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1 | 1 | # GF16 vs Literature: DLFloat, bfloat16, fp16 Comparison |
2 | 2 |
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3 | | -**Version:** 2.1 |
| 3 | +**Version:** 2.2 |
4 | 4 | **Date:** 2026-04-01 |
5 | | -**Status:** BENCH-004a + BENCH-004b complete (FPGA synthesis pending) |
| 5 | +**Status:** BENCH-004a + BENCH-004b complete; BENCH-005 FPGA synthesis complete (unit-level fair comparison); BENCH-006 FPGA synthesis complete (MAC-level comparison), P&R optional |
| 6 | + |
| 7 | +## Attribution Notice |
| 8 | + |
| 9 | +**GF16 adopts IBM's DLFloat format.** The 1/6/9 allocation (6-bit exponent, 9-bit mantissa, bias=31) was first proposed by IBM researchers as DLFloat (Agrawal et al., 2019). GF16 is an **integer-backed implementation** of this format using `u16` storage, bypassing 62+ compiler bugs in half-precision floating-point. The novelty of GF16 lies in its **implementation**, not the format specification. |
| 10 | + |
| 11 | +**References:** |
| 12 | +- Agrawal, A. et al. "DLFloat: A 16-b Floating Point Format Designed for Deep Learning Training and Inference." IEEE VLSI Circuits, 2019. |
| 13 | +- Mellempudi, N. et al. "Representation range needs for 16-bit neural network training." arXiv:2103.15940, 2021. |
6 | 14 |
|
7 | 15 | ## 1. Format Specifications |
8 | 16 |
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@@ -99,7 +107,7 @@ From "Representation Range Needs..." (cite): |
99 | 107 | ## 6. Open Questions |
100 | 108 |
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101 | 109 | 1. **Training stability:** Can models be trained directly in GF16 (not just inference)? |
102 | | -2. **Hardware cost:** LUT/DSP utilization on FPGA (Phase 2) |
| 110 | +2. ~~**Hardware cost:** LUT/DSP utilization on FPGA (Phase 2)~~ ✅ **Measured** (BENCH-005) |
103 | 111 | 3. **Why does bf16 catastrophically fail?** Investigate 7-bit mantissa vs trained weight distribution |
104 | 112 | 4. **Why does ternary catastrophically fail?** Investigate 3-bit quantization of trained vs random weights |
105 | 113 |
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@@ -185,3 +193,177 @@ python3 train_mnist_mlp.py |
185 | 193 | --- |
186 | 194 |
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187 | 195 | **Статус:** Phase 1 (BENCH‑004a + BENCH‑004b) — программная часть завершена, FPGA‑синтез ожидается |
| 196 | + |
| 197 | +## 8. FPGA Synthesis Results (BENCH-005 + BENCH-006) |
| 198 | + |
| 199 | +### 8.1 Hardware Target |
| 200 | + |
| 201 | +| Parameter | Value | |
| 202 | +|-----------|-------| |
| 203 | +| Board | QMTECH XC7A100T-FGG676C | |
| 204 | +| LUT | 63,400 | |
| 205 | +| FF | 129,600 | |
| 206 | +| DSP48 | 240 | |
| 207 | +| BRAM36 | 135 | |
| 208 | +| Target Fmax | ≥92 MHz (ternary baseline) | |
| 209 | + |
| 210 | +### 8.2 Synthesis Results (Yosys) |
| 211 | + |
| 212 | +**Note**: Complete P&R (nextpnr-xilinx) and timing analysis pending. Current metrics from synthesis only. |
| 213 | + |
| 214 | +| Module | Total Cells | LUT | FF | DSP | Estimated LC | Status | |
| 215 | +|--------|------------|-----|----|-----|-------------|--------| |
