Fixed push-push to push-pull

[libreriscv.git] / shakti / m_class / pinmux.mdwn

diff --git a/shakti/m_class/pinmux.mdwn b/shakti/m_class/pinmux.mdwn
index 2243e40b398b8a554d5d22222f752be8e44acfe1..9ef3c5f8f3ac1fa7004a10cf0ab04e006ffaa9ca 100644 (file)
--- a/shakti/m_class/pinmux.mdwn
+++ b/shakti/m_class/pinmux.mdwn
@@ -6,8 +6,9 @@
   is a Watchdog Timer and others.
 * <https://github.com/sifive/freedom/blob/master/src/main/scala/everywhere/e300artydevkit/Platform.scala>
   Pinmux ("IOF") for multiplexing several I/O functions onto a single pin
+* <https://bitbucket.org/casl/pinmux.git> - implementation by Shakti RISE Group
 
-Complex!  
+Surprisingly complex!  
 
 # Requirements
 
@@ -18,16 +19,38 @@ optional pull-up and pull-down resistors, in an IDENTICAL fashion to
 that of ALL major well-known embedded SoCs from ST Micro, Cypress,
 Texas Instruments, NXP, Rockchip, Allwinner and many many others".
 
+* The IO pad shall have pull-up enable, pull-down enable, variable
+  frequency de-bounce (schmidt trigger), tri-state capability, 
+  variable current drive (on input), Open Drain and CMOS Push-Push.
+* Certain functions shall have the ability to control whether
+  IO pads will be input or output (not the GPIO registers).
+* Number of wires shall be minimised especially in cases where
+  the IO pad (puen, oe) need to change under the control of the
+  function (not the GPIO registers).
+* The amount of latency (gates in between I/O pad and function)
+  shall be minimised
+* There shall be no short-circuits created by multiple input
+  pins trying to drive the same input function
+* There shall be no short-circuits even when functions control
+  when the IO pad is an input.
+
 ## Analysis
 
 Questions:
 
-* Can damage occur by outputs being short-circuited to outputs in any way?
+* Can damage occur (to the ASIC) by outputs being short-circuited to outputs
+  in any way?
   A partial analysis showed that because outputs are one-to-many, there should
   not be a possibility for that to occur.  However what if a function is
   bi-directional?
 * Is de-bouncing always needed on every input?  Is it ok for de-bouncing
   to be only done on EINT?
+* Can the input mux be turned round and "selector" logic added so that
+  there is no possibility of damage to inputs?
+
+# Images
+
+* [[mygpiomux.jpg]]
 
 # GSoC2018
 
@@ -39,12 +62,31 @@ Introductions:
   lots of different stuff.  Guardian of the EOMA68 Certification Mark,
   and currently responsible for coordinating the design of a fully Libre
   RISC-V SoC in collaboration with the RISE Group, IIT Madras, Shakti Project.
+  not much experience at verilog (have done a couple of tutorials).
+* Aurojyoti Das(auro) - graduate student (MSc Electrical - Microelectronics) 
+  at TU Delft, Netherlands. C/C++, Verilog, VHDL, SystemVerilog, RTL Design, 
+  Logic Verification, Python/Perl/Shell scripting, Analog IC Design (currently learning) 
+  
+Hardware available:
+
+* lkcl: ZC706
+* xing: zynq-7020 and Xilinx XC7A100T-484 if needed contact him! <higuoxing@gmail.com>
 
 # Discussion and Links
 
+* <https://elinux.org/images/b/b6/Pin_Control_Subsystem_Overview.pdf>
 * <https://lists.librecores.org/pipermail/discussion/2018-February/thread.html>
 * <https://lists.librecores.org/pipermail/discussion/2018-January/000404.html>
 
+# Some Useful Resource
+* <https://github.com/ucb-bar/generator-bootcamp> Interactive tutorial on Scala and Chisel (best one, take it, trust me!)
+* <https://docs.scala-lang.org/tour/tour-of-scala.html> A brief Scala tutorial
+* <https://github.com/ucb-bar/chisel-tutorial> A brief Chisel tutorial
+* <https://github.com/xfguo/tbgen/blob/master/tbgen.py> auto-generated test module for verilog
+* <https://github.com/kdurant/verilog-testbench> described here <https://www.vim.org/scripts/script.php?script_id=4596>
+* <http://agilesoc.com/open-source-projects/svunit/> - SVunit - unit testing for verilog
+* [FPGA Overview](http://www.springer.com/cda/content/document/cda_downloaddocument/9781461435938-c2.pdf?SGWID=0-0-45-1333135-p174308376) Useful in writing GPIO related codes...
+
 # Pinouts Specification
 
 Covered in [[pinouts]].  The general idea is to target several
@@ -92,14 +134,14 @@ Relying on this capability, however, by selecting a fixed voltage for
 the entire SoC's GPIO domain, is simply not a good idea: all sensors
 and peripherals which do not have a variable (VREF) capability for the
 logic side, or coincidentally are not at the exact same fixed voltage,
-will simply not be compatible if they are high-speed CMOS-level push-push
+will simply not be compatible if they are high-speed CMOS-level push-pull
 driven.  Open-Drain on the other hand can be handled with a MOSFET for
 two-way or even a diode for one-way depending on the levels, but this means
 significant numbers of external components if the number of lines is large.
 
 So, selecting a fixed voltage (such as 1.8v or 3.3v) results in a bit of a
 problem: external level-shifting is required on pretty much absolutely every
-single pin, particularly the high-speed (CMOS) push-push I/O.  An example: the
+single pin, particularly the high-speed (CMOS) push-pull I/O.  An example: the
 DM9000 is best run at 3.3v.  A fixed 1.8v FlexBus would
 require a whopping 18 pins (possibly even 24 for a 16-bit-wide bus)
 worth of level-shifting, which is not just costly