"Come on, come on, turn the radio on
It's Friday night, and it won't be long
Gotta do my hair, put my make-up on
It's Friday night, and it won't be long
'Til I hit the dance floor, hit the dance floor
I got all I need
No, I ain't got cash, I ain't got cash
But I got you, baby
Baby, I don't need dollar bills to have fun tonight
(I love cheap thrills)" - Sia, Cheap Thrills
Firmware Over The Air programming (OTA) is all the rage with Internet of Things (IoT) devices. Ongoing privacy and security issues make it almost mandatory that they be upgradeable after installation. That usually means OTA upgrades using a smartphone App or a desktop browser.
For a hobbyist, or just plain fast and cheap development, few systems beat the ESP8266-based IoT OTA, ArduinoOTA. The ESP8266 has a few flaws. It is difficult to operate on small batteries: sleep mode still requires milliamps and while using WiFi it can surge to 100mA. Also, executing the WiFi stack takes priority and this sometimes causes interrupt service routines to have unpredictable delays. Most applications are OK with this, unless your code is time-critical like trying to a dimmer triac while connected to WiFi.
Microchip CPUs in particular shine at low-cost, low-power performance and raw horsepower. But their WiFi OTA solutions tend towards the later, more expensive models. Wouldn't it be great if we can have OTA for the Microchip CPU, say a PIC16F84 or even a PIC16F1705 if you want to roll C code? In particular the latter has a mouth-watering dedicated zero-crossing detect (ZCD) interrupt which would be very handy for a flicker-free dimmer or a heavy-duty switching of inductive loads.
It turns out this can be done. We build an ESP8266 into a Microchip PIC system and use the former's WiFi capability to program the PIC. WithArduinoOTA, both the ESP8266 and PIC have OTA. Microchip's recommendation is to use a bootloader, ie reserve dedicated program space in the PIC for bootloader so that it can be programmed via its serial port. This possible for the PIC161705 but would would be a very tight squeeze for the PIC16F84 - the low-end PICs are usually short on memory. In addition the bootloader would be unable to change certain startup configuration bits.
 |
| PICkit 2 programmer (left) connected to a target system via its JTAG port |
There is another way to do serial programming for a Microchip PIC: most of them support In-Circuit Serial Programming or ICSP. This is the same method a Microchip Programmer like the PICkit 2 uses. An ESP8266 program speaking ICSP to the PIC will be able to program it without resorting to a bootloader. It turns out this has already been done: mengstr's esppic hackaday project. His source code is in github.
This post really has little to add to mengstr's work, except maybe a little documentation on how to get it up and running, and with luck add some support for the PIC16F84 or even the venerable PIC16F57.
 |
| Schematic for target CPU board |
The ESP-12E to JTAG programming connector pinout is:
Pickit2 ESP-12E
Pin 1 MCLR/Vpp D0/GPIO16
Pin 2 Vdd 3V3
Pin 3 Gnd Gnd
Pin 4 Dat D1/GPIO5
Pin 5 Clk D2/GPIO4
Pin 6 N/C
This way the PIC16F1705 development board can be programmed from both the PICkit 2 and the ESP-12E. The JTAG port also lets you run the target system directly from the PICkit 2. Not having to unplug the target system and hooking it up to another power source greatly speeds up the development cycle.
PICkit 2 might need an updated
PK2DeviceFile.dat file for the PIC16F1705. In my case I use pk2cmd with Linux. pk2cmd needs to be updated to work with Gerhard Bertelsmann's version of pk2cmd. It is tucked away in a gigantic 300MB misc repository, so I copied it
here for your convenience. To compile, simply:
$make linux
To test, plug the target CPU board into the PICkit 2 JTAG port.
$./pk2cmd -PPIC16F1705 -GC
Read successfully.
Configuration Memory
3EFF 3F87
Operation Succeeded
To program,
$./pk2cmd -PPIC16F1705 -Fblink_led.hex -M
PICkit 2 Program Report
18-5-2021, 9:38:13
Device Type: PIC16F1705
Program Succeeded.
Operation Succeeded
To run,
$./pk2cmd -PPIC16F1705 -GC -T -R
To stop running (in order to unplug)
$./pk2cmd -PPIC16F1705 -GC
To compile my program I used sdcc sample code from
Diego Herranz. For Debian sdcc installation is simply:
#apt-get update
#apt-get sdcc
For Slackware it is a little bit more involved. We need the pic14-port ad pic16-port so first get the
gputils source code.
$make clean
$su -c "make install"
Next, untar it:
$tar -xvjf sdcc-src-3.9.0.tar.bz2
Then build it:
$./configure
$su -c "make install"
Here is Diego Herranz's pic14/1.blink_led/blink_led.c modified slightly for the PIC16F1705:
// Copyright (C) 2014 Diego Herranz
#define NO_BIT_DEFINES
#include <pic14regs.h>
#include <stdint.h>
// Oscillator Selection bits (INTOSCIO oscillator: I/O function on RA6/OSC2/CLKOUT pin, I/O function on RA7/OSC1/CLKIN),
// disable watchdog,
// and disable low voltage programming.
// The rest of fuses are left as default.
//__code uint16_t __at (_CONFIG1) __configword = _INTRC_OSC_NOCLKOUT & _WDTE_OFF & _LVP_OFF;
__code uint16_t __at (_CONFIG1) __configword = _FOSC_INTOSC & _WDTE_OFF & _LVP_OFF;
#define LED_PORT PORTCbits.RC0
#define LED_TRIS TRISCbits.TRISC0
// Uncalibrated delay, just waits a number of for-loop iterations
void delay(uint16_t iterations)
{
uint16_t i;
for (i = 0; i < iterations; i++) {
// Prevent this loop from being optimized away.