| 216 | +| **GF16 Adder** (`gf16_add_top.v`) | 171 | 118 | 47 | 95 | ✅ Synthesis OK | |
| 217 | +| **GF16 Multiplier** (`gf16_mul_top.v`) | 148 | 94 | 47* | 67 | ✅ Synthesis OK | |
| 218 | + |
| 219 | +*LUT breakdown (adder):* 34 LUT2 + 23 LUT3 + 15 LUT4 + 16 LUT5 + 30 LUT6 = 118 LUTs |
| 220 | +*LUT breakdown (multiplier):* 27 LUT2 + 33 LUT3 + 17 LUT4 + 8 LUT5 + 9 LUT6 = 94 LUTs |
| 221 | + |
| 222 | +### 8.3 Unit-level FPGA Cost (BENCH-005) |
| 223 | + |
| 224 | +| Unit | LUT | FF | DSP | Estimated LC | Status | |
| 225 | +|------|-----|----|-----|-------------|--------| |
| 226 | +| **ternary_add** | 2 | 2 | 0 | 2 | ✅ Measured (Yosys) | |
| 227 | +| **ternary_mul** | 2 | 2 | 0 | 2 | ✅ Measured (Yosys) | |
| 228 | + |
| 229 | +*Note*: These are **single operations**, minimal 2-LUT adders/multipliers. |
| 230 | + |
| 231 | +**Baseline reference**: Full HSLM inference pipeline = 4,267 LUT |
| 232 | + |
| 233 | +### 8.3a GF16 vs Ternary (Single Operations) |
| 234 | + |
| 235 | +| Unit | LUT | FF | DSP | LUT vs Ternary | Status | |
| 236 | +|------|-----|----|-----|---------------|--------| |
| 237 | +| **gf16_add** | 118 | 47 | 0 | **59×** (2.8x) | ✅ Measured (Yosys) | |
| 238 | +| **gf16_mul** | 94 | 47 | 1 | **47×** (2.2x) | ✅ Measured (Yosys) | |
| 239 | + |
| 240 | +*Finding*: GF16 adder uses **59×** LUTs of ternary adder, **47×** FFs |
| 241 | +*Finding*: GF16 multiplier uses **47×** LUTs of ternary multiplier, **47×** FFs, **1 DSP48E1** |
| 242 | + |
| 243 | +### 8.3b System Context |
| 244 | + |
| 245 | +| Metric | GF16 Adder | GF16 Multiplier | Ternary Baseline | Notes | |
| 246 | +|--------|-------------|----------------|---------------|--------| |
| 247 | +| **Arithmetic Type** | Single ops | Single ops | Full pipeline | | |
| 248 | +| **Purpose** | FPGA unit cost | FPGA unit cost | Inference engine | |
| 249 | +| **Expected LUT** | 5–15 | 10–30 | 4,267 | |
| 250 | +| **Measured LUT** | 118 | 94 | 2 | ✅ Fair comparison | |
| 251 | + |
| 252 | +### 8.4 P&R Status |
| 253 | + |
| 254 | +⏳ **BLOCKED**: nextpnr-xilinx not built. Cannot extract Fmax. |
| 255 | + |
| 256 | +To complete BENCH-005: |
| 257 | +1. Build nextpnr-xilinx: `cd fpga/nextpnr-xilinx && cmake .. && make` |
| 258 | +2. Run P&R: `nextpnr-xilinx --chipdb ... --xdc ... --json ... --fasm ...` |
| 259 | +3. Extract Fmax: Parse timing report |
| 260 | +4. Update Section 8.3a with Fmax values |
| 261 | + |
| 262 | +### 8.5 Files Generated (Unit-level Fair Comparison) |
| 263 | + |
| 264 | +- `fpga/openxc7-synth/ternary_add_top.v` — Minimal ternary adder (2 LUT) |
| 265 | +- `fpga/openxc7-synth/ternary_mul_top.v` — Minimal ternary multiplier (2 LUT) |
| 266 | +- `fpga/openxc7-synth/ternary_ops_tb.v` — Testbench for both units |
| 267 | +- `fpga/openxc7-synth/ternary_add_top.json` — Yosys synthesis (2 cells, 2 LC) |
| 268 | +- `fpga/openxc7-synth/ternary_mul_top.json` — Yosys synthesis (2 cells, 2 LC) |
| 269 | + |
| 270 | +### 8.6 Interpretation (Unit-level FPGA Cost) |
| 271 | + |
| 272 | +1. **GF16 implements full floating-point arithmetic** |
| 273 | + - 118 LUT for addition (align exponents + add mantissas + normalize + round) |
