| #include <math.h> |
| #include "util.h" |
| #include "vpr_types.h" |
| #include <assert.h> |
| #include "globals.h" |
| #include "rr_graph_util.h" |
| #include "rr_graph_area.h" |
| |
| |
| /************************ Subroutines local to this module *******************/ |
| |
| static void count_bidir_routing_transistors(int num_switch, |
| float R_minW_nmos, |
| float R_minW_pmos); |
| |
| static void count_unidir_routing_transistors(t_segment_inf * segment_inf, |
| float R_minW_nmos, |
| float R_minW_pmos); |
| |
| static float get_cblock_trans(int *num_inputs_to_cblock, |
| int max_inputs_to_cblock, |
| float trans_cblock_to_lblock_buf, |
| float trans_sram_bit); |
| |
| static float *alloc_and_load_unsharable_switch_trans(int num_switch, |
| float trans_sram_bit, |
| float R_minW_nmos); |
| |
| static float *alloc_and_load_sharable_switch_trans(int num_switch, |
| float trans_sram_bit, |
| float R_minW_nmos, |
| float R_minW_pmos); |
| |
| static float trans_per_buf(float Rbuf, |
| float R_minW_nmos, |
| float R_minW_pmos); |
| |
| static float trans_per_mux(int num_inputs, |
| float trans_sram_bit, |
| float pass_trans_area); |
| |
| static float trans_per_R(float Rtrans, |
| float R_minW_trans); |
| |
| |
| /*************************** Subroutine definitions **************************/ |
| |
| |
| void |
| count_routing_transistors(enum e_directionality directionality, |
| int num_switch, |
| t_segment_inf * segment_inf, |
| float R_minW_nmos, |
| float R_minW_pmos) |
| { |
| |
| /* Counts how many transistors are needed to implement the FPGA routing * |
| * resources. Call this only when an rr_graph exists. It does not count * |
| * the transistors used in logic blocks, but it counts the transistors in * |
| * the input connection block multiplexers and in the output pin drivers and * |
| * pass transistors. NB: this routine assumes pass transistors always * |
| * generate two edges (one forward, one backward) between two nodes. * |
| * Physically, this is what happens -- make sure your rr_graph does it. * |
| * * |
| * I assume a minimum width transistor takes 1 unit of area. A double-width * |
| * transistor takes the twice the diffusion width, but the same spacing, so * |
| * I assume it takes 1.5x the area of a minimum-width transitor. */ |
| if(directionality == BI_DIRECTIONAL) |
| { |
| count_bidir_routing_transistors(num_switch, R_minW_nmos, |
| R_minW_pmos); |
| } |
| else |
| { |
| assert(directionality == UNI_DIRECTIONAL); |
| count_unidir_routing_transistors(segment_inf, R_minW_nmos, |
| R_minW_pmos); |
| } |
| } |
| |
| void |
| count_bidir_routing_transistors(int num_switch, |
| float R_minW_nmos, |
| float R_minW_pmos) |
| { |
| |
| /* Tri-state buffers are designed as a buffer followed by a pass transistor. * |
| * I make Rbuffer = Rpass_transitor = 1/2 Rtri-state_buffer. * |
| * I make the pull-up and pull-down sides of the buffer the same strength -- * |
| * i.e. I make the p transistor R_minW_pmos / R_minW_nmos wider than the n * |
| * transistor. * |
| * * |
| * I generate two area numbers in this routine: ntrans_sharing and * |
| * ntrans_no_sharing. ntrans_sharing exactly reflects what the timing * |
| * analyzer, etc. works with -- each switch is a completely self contained * |
