Re: [Sdcc-user] Boot loader

[<fj...@ya...>]

 --- Jean-Christophe Bequart <kv...@gm...> escribió: >
Hello everyone,
> 
> I'm designing software for a 8051 system with an
> external Flash, and 
> would like to implement my firmware in two parts:
> 
> 1) a boot (loader) at address 0x0000,
> 2) the actual application at an upper address (say
> for example 0x1000).
> 
> The whole thing should work following way:
> -> normal use: the boot loader executes and then
> jumps to 0x1000,
> -> firmware update request: the boot loader executes
> following steps:
> 	1) copy the boot loader from flash to xdata RAM,
> 	2) switch the memory spaces code <-> xdata and then
> run from RAM
> 	3) start the firmware update procedure.
> 
> The hardware has a flash from 0x0000 to 0xFFFF in
> code space, and RAM 
> from 0x0000 to 0x7FFF in xdata space. As described
> above, it is possible 
>    to switch the xdata and code memory spaces.
> 
> So now the actual problem (s):
> 
> - 1st problem: the 8051 has all its interrupt
> vectors at 0x03, 0x0B, 
> etc... In the SDCC docs it is stated that when
> compiling with the option 
> --code-loc, the interrupt vector table is is
> relocated to that address. 
> But I guess that in this case, the boot loader has
> to include a jump 
> (probably a ljmp 0x100x in my example) and that in
> this case I have to 
> put this as a small assembler stub like that in the
> boot loader:
> 
> void serial_isr (void) interrupt 4
> 	{
> 		_asm
> 		ljmp	0x1000	(or should it be lcall 0x1000 / reti?)
> 		_endasm;
> 	}
> 
> Now the point: What is if the application and the
> boot loader use their 
> own ISRs? 

I'm working in a similar project and I use the F0 flag
(in PSW register) to execute the bootloader ISR or the
application ISR.

I use the Keil compiler. For example, in a .asm file I
put the following code:


		CSEG AT 02BH
T2_VECTOR:	JB	F0, BOOT_T2
		LJMP	APP_VECTOR + 02BH
BOOT_T2:	AJMP	T2_ISR

The T2_ISR is the bootloader ISR.
APP_VECTOR is the direction where the application
start

At the beginning of the bootloader, the F0 bit must be
set to 1 and before execute the application, the F0
bit must be set to 0.



> I mean, in both cases I use the serial
> port for example...
> The alternative would probably be making the
> application use the boot 
> loader ISRs... but in this case the app. and the
> boot loader must agree 
> on common functions / variables and have to both to
> know their 
> respective addresses. I mean, I could do this
> special thing in assembler 
> but it would be nice to do it in C... Is there a
> possibility to assign 
> particular functions a specific address in code?
> 
> - 2nd problem (it is really one?) I have to complile
> the boot loader 
> using the option --model-small (no xram available!)
> and I plan to 
> compile the application with the option
> --model-large. Should I expect 
> some problems? And then, it is sufficient to put a
> ljmp (or a lcall) at 
> the end of the boot loader so that the main () of
> the application will 
> be executed?
> 
> I'm using SDCC v 2.3.5, 10/18/2003 on a SusE 8.0
> linux machine, mainly 
> for various hobby projects. Normally I use a 8051
> with an on-chip flash 
> and in this case, I don't have this particular boot
> loader problem... 
> But here the hardware is already there (in fact, it
> was formerly all 
> written in assembler, and is currently being
> redesigned).
> 
> Many thanks for reading this long email and for your
> help,
> 
> 
> Jean-Christophe.
> 
> 
> 
>
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