pinmux/pinmux_chennai_2018.tex

   1 \documentclass[slidestop]{beamer}
   2 \usepackage{beamerthemesplit}
   3 \usepackage{graphics}
   4 \usepackage{pstricks}
   5
   6 \title{Pin Multiplexer}
   7 \author{Rishabh Jain}
   8 \author{Luke Kenneth Casson Leighton}
   9
  10
  11 \begin{document}
  12
  13 \frame{
  14    \begin{center}
  15     \huge{Pin Multiplexer}\\
  16     \vspace{32pt}
  17     \Large{Auto-generating documentation, code \\
  18                         and resources for a Pinmux}\\
  19     \vspace{24pt}
  20     \Large{[proposed for] Chennai 9th RISC-V Workshop}\\
  21     \vspace{16pt}
  22     \large{\today}
  23   \end{center}
  24 }
  25
  26
  27 \frame{\frametitle{Credits and Acknowledgements}
  28
  29  \begin{itemize}
  30    \item TODO\vspace{10pt}
  31   \end{itemize}
  32 }
  33
  34
  35 \frame{\frametitle{Glossary}
  36
  37  \begin{itemize}
  38    \item GPIO: general-purpose reconfigureable I/O (Input/Output).
  39    \item Pin: an I/O pad.  May be driven (input) or may drive (output).
  40    \item FN: term for a single-wire "function", such as UART\_TX,
  41              I2C\_SDA, SDMMC\_D0 etc.  may be an input, output or both
  42                  (bi-directional case: two wires are always allocated, one
  43                   for input to the function and one for output from the function).
  44    \item Bus: a group of bi-directional functions (SDMMC D0 to D3)
  45          where the direction is ganged and under the Bus's control
  46    \item Input Priority Muxer: a multiplexer with N selector
  47                  wires and N associated inputs.  The lowest (highest?) indexed
  48                  "selector" enabled results in its
  49                  input being routed to the output.
  50    \item Output Demuxer: a one-to-many "redirector" where a single
  51              input is "routed" to any one output, based
  52              on a selector.
  53   \end{itemize}
  54 }
  55
  56
  57 \frame{\frametitle{Why, How and What is a Pinmux?}
  58
  59  \begin{itemize}
  60    \item Why? To save cost, increase yield, and to target multiple
  61          markets with the same design, thereby increasing uptake
  62          and consequently taking advantage of volume pricing.\vspace{4pt}
  63          \\
  64          Summary: it's all about making more money!\vspace{4pt}
  65    \item How? By multiplexing many more functions (100 to 1,200) than there
  66          are actual available pins (48 to 500), the required chip package
  67              is far less costly and the chip more desirable\vspace{4pt}
  68    \item What? A many-to-many dynamically-configureable router of
  69          I/O functions to I/O pins\vspace{4pt}
  70    \item \bf{Note: actual muxing is deceptively simple, but like
  71          a DRAM cell it's actually about the ancillaries / extras}
  72   \end{itemize}
  73 }
  74
  75
  76 \frame{\frametitle{Associated Extras}
  77
  78  \begin{itemize}
  79    \item Design Specification
  80    \item Scenario analysis (whether the chip will fit "markets")
  81    \item Documentation: Summary sheet, Technical Reference Manual.
  82    \item Test suites
  83    \item Control Interface (AXI4 / Wishbone / TileLink / other)
  84    \item Simulation
  85    \item Linux kernel drivers, DTB, libopencm3, Arduino libraries etc.
  86   \end{itemize}
  87  Example context:
  88  \begin{itemize}
  89    \item Shakti M-Class has 160 pins with a 99.5\% full 4-way mux
  90    \item Almost 640-way routing, 6 "scenarios" (7th TBD),
  91          100+ page Manual needed,
  92          \bf{17,500 lines of auto-generated code}
  93   \end{itemize}
  94 }
  95
  96
  97 \frame{
  98   \vspace{30pt}
  99   \begin{center}
 100     {\Huge
 101                    ALL of these\vspace{20pt}\\
 102                    can be\vspace{20pt}\\
 103                    auto-generated\vspace{30pt}
 104         }
 105         \\
 106         (from the Design Specification, after Scenario Analysis)
 107   \end{center}
 108
 109 }
 110
 111 \frame{\frametitle{Reduce workload, reduce duplication, reduce risk and cost}
 112
 113  \begin{itemize}
 114    \item Auto-generate everything: documentation, code, libraries etc.