| 274 | + - 94 LUT + 1 DSP48E1 for multiplication (9×9 mantissa multiply on DSP slice) |
| 275 | + - This matches the expected cost range for custom floating-point formats (10¹–10² LUT per operator) |
| 276 | + |
| 277 | +2. **Ternary is minimal boolean logic** |
| 278 | + - 2 LUT per operation confirms ternary baseline is essentially pure logic gates |
| 279 | + - No exponent alignment, no normalization, no rounding — just multiplexers over {-1, 0, +1} |
| 280 | + |
| 281 | +3. **The 47–59× overhead is expected** |
| 282 | + - GF16 = normalized floating-point format with full IEEE 754-like pipeline |
| 283 | + - Ternary = 3-state logic with minimal hardware |
| 284 | + - This is the **price of precision**: 9-bit mantissa vs 1 trit |
| 285 | + |
| 286 | +4. **Resource utilization is negligible** |
| 287 | + - Both GF16 units occupy <0.2% of XC7A100T LUT resources |
| 288 | + - Only 1 of 240 DSP blocks used (multiplier only) |
| 289 | + - **Substantial capacity remains for parallel MAC arrays** |
| 290 | + |
| 291 | +1. **Unit-level fair comparison**: |
| 292 | + - Ternary adder: **2 LUT**, 2 FF, 0 DSP (minimal multiplexers over {-1,0,+1}) |
| 293 | + - Ternary multiplier: **2 LUT**, 2 FF, 0 DSP (XNOR + gate logic) |
| 294 | + - GF16 adder: **118 LUT**, 47 FF, 0 DSP (59× ternary adder) |
| 295 | + - GF16 multiplier: **94 LUT**, 47 FF, 1 DSP (47× ternary multiplier) |
| 296 | + |
| 297 | +2. **Expected behavior**: GF16 is a full 16-bit floating-point format |
| 298 | + - Requires: exponent alignment, mantissa addition, normalization, rounding |
| 299 | + - Ternary is trivial by comparison (3 states, no normalization needed) |
| 300 | + |
| 301 | +3. **System context** (NOT comparable): |
| 302 | + - `hslm_full_top` = 4,267 LUT = full inference pipeline (memory + MAC array + control) |
| 303 | + - GF16 units = single operations (not a full inference engine) |
| 304 | + |
| 305 | +4. **Parallel capacity**: |
| 306 | + - Each GF16 adder: 118 LUT → **~537** parallel units on XC7A100T |
| 307 | + - Each GF16 multiplier: 94 LUT → **~674** parallel units on XC7A100T |
| 308 | + |
| 309 | +### 8.7 All Files Generated |
| 310 | + |
| 311 | +**GF16 modules:** |
| 312 | +- `fpga/openxc7-synth/gf16_add_top.v` — GF16 adder with LED (168 LOC) |
| 313 | +- `fpga/openxc7-synth/gf16_mul_top.v` — GF16 multiplier with LED (147 LOC) |
| 314 | +- `fpga/openxc7-synth/gf16_add_tb.v` — Testbench for adder (90 LOC) |
| 315 | +- `fpga/openxc7-synth/gf16_mul_tb.v` — Testbench for multiplier (81 LOC) |
| 316 | +- `fpga/openxc7-synth/gf16_top.xdc` — Pin constraints (CLK U22, LED T23) |
| 317 | +- `fpga/openxc7-synth/gf16_add_top.json` — Yosys synthesis (171 cells, 118 LUT) |
| 318 | +- `fpga/openxc7-synth/gf16_mul_top.json` — Yosys synthesis (148 cells, 94 LUT) |
| 319 | + |
| 320 | +**Ternary modules (for fair comparison):** |
| 321 | +- `fpga/openxc7-synth/ternary_add_top.v` — Minimal ternary adder (2 LUT) |
| 322 | +- `fpga/openxc7-synth/ternary_mul_top.v` — Minimal ternary multiplier (2 LUT) |
| 323 | +- `fpga/openxc7-synth/ternary_ops_tb.v` — Testbench for both |
| 324 | +- `fpga/openxc7-synth/ternary_add_top.json` — Yosys synthesis (2 LUT) |
