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         (i.e. it would be insanely costly to do them by hand)
 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 \frame{\frametitle{Muxer cases to handle (One/Many to One/Many) etc.}
 132
 133  \begin{itemize}
 134    \item One FN outputs to Many Pins: no problem\\
 135              (weird configuration by end-user, but no damage to ASIC)
 136    \item One Pin to Many FN inputs: no problem\\
 137          (weird configuration by end-user, but no damage to ASIC)
 138    \item Many Pins to One FN input: {\bf Priority Mux needed}\\
 139              No priority mux: Pin1 = HI, Pin0 = LO, ASIC is damaged
 140    \item Many FN outputs simultaneously to one Pin: {\bf does not occur}\\
 141              (not desirable and not possible, as part of the pinmux design)
 142    \item Some FNs (I2C\_SDA, SD\_D0..3) are I/O Buses\\
 143              Bi-directional control of the Pin must be handed to the
 144              FN
 145    \item Nice to have: Bus sets pintype, signal strength etc.\\
 146              e.g. selecting SD/MMC doesn't need manual pin-config.\\
 147              \bf{caveat: get that wrong and the ASIC can't be sold}
 148   \end{itemize}
 149 }
 150
 151
 152 \frame{\frametitle{Pin Configuration, input and output}
 153
 154  In/out: {\bf Note: these all require multiplexing }
 155  \begin{itemize}
 156    \item Output-Enable (aka Input disable): switches pad to In or Out
 157    \item Output (actually an input wire controlling pin's level, HI/LO)
 158    \item Input (actually an output wire set based on pin's driven level)
 159  \end{itemize}
 160  Characteristics: {\bf Note: these do not require multiplexing }
 161  \begin{itemize}
 162    \item Output current level: 10mA / 20mA / 30mA / 40mA
 163    \item Input hysteresis: low / middle / high. Stops signal noise
 164    \item Pin characteristics: CMOS Push-Push / Open-Drain
 165    \item Pull-up enable: built-in 10k (50k?) resistor
 166    \item Pull-down enable: built-in 10k (50k?) resistor
 167    \item Muxing and IRQ Edge-detection not part of the I/O pin
 168   \end{itemize}
 169 }
 170
 171
 172 \frame{\frametitle{Standard GPIO 4-way in/out Mux and I/O pad}
 173  \begin{center}
 174   \includegraphics[height=2.5in]{../shakti/m_class/mygpiomux.jpg}\\
 175   {\bf 4-in, 4-out, pullup/down, hysteresis, edge-detection (EINT)}
 176  \end{center}
 177 }
 178
 179 \frame{\frametitle{Pin Configuration, input and output}
 180
 181  \begin{itemize}
 182    \item Standard Mux design {\bf cannot deal with many-to-one inputs}\\
 183              (SiFive IOF source code from Freedom U310 cannot, either)
 184              \vspace{4pt}
 185    \item I/O pad configuration conflated with Muxer conflated with GPIO
 186          conflated with EINT
 187                      \vspace{4pt}
 188    \item Need to separate all of these out
 189                      \vspace{4pt}
 190    \item EINTs to be separate FNs (managed by RISC-V PLIC)
 191                      \vspace{4pt}
 192    \item GPIO In/Out/Direction treated just like any other FN
 193                      \vspace{4pt}
 194    \item Pad configuration separated and given one-to-one Registers
 195  \end{itemize}
 196 }
 197
 198 \frame{\frametitle{Register-to-pad "control" settings}
 199  \begin{center}
 200   \includegraphics[height=2.5in]{reg_gpio_cap_ctrl.jpg}\\
 201   {\bf pullup/down, hysteresis, current, edge-detection}
 202  \end{center}
 203 }
 204
 205
 206 \frame{\frametitle{In/Out muxing, direction control}
 207  \begin{center}
 208   \includegraphics[height=2.5in]{reg_gpio_fn_ctrl.jpg}\\
 209   {\bf Note: function can control I/O direction}
 210  \end{center}
 211 }
 212
 213
 214 \frame{\frametitle{Simplified I/O pad Block Diagram}
 215  \begin{center}
 216   \includegraphics[height=2.5in]{reg_gpio_pinblock.jpg}\\
 217   {\bf 3 wires: IN, OUT, OUTEN (also = !INEN) }
 218  \end{center}
 219 }
 220
 221
 222 \frame{\frametitle{Output (and OUTEN) Wiring. 2 pins, 2 GPIO, 2 Fns}
 223  \begin{center}
 224   \includegraphics[height=2.5in]{reg_gpio_out_wiring.jpg}\\
 225   {\bf Reg0 for Pin0, Reg1 for Pin1, Output and OUTEN same mux }
 226  \end{center}
 227 }
 228
 229
 230 \frame{\frametitle{Input Selection and Priority Muxing}
 231  \begin{center}
 232   \includegraphics[height=0.75in]{reg_gpio_comparator.jpg}\\
 233   {\bf Muxer enables input selection}\\
 234   \vspace{10pt}
 235   \includegraphics[height=1.25in]{reg_gpio_in_prioritymux.jpg}\\
 236   {\bf However multiple inputs must be prioritised }
 237  \end{center}
 238 }
 239
 240
 241 \frame{\frametitle{Input Mux Wiring}
 242  \begin{center}
 243   \includegraphics[height=2.5in]{reg_gpio_in_wiring.jpg}\\
 244   {\bf Pin Mux selection vals NOT same as FN selection vals}
 245  \end{center}
 246 }
 247
 248
 249 \frame{\frametitle{Summary}
 250
 251  \begin{itemize}
 252    \item TODO
 253   \end{itemize}
 254 }
 255
 256
 257 \frame{
 258   \begin{center}
 259     {\Huge The end\vspace{20pt}\\
 260                    Thank you\vspace{20pt}\\
 261                    Questions?\vspace{20pt}
 262         }
 263   \end{center}
 264
 265   \begin{itemize}
 266         \item http://libre-riscv.org/shakti/m\_class/pinmux/
 267   \end{itemize}
 268 }
 269
 270
 271 \end{document}