 115              \vspace{10pt}
 116    \item Standardise: similar to PLIC, propose GPIO and Pinmux
 117              \vspace{10pt}
 118    \item Standardise format of configuration registers:
 119              saves code duplication effort (multiple software environments)
 120                  \vspace{10pt}
 121    \item Add support for multiple code formats: Chisel3 (SiFive IOF),
 122              BSV (Bluespec), Verilog, VHDL, MyHDL.
 123                  \vspace{10pt}
 124    \item Multiple auto-generated code-formats permits cross-validation:\\
 125              auto-generated test suite in one HDL can validate a muxer
 126              generated for a different target HDL.
 127                  \vspace{10pt}
 128   \end{itemize}
 129 }
 130
 131
 132 \frame{\frametitle{Design Spec and Scenario Analysis}
 133
 134  \begin{itemize}
 135    \item Analyse the target markets that the chip will sell in\\
 136              (multiple markets increases sales volume, reduces chip cost)
 137              \vspace{4pt}
 138    \item Create a formal (python-based) specification for the pinmux
 139              \vspace{4pt}
 140    \item Add scenarios then check that they meet the requirements\\
 141              { \bf (before spending money on hardware engineers!) }
 142              \vspace{4pt}
 143    \item Scenarios represent target markets: ICs to be connected\\
 144          (GPS, NAND IC, WIFI etc.  May require draft schematics
 145          drawn up, or client-supplied schematics analysed).
 146                  \vspace{4pt}
 147    \item Analyse the scenarios: if pins are missing, alter and repeat.\\
 148                  \vspace{4pt}
 149    \item Eventually the pinmux meets all requirements...\\
 150              { \bf without spending USD \$5-50m to find out it doesn't!}
 151   \end{itemize}
 152 }
 153
 154
 155 \frame{\frametitle{Why Standardise (like PLIC in priv-spec)?}
 156
 157  \begin{itemize}
 158    \item TODO - huge cost savings in hardware and software.
 159   \end{itemize}
 160 }
 161
 162
 163 \frame{\frametitle{Muxer cases to handle (One/Many to One/Many) etc.}
 164
 165  \begin{itemize}
 166    \item One FN outputs to Many Pins: no problem\\
 167              (weird configuration by end-user, but no damage to ASIC)
 168    \item One Pin to Many FN inputs: no problem\\
 169          (weird configuration by end-user, but no damage to ASIC)
 170    \item Many Pins to One FN input: {\bf Priority Mux needed}\\
 171              No priority mux: Pin1 = HI, Pin0 = LO, ASIC is damaged
 172    \item Many FN outputs simultaneously to one Pin: {\bf does not occur}\\
 173              (not desirable and not possible, as part of the pinmux design)
 174    \item Some FNs (I2C\_SDA, SD\_D0..3) are I/O Buses\\
 175              Bi-directional control of the Pin must be handed to the
 176              FN
 177    \item Nice to have: Bus sets pintype, signal strength etc.\\
 178              e.g. selecting SD/MMC doesn't need manual pin-config.\\
 179              \bf{caveat: get that wrong and the ASIC can't be sold}
 180   \end{itemize}
 181 }
 182
 183
 184 \frame{\frametitle{Pin Configuration, input and output}
 185
 186  In/out: {\bf Note: these all require multiplexing }
 187  \begin{itemize}
 188    \item Output-Enable (aka Input disable): switches pad to In or Out
 189    \item Output (actually an input wire controlling pin's level, HI/LO)
 190    \item Input (actually an output wire set based on pin's driven level)
 191  \end{itemize}
 192  Characteristics: {\bf Note: these do not require multiplexing }
 193  \begin{itemize}
 194    \item Output current level: 10mA / 20mA / 30mA / 40mA
 195    \item Input hysteresis: low / middle / high. Stops signal noise
 196    \item Pin characteristics: CMOS Push-Push / Open-Drain
 197    \item Pull-up enable: built-in 10k (50k?) resistor
 198    \item Pull-down enable: built-in 10k (50k?) resistor
 199    \item Muxing and IRQ Edge-detection not part of the I/O pin
 200   \end{itemize}
 201 }
 202
 203
 204 \frame{\frametitle{Standard GPIO 4-way in/out Mux and I/O pad}
 205  \begin{center}
 206   \includegraphics[height=2.5in]{../shakti/m_class/mygpiomux.jpg}\\
 207   {\bf 4-in, 4-out, pullup/down, hysteresis, edge-detection (EINT)}
 208  \end{center}
 209 }
 210
 211 \frame{\frametitle{Separating Pin Configuration, input and output}
 212
 213  \begin{itemize}
 214    \item Standard Mux design {\bf cannot deal with many-to-one inputs}\\
 215              (SiFive IOF source code from Freedom U310 cannot, either)