| * pass transistor or tri-state buffer. In the case of tri-state buffers * |
| * this is rather pessimisitic. The inverter chain part of the buffer (as * |
| * opposed to the pass transistor + SRAM output part) can be shared by * |
| * several switches in the same location. Obviously all the switches from * |
| * an OPIN can share one buffer. Also, CHANX and CHANY switches at the same * |
| * spot (i,j) on a single segment can share a buffer. For a more realistic * |
| * area number I assume all buffered switches from a node that are at the * |
| * *same (i,j) location* can share one buffer. Only the lowest resistance * |
| * (largest) buffer is implemented. In practice, you might want to build * |
| * something that is 1.5x or 2x the largest buffer, so this may be a bit * |
| * optimistic (but I still think it's pretty reasonable). */ |
| |
| |
| int *num_inputs_to_cblock; /* [0..num_rr_nodes-1], but all entries not */ |
| |
| /* corresponding to IPINs will be 0. */ |
| |
| boolean *cblock_counted; /* [0..max(nx,ny)] -- 0th element unused. */ |
| float *shared_buffer_trans; /* [0..max_nx,ny)] */ |
| float *unsharable_switch_trans, *sharable_switch_trans; /* [0..num_switch-1] */ |
| |
| t_rr_type from_rr_type, to_rr_type; |
| int from_node, to_node, iedge, num_edges, maxlen; |
| int iswitch, i, j, iseg, max_inputs_to_cblock; |
| float input_cblock_trans, shared_opin_buffer_trans; |
| const float trans_sram_bit = 6.; |
| |
| /* Two variables below are the accumulator variables that add up all the * |
| * transistors in the routing. Make doubles so that they don't stop * |
| * incrementing once adding a switch makes a change of less than 1 part in * |
| * 10^7 to the total. If this still isn't good enough (adding 1 part in * |
| * 10^15 will still be thrown away), compute the transistor count in * |
| * "chunks", by adding up inodes 1 to 1000, 1001 to 2000 and then summing * |
| * the partial sums together. */ |
| |
| double ntrans_sharing, ntrans_no_sharing; |
| |
| |
| /* Buffers from the routing to the ipin cblock inputs, and from the ipin * |
| * cblock outputs to the logic block, respectively. Assume minimum size n * |
| * transistors, and ptransistors sized to make the pull-up R = pull-down R. */ |
| |
| float trans_track_to_cblock_buf; |
| float trans_cblock_to_lblock_buf; |
| |
| |
| ntrans_sharing = 0.; |
| ntrans_no_sharing = 0.; |
| max_inputs_to_cblock = 0; |
| |
| /* Assume the two buffers below are 4x minimum drive strength (enough to * |
| * drive a fanout of up to 16 pretty nicely -- should cover a reasonable * |
| * wiring C plus the fanout. */ |
| |
| trans_track_to_cblock_buf = |
| trans_per_buf(R_minW_nmos / 4., R_minW_nmos, R_minW_pmos); |
| |
| trans_cblock_to_lblock_buf = |
| trans_per_buf(R_minW_nmos / 4., R_minW_nmos, R_minW_pmos); |
| |
| num_inputs_to_cblock = (int *)my_calloc(num_rr_nodes, sizeof(int)); |
| |
| maxlen = max(nx, ny) + 1; |
| cblock_counted = (boolean *) my_calloc(maxlen, sizeof(boolean)); |
| shared_buffer_trans = (float *)my_calloc(maxlen, sizeof(float)); |
| |
| unsharable_switch_trans = |
| alloc_and_load_unsharable_switch_trans(num_switch, trans_sram_bit, |
| R_minW_nmos); |
| |
| sharable_switch_trans = |
| alloc_and_load_sharable_switch_trans(num_switch, trans_sram_bit, |
| R_minW_nmos, R_minW_pmos); |
