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Freeing alloc_mem() memory...

Doug Paulsen

Greetings:

In the RL-ARM User's Guide, the example for interrupt_ethernet() __irq includes a call to function alloc_mem() to receive an ethernet frame. Here is an excerpt from the sample:

       /* Flag 0x80000000 to skip sys_error() call when out of memory. */
        frame = alloc_mem (RxLen | 0x80000000);
        /* if 'alloc_mem()' has failed, ignore this packet. */
        if (frame != NULL) {
          dp = (U32 *)&frame->data[0];
          sp = (U32 *)Rx_Desc[idx].Packet;
          for (RxLen = (RxLen + 3) >> 2; RxLen; RxLen--) {
            *dp++ = *sp++;
          }
          put_in_queue (frame);
        }
rel:    if (++idx == NUM_RX_FRAG) idx = 0;
        /* Release frame from EMAC buffer. */
        MAC_RXCONSUMEINDEX = idx;

Note that there appears to be no explicit de-allocation of the memory pointed to by OS_FRAME *frame. Shouldn't there be a complimentary call to function free_mem()?

A search for "alloc_mem()" from my IDE finds a similar interrupt_ethernet() __irq, except this one includes the following code. Note the comment about MMU free packet:

   /* Flag 0x80000000 to skip sys_error() call when out of memory. */
      frame = alloc_mem (RxLen | 0x80000000);

      /* if 'alloc_mem()' has failed, ignore this packet. */
      if (frame != NULL) {
         /* Make sure that block is 4-byte aligned */
         RxLen = (RxLen + 3) >> 2;

         dp = (U32 *)&frame->data[0];
         for (  ; RxLen; RxLen--) {
            *dp++ = LREG (U32, B2_DATA);
         }
         put_in_queue (frame);
      }

      /* MMU free packet. */
      LREG (U16, B2_MMUCR) = MMU_REMV_REL_RX;

There is still no explicit de-allocation of the memory pointed to by "frame". I wonder if the "LREG (U16,..." somehow does this?

The frightening thing is the first example code (with not even a hint of freeing memory) has been running for quite a while. Is this luck or is something else going on?

Thank you for any comments or recommendations.

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