| 325 | +- `fpga/openxc7-synth/ternary_mul_top.json` — Yosys synthesis (2 LUT) |
| 326 | + |
| 327 | +### 8.8 MAC-level FPGA Cost (BENCH-006) |
| 328 | + |
| 329 | +| Module | Total Cells | LUT | FF | DSP | Estimated LC | Status | |
| 330 | +|--------|------------|-----|----|-----|-------------|--------| |
| 331 | +| **ternary_mac_16** | 71 | 52 | 69 | 0 | 52 | ✅ Synthesis OK | |
| 332 | +| **gf16_mac_16** | 549 | 71 | 266 | **16** | 549 | ✅ Synthesis OK | |
| 333 | + |
| 334 | +**LUT breakdown (gf16_mac_16):** LUT1=3, LUT2=2, LUT3=8, LUT4=21, LUT5=12, LUT6=14 → **71 LUT** |
| 335 | + |
| 336 | +#### 8.8a GF16 vs Ternary (MAC-level, 16-element dot product) |
| 337 | + |
| 338 | +| Module | LUT | FF | DSP | vs Ternary | Status | |
| 339 | +|--------|-----|----|-----|------------|--------| |
| 340 | +| **ternary_mac_16** | 52 | 69 | 0 DSP | 1× baseline | ✅ Measured (Yosys) | |
| 341 | +| **gf16_mac_16** | 71 | 266 | **16× DSP48E1** | **1.37×** LUT | ✅ Measured (Yosys) | |
| 342 | + |
| 343 | +**Key findings:** |
| 344 | +- GF16 MAC-16 uses **1.37× LUT** of ternary MAC-16 (71 vs 52) |
| 345 | +- GF16 MAC-16 requires **16× DSP48E1** blocks (one per element), ternary uses 0 DSP |
| 346 | +- GF16 MAC-16 has **3.86× FF** (266 vs 69) due to input/output registers + pipeline stages |
| 347 | +- **DSP bottleneck**: GF16 limited to ~15 parallel MAC-16 units by DSP (240 / 16 = 15), ternary can fit ~1,219 units |
| 348 | + |
| 349 | +#### 8.8b Parallel Capacity on XC7A100T |
| 350 | + |
| 351 | +| Format | LUT/unit | FF/unit | DSP/unit | Max Parallel | Bottleneck | |
| 352 | +|--------|-----------|----------|----------|--------------|------------| |
| 353 | +| **Ternary MAC-16** | 52 | 69 | 0 | **~1,219** | None (logic only) | |
| 354 | +| **GF16 MAC-16** | 71 | 266 | 16 | **~15** (DSP-limited) | DSP (240 total) | |
| 355 | + |
| 356 | +#### 8.8c Files Generated (MAC-level) |
| 357 | + |
| 358 | +- `fpga/openxc7-synth/ternary_mac_16.v` — Ternary 16-element dot product (104 LOC) |
| 359 | +- `fpga/openxc7-synth/gf16_mac_16.v` — GF16 16-element dot product (144 LOC) |
| 360 | +- `fpga/openxc7-synth/ternary_mac_16.json` — Yosys synthesis (71 cells, 52 LUT) |
| 361 | +- `fpga/openxc7-synth/gf16_mac_16.json` — Yosys synthesis (549 cells, 71 LUT, 16× DSP48E1) |
| 362 | +- `fpga/openxc7-synth/BENCH-006_RESULTS.md` — MAC-level comparison summary |
| 363 | + |
| 364 | +## References |
| 365 | + |
| 366 | +1. **Agrawal, A. et al.** "DLFloat: A 16-b Floating Point Format Designed for Deep Learning Training and Inference." IEEE VLSI Circuits, 2019. — Original DLFloat format specification (1/6/9, bias=31) |
| 367 | +2. **Mellempudi, N. et al.** "Representation range needs for 16-bit neural network training." arXiv:2103.15940, 2021. — Distribution analysis justifying the 1/6/9 allocation |
| 368 | +3. **Micikevicius, P. et al.** "Mixed precision training." arXiv:1710.03740, 2018. — FP16 training accuracy results |
| 369 | +4. **Wang, Y. et al.** "Training deep neural networks with 8-bit floating point." arXiv:1811.01421, 2018. — BF16 training results |
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