| |
| for(from_node = 0; from_node < num_rr_nodes; from_node++) |
| { |
| |
| from_rr_type = rr_node[from_node].type; |
| |
| switch (from_rr_type) |
| { |
| |
| case CHANX: |
| case CHANY: |
| num_edges = rr_node[from_node].num_edges; |
| |
| for(iedge = 0; iedge < num_edges; iedge++) |
| { |
| |
| to_node = rr_node[from_node].edges[iedge]; |
| to_rr_type = rr_node[to_node].type; |
| |
| switch (to_rr_type) |
| { |
| |
| case CHANX: |
| case CHANY: |
| iswitch = |
| rr_node[from_node].switches[iedge]; |
| |
| if(switch_inf[iswitch].buffered) |
| { |
| iseg = |
| seg_index_of_sblock(from_node, |
| to_node); |
| shared_buffer_trans[iseg] = |
| max(shared_buffer_trans[iseg], |
| sharable_switch_trans |
| [iswitch]); |
| |
| ntrans_no_sharing += |
| unsharable_switch_trans |
| [iswitch] + |
| sharable_switch_trans |
| [iswitch]; |
| ntrans_sharing += |
| unsharable_switch_trans |
| [iswitch]; |
| } |
| else if(from_node < to_node) |
| { |
| |
| /* Pass transistor shared by two edges -- only count once. * |
| * Also, no part of a pass transistor is sharable. */ |
| |
| ntrans_no_sharing += |
| unsharable_switch_trans |
| [iswitch]; |
| ntrans_sharing += |
| unsharable_switch_trans |
| [iswitch]; |
| } |
| break; |
| |
| case IPIN: |
| num_inputs_to_cblock[to_node]++; |
| max_inputs_to_cblock = |
| max(max_inputs_to_cblock, |
| num_inputs_to_cblock[to_node]); |
| |
| iseg = |
| seg_index_of_cblock(from_rr_type, |
| to_node); |
| |
| if(cblock_counted[iseg] == FALSE) |
| { |
| cblock_counted[iseg] = TRUE; |
| ntrans_sharing += |
| trans_track_to_cblock_buf; |
| ntrans_no_sharing += |
| trans_track_to_cblock_buf; |
| } |
| break; |
| |
| default: |
| printf |
| ("Error in count_routing_transistors: Unexpected \n" |
| "connection from node %d (type %d) to node %d (type %d).\n", |
| from_node, from_rr_type, to_node, |
| to_rr_type); |
| exit(1); |
| break; |
| |
| } /* End switch on to_rr_type. */ |
| |
| } /* End for each edge. */ |
| |
| /* Now add in the shared buffer transistors, and reset some flags. */ |
| |
| if(from_rr_type == CHANX) |
| { |
| for(i = rr_node[from_node].xlow - 1; |
| i <= rr_node[from_node].xhigh; i++) |
| { |
| ntrans_sharing += shared_buffer_trans[i]; |
| shared_buffer_trans[i] = 0.; |
| } |
| |
| for(i = rr_node[from_node].xlow; |
| i <= rr_node[from_node].xhigh; i++) |
| cblock_counted[i] = FALSE; |
| |
| } |
| else |
| { /* CHANY */ |
| for(j = rr_node[from_node].ylow - 1; |
| j <= rr_node[from_node].yhigh; j++) |
| { |
| ntrans_sharing += shared_buffer_trans[j]; |
| shared_buffer_trans[j] = 0.; |
| } |
| |
| for(j = rr_node[from_node].ylow; |
| j <= rr_node[from_node].yhigh; j++) |
| cblock_counted[j] = FALSE; |
| |
| } |
| break; |
| |
| case OPIN: |
| num_edges = rr_node[from_node].num_edges; |
| shared_opin_buffer_trans = 0.; |
| |
| for(iedge = 0; iedge < num_edges; iedge++) |
| { |
| iswitch = rr_node[from_node].switches[iedge]; |
| ntrans_no_sharing += |
| unsharable_switch_trans[iswitch] + |
| sharable_switch_trans[iswitch]; |
| ntrans_sharing += |
| unsharable_switch_trans[iswitch]; |
| |
| shared_opin_buffer_trans = |
| max(shared_opin_buffer_trans, |
| sharable_switch_trans[iswitch]); |
| } |
| |
| ntrans_sharing += shared_opin_buffer_trans; |
| break; |
| |
| default: |
| break; |
| |
