It's been suggested that I should provide some more details on this particular problem, so here goes :) The sample code I have is from "IXP1200 Programming" by Erik J. Johnson and Aaron R. Kunze. It's chapter 5's sample, the single-threaded packet counter. This is an excerpt of the uC compiler output. // My comments will in C++ style // Initialize the cntr variable, as GPR a0 ;****** cntr = (__declspec(scratch) unsigned int *)0; immed[cntr_109$2$4:a0, 0, <<0] // Write "0" into the scratchpad memory ;****** *cntr = 0; immed[$0, 0, <<0] scratch[write, $0, cntr_109$2$4:a0, 0, 1], ctx_swap // Call the receive_packet function. Load the return address into a0 ;****** buf_handle = receive_packet(0, 5, &cur_pkt_len); immed[port_num_100_V$ca$2$5:b2, 0, <<0] immed[rfifo_num_100_V$cb$2$5:a2, 5, <<0] br[_receive_packet#], defer[1] load_addr[a0, l_55#] // Increment the packet count in scratch memory. Notice, however, that a0, // the pointer to scratch memory a0 now contains the return address of // label 1_55#, and not a valid pointer into scratch memory. l_55#: ;****** scratch_incr(cntr, no_signal); scratch[incr, --, cntr_109$2$4:a0, 0, 1], no_signal -- Francis