Lpc2000

--- In lpc2000@yahoogroups.com, Jan Thogersen <jan@...> wrote:
>
> Hi,
> 
> It's now my second week in the presence of a Phillips ARM processor 
and 
> I must say that it really rock's! However, due to my lack of 
experience 
> with this wonder I face some problems getting the thing to obey all 
my 
> orders :-)
> 
> I really appreciate the effort people are making in this mailing 
list to 
> help each other and when I gain some experience I will do my best 
to 
> repay my debt!
> 
> Playing with the SPI and SSP module left me with a couple of 
questions...
> 
> SPI speed:
> I initialized the SPI module and to my surprise the clock was only 
7.5 
> MHz even though the core was running 60MHz. Then I saw in the 
datasheet 
> that the SPI module only runs at 1/8 of the core speed. Can that 
really 
> be true and why is that? 7.5MHz at max is close to useless in these 
days.
> 
> SSP interrupts:
> In my design I have a DAC connected to the SSP module. The DAC 
needs 24 
> bits for each conversion. Therefore I need to pull the SS low then 
send 
> the 24bits and wait for the SSP modul to enter idle state (Checking 
the 
> busy flag) then raise the SS again. Now I want to get this process 
to 
> run automatically in interrupts. So I need to get an interrupt when 
the 
> SSP is done... But it doesn't seem to be possible, the only flag 
> available is the timeout flag and that is issued 32 clocks after 
the 
> transmission ends. Which leaves me with a bit gab in the 
transmission. 
> Is the timeout flag my only friend in this situation?
> 
> Interrupt problem:
> I got timer vectored interrupts up and running just fine, however 
the 
> SSP just won't request any interrupts. Here is a snippet of my 
code. 
> Maybe it's very obvious what I'm doing wrong, but I can't see it.
> As I said the other interrupts are working just fine, so I really 
can't 
> see why the SSP interrupts won't work.
> I'm using the CrossWorks compiler.
> 
> static void SSP_isr(void) __attribute__ ((interrupt ("IRQ")));
> static void SSP_isr(void) {
>   static uint8 ting;
> 
>   for(;;);
> 
>   VICVectAddr = 0;
> }
> 
> void SSP_Init(void) {
>   SSPCR0 = (0 << 8) | 0x47;  // Set phases and baud rate
>   SSPCR1 = 0x02; // Enable SSP module
>   SSPCPSR = 0x02; // Clock Prescale Register
>   PINSEL1 |= 0x000002A8; // Map the SPI functionality to pins
> 
>   SSPIMSC = SSPIMSC_RORIM |SSPIMSC_RTIM | SSPIMSC_RXIM | 
SSPIMSC_TXIM; 
> // Enable the interrupts
>  
>   VICIntSelect &= ~0x00000800;   // Map SSP to "IRQ"
>   VICIntEnable = 0x00000800;      // Enable the SSP interrupt in 
the VIC
>   VICVectCntl2 = 0x0000002B;     // Map SSP interrupt to VIC slot 2
>   VICVectAddr2 = (unsigned int) SSP_isr; // Assign the interrupt 
handler
> }
> 
> And one last question... is it possible to shift between the ARM 
and 
> thumb mode realtime. Is it possible to make some of my functions in 
> thumb mode and some in ARM mode? Any pragma to control the mode?
> 
> Thanks in advance! Hope that I have made some worthy questions!
> 
> Best regards
>    Jan Thogersen
>

Hi Jan,
Many options on the SSP, but one I have used several times in a 
similar situation is to trigger an interrupt using SS. You can 
connect the SS signal to an external int pin. Not the most elegant 
and it uses an extra pin, but it seperates the interrupt mechanism 
from the SSP module (up to you to decide if that is a good thing in 
your app.)   Also, if you are generating your SS signal from the LPC 
timers you can use the timer interrupts.

Regards,
Ian