| } /* End switch on from_rr_type */ |
| } /* End for all nodes */ |
| |
| free(cblock_counted); |
| free(shared_buffer_trans); |
| free(unsharable_switch_trans); |
| free(sharable_switch_trans); |
| |
| /* Now add in the input connection block transistors. */ |
| |
| input_cblock_trans = get_cblock_trans(num_inputs_to_cblock, |
| max_inputs_to_cblock, |
| trans_cblock_to_lblock_buf, |
| trans_sram_bit); |
| |
| free(num_inputs_to_cblock); |
| |
| ntrans_sharing += input_cblock_trans; |
| ntrans_no_sharing += input_cblock_trans; |
| |
| printf("\nRouting area (in minimum width transistor areas):\n"); |
| printf |
| ("Assuming no buffer sharing (pessimistic). Total: %#g Per logic tile: " |
| "%#g\n", ntrans_no_sharing, ntrans_no_sharing / (float)(nx * ny)); |
| printf |
| ("Assuming buffer sharing (slightly optimistic). Total: %#g Per logic tile: " |
| "%#g\n\n", ntrans_sharing, ntrans_sharing / (float)(nx * ny)); |
| } |
| |
| void |
| count_unidir_routing_transistors(t_segment_inf * segment_inf, |
| float R_minW_nmos, |
| float R_minW_pmos) |
| { |
| boolean *cblock_counted; /* [0..max(nx,ny)] -- 0th element unused. */ |
| int *num_inputs_to_cblock; /* [0..num_rr_nodes-1], but all entries not */ |
| |
| /* corresponding to IPINs will be 0. */ |
| |
| t_rr_type from_rr_type, to_rr_type; |
| int i, j, iseg, from_node, to_node, iedge, num_edges, maxlen; |
| int max_inputs_to_cblock, cost_index, seg_type, switch_type; |
| float input_cblock_trans; |
| const float trans_sram_bit = 6.; |
| |
| /* Two variables below are the accumulator variables that add up all the * |
| * transistors in the routing. Make doubles so that they don't stop * |
| * incrementing once adding a switch makes a change of less than 1 part in * |
| * 10^7 to the total. If this still isn't good enough (adding 1 part in * |
| * 10^15 will still be thrown away), compute the transistor count in * |
| * "chunks", by adding up inodes 1 to 1000, 1001 to 2000 and then summing * |
| * the partial sums together. */ |
| |
| double ntrans; |
| |
| |
| /* Buffers from the routing to the ipin cblock inputs, and from the ipin * |
| * cblock outputs to the logic block, respectively. Assume minimum size n * |
| * transistors, and ptransistors sized to make the pull-up R = pull-down R. */ |
| |
| float trans_track_to_cblock_buf; |
| float trans_cblock_to_lblock_buf; |
| |
| max_inputs_to_cblock = 0; |
| |
| /* Assume the two buffers below are 4x minimum drive strength (enough to * |
| * drive a fanout of up to 16 pretty nicely -- should cover a reasonable * |
| * wiring C plus the fanout. */ |
| |
| trans_track_to_cblock_buf = |
| trans_per_buf(R_minW_nmos / 4., R_minW_nmos, R_minW_pmos); |
| |
| trans_cblock_to_lblock_buf = |
| trans_per_buf(R_minW_nmos / 4., R_minW_nmos, R_minW_pmos); |
| |
| num_inputs_to_cblock = (int *)my_calloc(num_rr_nodes, sizeof(int)); |
| maxlen = max(nx, ny) + 1; |
| cblock_counted = (boolean *) my_calloc(maxlen, sizeof(boolean)); |
| |
| ntrans = 0; |
| for(from_node = 0; from_node < num_rr_nodes; from_node++) |
| { |
| |
| from_rr_type = rr_node[from_node].type; |
| |
| switch (from_rr_type) |
| { |
| |
| case CHANX: |
| case CHANY: |
| num_edges = rr_node[from_node].num_edges; |
| cost_index = rr_node[from_node].cost_index; |