 216              \vspace{4pt}
 217    \item I/O pad configuration conflated with In-Muxer conflated with
 218                  Out-Muxer conflated with GPIO conflated with EINT.
 219                      \vspace{4pt}
 220  \end{itemize}
 221    {\bf IMPORTANT to separate all of these out:
 222                      \vspace{4pt}}
 223  \begin{itemize}
 224    \item EINTs to be totally separate FNs. managed by RISC-V PLIC\\
 225          (If every GPIO was an EINT it would mean 100+ IRQs)
 226                      \vspace{4pt}
 227    \item GPIO In/Out/Direction treated just like any other FN\\
 228              (but happen to have AXI4 - or other - memory-mapping)
 229                      \vspace{4pt}
 230    \item Pad configuration separated and given one-to-one Registers\\
 231              (SRAMs set by AXI4 to control mux, pullup, current etc.)
 232  \end{itemize}
 233 }
 234
 235 \frame{\frametitle{Register-to-pad "control" settings}
 236  \begin{center}
 237   \includegraphics[height=2.5in]{reg_gpio_cap_ctrl.jpg}\\
 238   {\bf pullup/down, hysteresis, current, edge-detection}
 239  \end{center}
 240 }
 241
 242
 243 \frame{\frametitle{In/Out muxing, direction control: GPIO just a FN}
 244  \begin{center}
 245   \includegraphics[height=2.5in]{reg_gpio_fn_ctrl.jpg}\\
 246   {\bf Note: function can control I/O direction}
 247  \end{center}
 248 }
 249
 250
 251 \frame{\frametitle{GPIO (only): Simplified I/O pad Diagram (FN only)}
 252  \begin{center}
 253   \includegraphics[height=2.5in]{reg_gpio_pinblock.jpg}\\
 254   {\bf 3 wires: IN, OUT, OUTEN (also = !INEN) }
 255  \end{center}
 256 }
 257
 258
 259 \frame{\frametitle{Output (and OUTEN) Wiring. 2 pins, 2 GPIO, 2 Fns}
 260  \begin{center}
 261   \includegraphics[height=2.5in]{reg_gpio_out_wiring.jpg}\\
 262   {\bf Reg0 for Pin0, Reg1 for Pin1, Output and OUTEN same mux }
 263  \end{center}
 264 }
 265
 266
 267 \frame{\frametitle{Input Selection and Priority Muxing}
 268  \begin{center}
 269   \includegraphics[height=0.75in]{reg_gpio_comparator.jpg}\\
 270   {\bf Muxer enables input selection}\\
 271   \vspace{10pt}
 272   \includegraphics[height=1.25in]{reg_gpio_in_prioritymux.jpg}\\
 273   {\bf However multiple inputs must be prioritised }
 274  \end{center}
 275 }
 276
 277
 278 \frame{\frametitle{Input Mux Wiring}
 279  \begin{center}
 280   \includegraphics[height=2.5in]{reg_gpio_in_wiring.jpg}\\
 281   {\bf Pin Mux selection vals NOT same as FN selection vals}
 282  \end{center}
 283 }
 284
 285
 286 \frame{\frametitle{Summary}
 287
 288  \begin{itemize}
 289    \item TODO
 290   \end{itemize}
 291 }
 292
 293
 294 \frame{
 295   \begin{center}
 296     {\Huge The end\vspace{20pt}\\
 297                    Thank you\vspace{20pt}\\
 298                    Questions?\vspace{20pt}
 299         }
 300   \end{center}
 301
 302   \begin{itemize}
 303         \item http://libre-riscv.org/shakti/m\_class/pinmux/
 304   \end{itemize}
 305 }
 306
 307
 308 \end{document}