RFC: register new Interrupt Service Routine (ISR) funtions for additional interrupts

[Henk Vergonet]

Dear Litex community,

Question: how to handle additional interrupts in software?
(I don't see currently an generic way of extending this. )
Currently the isr.c only handles the uart.

A possible API might look like:

int set_handler(unsigned int irq, void (*handler)(void));

void (*handler)(void) get_handler(unsigned int irq);

int remove_handler(unsigned int irq);

My hack for the moment is a callback function in the Litex isr routine shown below.

My little hack to extend the isr routine:

diff --git a/litex/soc/software/libbase/isr.c b/litex/soc/software/libbase/isr.c
index ac7a7920..898eb40a 100644
--- a/litex/soc/software/libbase/isr.c
+++ b/litex/soc/software/libbase/isr.c
@@ -191,6 +191,9 @@ void isr(void)
 }
 
 #else
+
+void (*isr_next)(unsigned int irqs) = NULL;
+
 void isr(void)
 {
        __attribute__((unused)) unsigned int irqs;
@@ -203,6 +206,8 @@ void isr(void)
                uart_isr();
 #endif
 #endif
+       if(isr_next)
+               (*isr_next)(irqs);
 }
 #endif

Code snippet using the callback function for my pps core:

extern void (*isr_next)(unsigned int irqs);
    
void isr_pps(unsigned int irqs)
{
  if (irqs & (1 << PPS0_INTERRUPT)) {
     // handle stuff
  }
}

static void pps_init(void) {
  isr_next = &isr_pps;
  irq_setmask(irq_getmask() | (1 << PPS0_INTERRUPT));
  pps0_ev_enable_write(1);
}

[AndrewD]

There is another pr for a different approach to this.
I've got a more traditional irq handler registration (proof of concept) in our tree I've been meaning to push for discussion.

[Henk Vergonet]

Now made obsolete by the pull request Andrew is working on. #1815
Thanks!