[TriEmbed] Fwd: Fw: Friday evening computer problem

Scott Hall scottghall1 at gmail.com
Fri Jun 15 23:40:57 CDT 2018


---------- Forwarded message ----------
From:        Burt Silverman
Date:        06/15/2018 09:53 PM
Subject:        Friday evening computer problem
------------------------------


I am working with a microcomputer, or System On a Chip (SOC), known as the
ESP8266. The part has things like UARTs built in, and has some general
purpose input/output (GPIO) pins. That is similar to microcomputers I have
worked with previously, but in this case, there are not enough pins to have
separate pins for the UARTs, and the various other peripherals, and the
GPIO, so they share pins. Using some configuration registers, you choose
what function is active. If you look at the top row of the table below, you
can see that there are 5 choices for each pin: Function1, Function2,
Function3, Function4, and Function5. An example is receive data for UART0,
U0RXD, in row 6. Function1 is just that, U0RXD, but Function4 is GPIO3.

The Technical Reference Document tells me that the complete list of
peripherals is:  SDIO (Secure Digital Input/Output Interface), 3 instances
of SPI (Serial Peripheral Interface), but one is known as HSPI, I2C, I2S,
UART0 (Universal Asynchronous Receiver Transmitter), UART1, PWM
(Pulse-Width Modulation), IR (Infrared) Remote Control.

In the spreadsheet below, I see SD names, SPI and HSPI names, I2S names, U0
and U1 names, but nowhere do I see any I2C names, nor any PWM names, nor
any IR names. If you take my word that this is not a trick, like MTDI is a
mystery coding for PWM or I2C or IR -- how can it be that there is no I2C
and no PWM pins and no IR pins in the table? How can I program the device
configuration registers for these functions?

By the way, there is something a bit tricky about the names MTDI, MTCK,
MTMS, and MTDO. If you remove the M from the names you are left with TDI,
TCK, TMS, TDO -- the standard JTAG signal names. The documentation does not
discuss the JTAG interface. It is not part of this exercise. Also, if you
see some names repeated, like MTDO_UMTDO_U..., that is just an artifact of
some carelessness from whoever created the table -- nothing to worry about.

Burt
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