| seg_type = rr_indexed_data[cost_index].seg_index; |
| switch_type = segment_inf[seg_type].wire_switch; |
| assert(segment_inf[seg_type].wire_switch == |
| segment_inf[seg_type].opin_switch); |
| assert(switch_inf[switch_type].mux_trans_size >= 1); /* can't be smaller than min sized transistor */ |
| |
| assert(rr_node[from_node].num_opin_drivers == 0); /* undir has no opin or wire switches */ |
| assert(rr_node[from_node].num_wire_drivers == 0); /* undir has no opin or wire switches */ |
| |
| /* Each wire segment begins with a multipexer followed by a driver for unidirectional */ |
| /* Add up area of multiplexer */ |
| ntrans += |
| trans_per_mux(rr_node[from_node].fan_in, |
| trans_sram_bit, |
| switch_inf[switch_type].mux_trans_size); |
| |
| /* Add up area of buffer */ |
| if(switch_inf[switch_type].buf_size == 0) |
| { |
| ntrans += |
| trans_per_buf(switch_inf[switch_type].R, |
| R_minW_nmos, R_minW_pmos); |
| } |
| else |
| { |
| ntrans += switch_inf[switch_type].buf_size; |
| } |
| |
| for(iedge = 0; iedge < num_edges; iedge++) |
| { |
| |
| to_node = rr_node[from_node].edges[iedge]; |
| to_rr_type = rr_node[to_node].type; |
| |
| switch (to_rr_type) |
| { |
| |
| case CHANX: |
| case CHANY: |
| break; |
| |
| case IPIN: |
| num_inputs_to_cblock[to_node]++; |
| max_inputs_to_cblock = |
| max(max_inputs_to_cblock, |
| num_inputs_to_cblock[to_node]); |
| iseg = |
| seg_index_of_cblock(from_rr_type, |
| to_node); |
| |
| if(cblock_counted[iseg] == FALSE) |
| { |
| cblock_counted[iseg] = TRUE; |
| ntrans += |
| trans_track_to_cblock_buf; |
| } |
| break; |
| |
| default: |
| printf |
| ("Error in count_routing_transistors: Unexpected \n" |
| "connection from node %d (type %d) to node %d (type %d).\n", |
| from_node, from_rr_type, to_node, |
| to_rr_type); |
| exit(1); |
| break; |
| |
| } /* End switch on to_rr_type. */ |
| |
| } /* End for each edge. */ |
| |
| /* Reset some flags */ |
| if(from_rr_type == CHANX) |
| { |
| for(i = rr_node[from_node].xlow; |
| i <= rr_node[from_node].xhigh; i++) |
| cblock_counted[i] = FALSE; |
| |
| } |
| else |
| { /* CHANY */ |
| for(j = rr_node[from_node].ylow; |
| j <= rr_node[from_node].yhigh; j++) |
| cblock_counted[j] = FALSE; |
| |
| } |
| break; |
| case OPIN: |
| break; |
| |
| default: |
| break; |
| |
| } /* End switch on from_rr_type */ |
| } /* End for all nodes */ |
| |
| /* Now add in the input connection block transistors. */ |
| |
| input_cblock_trans = get_cblock_trans(num_inputs_to_cblock, |
| max_inputs_to_cblock, |
| trans_cblock_to_lblock_buf, |
| trans_sram_bit); |
| |
| free(cblock_counted); |
| free(num_inputs_to_cblock); |
| |
| ntrans += input_cblock_trans; |
| |
| printf("\nRouting area (in minimum width transistor areas):\n"); |
| printf("Total Routing Area: %#g Per logic tile: %#g\n", ntrans, |
| ntrans / (float)(nx * ny)); |
| } |
| |
| |
| static float |
| get_cblock_trans(int *num_inputs_to_cblock, |
| int max_inputs_to_cblock, |
| float trans_cblock_to_lblock_buf, |
| float trans_sram_bit) |
| { |
| |
| /* Computes the transistors in the input connection block multiplexers and * |
| * the buffers from connection block outputs to the logic block input pins. * |
| * For speed, I precompute the number of transistors in the multiplexers of * |
| * interest. */ |
| |