__asm nop __endasm;
}
}
void main(void)
{
LED_TRIS = 0; // Pin as output
LED_PORT = 0; // LED off
while (1) {
LED_PORT = 1; // LED On
//delay(30000); // ~500ms @ 4MHz
delay(5000); // ~500ms @ 4MHz
LED_PORT = 0; // LED Off
//delay(30000); // ~500ms @ 4MHz
delay(5000); // ~500ms @ 4MHz
}
}
To compile it:
$sdcc -mpic14 -p16f1705 --use-non-free blink_led.c
If you do not want the hassle of compiling it, here is the hex file:
:020000040000FA
:10000000000080310328DE30FB008030FC008030AF
:100010008031832080312C00A1007C08A000E030DA
:10002000A2008030A3002C002008A4002108A50015
:10003000FF30A007031CA10324082504031980280E
:1000400004302207A400A501A50D2308A507240854
:10005000FB002508FC0080308031832080312C009B
:10006000A7007C08A6002208FB002308FC008030C3
:100070008031832080312C00A900A5007C08A800D5
:10008000A40002302207A400A501A50D2308A5079E
:100090002408FB002508FC0080308031832080315B
:1000A0002C00A500AB007C08A400AA002C002608A8
:1000B000AA002708AB00FF30A607031CA7032A08E5
:1000C0002B0403197A282808FB002908FC0080303B
:1000D0008031A02080312C00AA002408840025084B
:1000E00085002A088000A80A0319A90AA40A03198E
:1000F000A50A562806302C00A2070318A30A1328C5
:100100008031B2280800003A03198B28803A03197D
:100110009328FC0100347B0884007C0885001200D1
:10012000FC00000808008031AD20FA00FB0FFC0342
:10013000FC0A8031AD20F9007A08FC00790808003B
:10014000003A0319A728803A0319AD2800347B0828
:1001500084007C088500000808007C088A007B0871
:100160008200080021000E1020000E1020000E1446
:100170008830FC0013308031C820803120000E1000
:100180008830FC0013308031C8208031B628080048
:100190002C00AD007C08AC00AE01AF012C002D0896
:1001A0002F02031D02322C082E020318DD28000046
:1001B0002C00AE0A0319AF0ACE280800013400341F
:0E01C000E634003430340634013400340034A8
:020000040001F9
:02000E00E41FED
:00000001FF
Next we move on to the Arduino IDE to compile
mengstr's esppic code over at
his github repository. The ESP8266 code is in https://github.com/mengstr/esppic/tree/master/esppic, and you need to set the compile settings for NodeMCU ESP-12E, CPU speed 80MHz.
You will also probably need to pull in a library from
Websockets library from here. In addition you will need to put in the same local Arduino code directory, a sub-directory named
data and fill it with the files from mengstr's https://github.com/mengstr/esppic/tree/master/assets. They are necessary for the webserver code for the ESP8266.
In the Arduino IDE, go to Tools->ESP8266 Data Upload and program the SPIFFS data/ files. Next, program the ESP8266 NodeMCU via the USB port. It comes up as a WiFi Access Point, so connect to it, maybe with your smartphone or laptop. With a browser, connect to http://192.168.4.1 and type in your WiFi SSID and password.
 |
| NodeMCU ESP-12E wired to JTAG port of PIC16F1705 target CPU board |
Now power off and connect it to the JTAG port of the PIC16F1705 target board. Make sure in Arduino IDE you have the Debug Monitor active at the USB serial port, as it will come up with the IP address as it starts up. Say it is 12.34.56.78. With a browser, connect to http://12.34.56.78.
You should see something like this in the Debug Monitor :
Connecting to wifi using default info
..
Successfully connected. IP=12.34.56.78
handleFileRead(/)
/index.html (0 bytes) Open:53 Stream:1 Close:0
handleFileRead(/)
 |
| Screenshot of programming webpage |
You should first try reading the CONFIG1 and CONFIG2 registers. In my case I had trouble getting a brand-new blank PIC16F1705 to work; I had to first program it with the PICkit 2. If it works, the browser should show:
MEMORY DUMP
DEV ID : 3055
DEV REV: 2003
CONFIG1: 1fe4 (0001 1111 1110 0100)
CONFIG2: 3fff (0011 1111 1111 1111)
USER ID: 3fff 3fff 3fff 3fff
Followed by a memory dump, something like:
0000: 0000 3180 2803 30DE 00FB 3080 00FC 3080 3180 2083 3180 002C 00A1 087C 00A0 30E0
0010: 00A2 3080 00A3 002C 0820 00A4 0821 00A5 30FF 07A0 1C03 03A1 0824 0425 1903 2880
0020: 3004 0722 00A4 01A5 0DA5 0823 07A5 0824 00FB 0825 00FC 3080 3180 2083 3180 002C
...
To program use a browser, or navigator or Konqueror to drag the hex file over to the programming icon. I could not get mine to work with Google Chrome, but Konqueror or Firefox works for me.
Sometimes esppic locks up during a memory dump or programming; I find it best to simply power-cycle it and start afresh. For some reason I could not get it to recover from an error condition. Notice the PIC16F1705's programming datasheet recommends using 5V while programming and we are using 3.3V so maybe this caused the flakiness. You can at a pinch wire it to the ESP-12E's 5V, but I would not recommend long-term usage like that as the ESP8266 datasheet says it is a 3.3V device and mught get over-stressed. It would be instructive to try the PIC16LF1705, which is an explicitly low-voltage version.
There you have it, WiFi OTA for the Microchip PIC16F1705. I don't need dollar bills to have fun tonight. I love cheap thrills.
Happy Trails.
Support for 18f56k42 ?thanks!
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