.bin -D 0x2000 -C 0x0 burn eprom using test.bin (3) ABSOLUTE LONG DATA MODEL The source code is the same as for (2). Here the RAM may start anywhere (also true in (1)). COMPILE: dcc test.c romc.o -ma 0x10080 -o t:test -r -lrom romable t:test -o t:test.bin -D 0x10080 -C 0 burn eprom using test.bin (4) EXAMPLE OF EPROM INITIALLY MAPPED AT 0x0000 BUT REMAPPABLE TO SOMEWHERE ELSE In this case the assembly, ROMC.A, must relocate the EPROM back to where it should be before initializing the data segment. Here your initial CONST data is the EPROM VECTOR TABLE, and your initial non-CONST INITIALIZED data (because BSS gets stuck after all initialized data) will be your RAM VECTOR TABLE. In this example I assume that RAM will be mapped into 0x0000- by the time rom_main() gets called. Compilation depends on the data model. The example below uses the ABSOLUTE WORD data model. extern void TrapReset(); extern char SSp[512]; const long RomVectors[] = { (long)SSp, (long)TrapReset }; long RamVectors[] = { (long)SSp, (long)TrapReset, ... }; char SSp[512]; /* our supervisor stack in BSS */ void rom_main() { ... } In this compilation example I am assuming the RAM will be at 0x0000 and the ROM, say, at 0x20000 (above the 64KBmark) COMPILE: dcc test.c romc.o -mw 0 -o t:test -r -lrom romable t:test -o t:test.bin -D 0 -C 0x20000 burn eprom using test.bin USING ROM.LIB ROM.LIB is generated from LIB/FILES.ROM3LIB and contains those modules from C.LIB that do not declare any variables and are position independant. Modules in the library are entirely position independant. If you use library calls instead of macros in <ctype.h> for ctype functions those are position independant as well ... they use pc-relative to access the lookup tables (which are declared const). Nothing in ROM.LIB declares any data variables. The idea is to link your code with ROM.LIB instead of C.LIB to ensure that incompatible routines are never included by mistake. Warning: If you want position independant code you must compile with -pi or -mS, especially when accessing <ctype.h> macros. Accessing <ctype.h> macros and not using either the above options will result in absolute-code references to ctype's lookup tables. ------------------------------------------------------------------------ MAKING RAM MODULES Generating a binary image for an executable that is meant to run from RAM instead EPROM is relatively easy. In many cases you want only a single copy of the data (instead of two copies as in EPROM modules.. the permanent initialized data in EPROM and the run-time data+bss in RAM). This means that the program is not-reentrant... once an initialized data variable is modified it stays modified. If this is not desireable you can use the same methods as were described for making EPROM code combined with methods (see LIB/AMIGA/C_PR.A) to allocate the data space run-time. If you want to generate resident style modules use the small-data model version in the previous section 'MAKING ROMABLE PROGRAMS' and simply apply the concept of downloading such a module into RAM instead of ROM. It is especially easy when the code is completely position independant because your firmware does not have to deal with relocation at all. This section describes standalone modules with UNsharable code because the code is completely position independant and references only one set of data. ________________ ANY ADDRESS IN RAM |startup | | CODE | |----------------| | initialized | | data | |----------------| | | | BSS | |----------------| The code uses a single PC-relative reference to find the start of the data, then generates the A4 register to point to the data section. NOT A SINGLE 32-BIT REFERENCE EXISTS. WARNING: The module has only one set of data. Once initialized data is modified it stays modified through multiple invocations of the module The advantage of using a position independant module is obvious... you can copy it to any point in ram as-is and then call it! For small 68000 boxes with limited memory this is definite plus as it greatly simplifies the loading mechanism. To create a 100% relocatable module, the code must be less than 32K and the data less than 64K. You must use the -pi option when compiling all source modules, when running dlink, and when running ROMABLE. The -pi option, amoung other things, puts the __ABSOLUTE_BAS and __DATA_BAS linker symbols in the code section. Actually, dlink puts the entire program into a single CODE hunk! dcc -c test.c -pi dlink -pi rampi.o test.o -lrom -o test romable test -o test.bin -pi RAMPI.A is something you have to write, but you do have a template. Take a look at LIB/AMIGA/C_PI.A as an example (also note that LIB/AMIGA/X.A is also required). Remember that the autoinit sections must be entirely supported though not necessarily the autoexit sections, it depends on your application. USING ROM.LIB ROM.LIB is generates from LIB/FILES.ROM3LIB and contains compiler support routines that do not require any RAM. Modules in the library are entirely position independant. If you use library calls instead of macros in <ctype.h> for ctype functions those are position independant as well ... they use pc-relative to access the lookup tables (which are declared const). Nothing in ROM.LIB declares any data variables. The idea is to link your code with ROM.LIB instead of C.LIB to ensure that incompatible routines are never included (instead you get an undefined symbol error from the linker when you make a mistake). Warning: If you want position independant code you must compile with -pi or -mS, especially when accessing <ctype.h> macros. ------------------------------------------------------------------------ ROMABLE exeFile -o outFile [-o outFile2] -C addr -D addr -pi addr: decimal, 0octal, or 0xHEX Romable generates a binary image for an executable compiled under DICE and is normally used to generate a ROMABLE raw binary output file. exeFile input executable linked with dlink -o outFile output binary (unformatted -- raw). If TWO -o options are specified the two output files will have even bytes and odd bytes respectively, which is what you need when you must program two eproms (one on the LSB data lines and one on the MSB data lines) example: -o out1 result: 01 02 03 04 example: -o out1 -o out2 result (out1): 01 03 result (out2): 02 04 -C addr code start address, 0octal, decimal, or 0xHEX -D addr data start address, 0octal, decimal, or 0xHEX -DC place actual data+bss just after code (i.e. the result is intended to be downloaded into RAM, there is no duplicate data in this case). '-D addr' is not specified in this case -pi generate a position independant module. Neither -C or -D are specified in this case, and ROMABLE will warn you have any absolute references. Note that your custom startup code determines how much of __autoinit and __autoexit is to be supported. Note especially that __autoinit0 MUST BE SUPPORTED because DICE will generate __autoinit0 sections to handle 32 bit data relocations run-time. ROMABLE generates a raw output file or files with the EPROM code first, and initialized data after the main code (still in EPROM) which, as has already been described, will be copied to RAM on reset by your startup routine. This startup-copying of initialized data and clearing of BSS makes it extremely easy to use DICE to generate ROMED applications without having to deal with major porting considerations.