| float *trans_per_cblock; /* [0..max_inputs_to_cblock] */ |
| float trans_count; |
| int i, num_inputs; |
| |
| trans_per_cblock = (float *)my_malloc((max_inputs_to_cblock + 1) * |
| sizeof(float)); |
| |
| trans_per_cblock[0] = 0.; /* i.e., not an IPIN or no inputs */ |
| |
| /* With one or more inputs, add the mux and output buffer. I add the output * |
| * buffer even when the number of inputs = 1 (i.e. no mux) because I assume * |
| * I need the drivability just for metal capacitance. */ |
| |
| for(i = 1; i <= max_inputs_to_cblock; i++) |
| trans_per_cblock[i] = |
| trans_per_mux(i, trans_sram_bit, |
| ipin_mux_trans_size) + trans_cblock_to_lblock_buf; |
| |
| trans_count = 0.; |
| |
| for(i = 0; i < num_rr_nodes; i++) |
| { |
| num_inputs = num_inputs_to_cblock[i]; |
| trans_count += trans_per_cblock[num_inputs]; |
| } |
| |
| free(trans_per_cblock); |
| return (trans_count); |
| } |
| |
| |
| static float * |
| alloc_and_load_unsharable_switch_trans(int num_switch, |
| float trans_sram_bit, |
| float R_minW_nmos) |
| { |
| |
| /* Loads up an array that says how many transistors are needed to implement * |
| * the unsharable portion of each switch type. The SRAM bit of a switch and * |
| * the pass transistor (forming either the entire switch or the output part * |
| * of a tri-state buffer) are both unsharable. */ |
| |
| float *unsharable_switch_trans, Rpass; |
| int i; |
| |
| unsharable_switch_trans = (float *)my_malloc(num_switch * sizeof(float)); |
| |
| for(i = 0; i < num_switch; i++) |
| { |
| |
| if(switch_inf[i].buffered == FALSE) |
| { |
| Rpass = switch_inf[i].R; |
| } |
| else |
| { /* Buffer. Set Rpass = Rbuf = 1/2 Rtotal. */ |
| Rpass = switch_inf[i].R / 2.; |
| } |
| |
| unsharable_switch_trans[i] = trans_per_R(Rpass, R_minW_nmos) + |
| trans_sram_bit; |
| } |
| |
| return (unsharable_switch_trans); |
| } |
| |
| |
| static float * |
| alloc_and_load_sharable_switch_trans(int num_switch, |
| float trans_sram_bit, |
| float R_minW_nmos, |
| float R_minW_pmos) |
| { |
| |
| /* Loads up an array that says how many transistor are needed to implement * |
| * the sharable portion of each switch type. The SRAM bit of a switch and * |
| * the pass transistor (forming either the entire switch or the output part * |
| * of a tri-state buffer) are both unsharable. Only the buffer part of a * |
| * buffer switch is sharable. */ |
| |
| float *sharable_switch_trans, Rbuf; |
| int i; |
| |
| sharable_switch_trans = (float *)my_malloc(num_switch * sizeof(float)); |
| |
| for(i = 0; i < num_switch; i++) |
| { |
| |
| if(switch_inf[i].buffered == FALSE) |
| { |
| sharable_switch_trans[i] = 0.; |
| } |
| else |
| { /* Buffer. Set Rbuf = Rpass = 1/2 Rtotal. */ |
| Rbuf = switch_inf[i].R / 2.; |
| sharable_switch_trans[i] = |
| trans_per_buf(Rbuf, R_minW_nmos, R_minW_pmos); |
| } |
| } |
| |
| return (sharable_switch_trans); |
| } |
| |
| |
| static float |
| trans_per_buf(float Rbuf, |
| float R_minW_nmos, |
| float R_minW_pmos) |
| { |
| |
| /* Returns the number of minimum width transistor area equivalents needed to * |
| * implement this buffer. Assumes a stage ratio of 4, and equal strength * |
| * pull-up and pull-down paths. */ |
| |
| int num_stage, istage; |
| float trans_count, stage_ratio, Rstage; |
| |
