Lpc2000

Hi, all!

First of all I want to thank everybody in this group. The amount and 
quality of help I'm receiving from you guys is extraordinary. I 
sincerely hope I can contribute helping others in due time.

I am doing some IRQ compilation tests with GCC and the __attribute__ 
((interrupt("IRQ")) syntax. Apparently the code doesn't seem to 
save/restore all the registers I expected. In particular, it doesn't 
seem to save spsr. Also, only general registers r1-r4 are saved 
before calling an external function. I have the following questions:

* Saving spsr is only needed for reentrant IRQs?
* Perhaps saving only r1-r4 is a convention, and functions should 
always save by themselves any other general registers they may use?
* Should I worry or this is perfectly normal and *safe*?

Thanks in advance.

Guille

void Uart0Service(void) __attribute__ ((interrupt("IRQ"));

void Uart0Service(void)
{
18f0:  e24ee004  sub    lr, lr, #4 ; 0x4
18f4:  e92d500f  stmdb  sp!, {r0, r1, r2, r3, ip, lr}
unsigned char temp_id;
temp_id = U0IIR;
    18f8:  e3a03903   mov  r3, #49152   ; 0xc000
    18fc:  e283328e   add  r3, r3, #-536870904  ; 0xe0000008
    1900:  e5d32000   ldrb  r2, [r3]
switch(temp_id & IDENT_MASK) {
    1904:  e202200e   and  r2, r2, #14  ; 0xe
case DATA_AVAILABLE:
case DATA_TIMEOUT:
receive();
break;
case TRANSMIT_AVAILABLE:
transmit();
default:
break;
}
    /* case DATA_AVAILABLE */
    1908:  e3520004   cmp  r2, #4       ; 0x4
    190c:  0a000005   beq  1928 <Uart0Service+0x38>

    /* case DATA_TIMEOUT */
    1910:  e352000c   cmp  r2, #12      ; 0xc
    1914:  0a000003   beq  1928 <Uart0Service+0x38>

    /* case [not] TRANSMIT_AVAILABLE */
    1918:  e3520002   cmp  r2, #2       ; 0x2
    191c:  18fd900f   ldmneia  sp!, {r0, r1, r2, r3, ip, pc}^

    1920:  ebfffa69   bl  2cc <transmit>
    1924:  e8fd900f   ldmia  sp!, {r0, r1, r2, r3, ip, pc}^

    1928:  ebfffa75   bl  304 <receive>
    192c:  e8fd900f   ldmia  sp!, {r0, r1, r2, r3, ip, pc}^
}

Shouldn't this code also save spsr? Or perhaps this is only needed 
for reentrant IRQs?

Guille