| if(Rbuf > 0.6 * R_minW_nmos || Rbuf <= 0.) |
| { /* Use a single-stage buffer */ |
| trans_count = trans_per_R(Rbuf, R_minW_nmos) + trans_per_R(Rbuf, |
| R_minW_pmos); |
| } |
| else |
| { /* Use a multi-stage buffer */ |
| |
| /* Target stage ratio = 4. 1 minimum width buffer, then num_stage bigger * |
| * ones. */ |
| |
| num_stage = nint(log10(R_minW_nmos / Rbuf) / log10(4.)); |
| num_stage = max(num_stage, 1); |
| stage_ratio = pow(R_minW_nmos / Rbuf, 1. / (float)num_stage); |
| |
| Rstage = R_minW_nmos; |
| trans_count = 0.; |
| |
| for(istage = 0; istage <= num_stage; istage++) |
| { |
| trans_count += |
| trans_per_R(Rstage, R_minW_nmos) + trans_per_R(Rstage, |
| R_minW_pmos); |
| Rstage /= stage_ratio; |
| } |
| } |
| |
| return (trans_count); |
| } |
| |
| |
| static float |
| trans_per_mux(int num_inputs, |
| float trans_sram_bit, |
| float pass_trans_area) |
| { |
| |
| /* Returns the number of transistors needed to build a pass transistor mux. * |
| * DOES NOT include input buffers or any output buffer. * |
| * Attempts to select smart multiplexer size depending on number of inputs * |
| * For multiplexers with inputs 4 or less, one level is used, more has two * |
| * levels. */ |
| float ntrans, sram_trans, pass_trans; |
| int num_second_stage_trans; |
| |
| if(num_inputs <= 1) |
| { |
| return (0); |
| } |
| else if(num_inputs == 2) |
| { |
| pass_trans = 2 * pass_trans_area; |
| sram_trans = 1 * trans_sram_bit; |
| } |
| else if(num_inputs <= 4) |
| { |
| /* One-hot encoding */ |
| pass_trans = num_inputs * pass_trans_area; |
| sram_trans = num_inputs * trans_sram_bit; |
| } |
| else |
| { |
| /* This is a large multiplexer so design it using a two-level multiplexer * |
| * + 0.00001 is to make sure exact square roots two don't get rounded down * |
| * to one lower level. */ |
| num_second_stage_trans = floor(sqrt(num_inputs) + 0.00001); |
| pass_trans = |
| (num_inputs + num_second_stage_trans) * pass_trans_area; |
| sram_trans = |
| (ceil((float)num_inputs / num_second_stage_trans - 0.00001) + |
| num_second_stage_trans) * trans_sram_bit; |
| if(num_second_stage_trans == 2) |
| { |
| /* Can use one-bit instead of a two-bit one-hot encoding for the second stage */ |
| /* Eliminates one sram bit counted earlier */ |
| sram_trans -= 1 * trans_sram_bit; |
| } |
| } |
| |
| ntrans = pass_trans + sram_trans; |
| return (ntrans); |
| } |
| |
| |
| static float |
| trans_per_R(float Rtrans, |
| float R_minW_trans) |
| { |
| |
| /* Returns the number of minimum width transistor area equivalents needed * |
| * to make a transistor with Rtrans, given that the resistance of a minimum * |
| * width transistor of this type is R_minW_trans. */ |
| |
| float trans_area; |
| |
| if(Rtrans <= 0.) /* Assume resistances are nonsense -- use min. width */ |
| return (1.); |
| |
| if(Rtrans >= R_minW_trans) |
| return (1.); |
| |
| /* Area = minimum width area (1) + 0.5 for each additional unit of width. * |
| * The 50% factor takes into account the "overlapping" that occurs in * |
| * horizontally-paralleled transistors, and the need for only one spacing, * |
| * not two (i.e. two min W transistors need two spaces; a 2W transistor * |
| * needs only 1). */ |
| |
| trans_area = 0.5 * R_minW_trans / Rtrans + 0.5; |
| return (trans_area); |
| } |
