Merge branch 'main' into dev

CHANGELOG.md

@@ -33,12 +33,12 @@
 ## Other
 * none
 ## Known bugs
-* none
+* USB in KISS mode has problem with TX frames
 # 1.2.1 (2021-10-13)
 ## New features
 * none
 ## Bug fixes
-* Digi max and rep values could not be entered when only <LF> line ending was used.
+* Digi max and rep values could not be entered when only LF line ending was used.
 ## Other
 * none
 ## Known bugs
@@ -55,4 +55,4 @@ This is the very first open-source VP-Digi release.
 ## Other
 * Code was partially rewritten (especially digipeater, modem and AX.25 layer)
 ## Known bugs
-* none
+* none

README.md

@@ -1,6 +1,15 @@
 # VP-Digi
 VP-Digi is a functional, cheap, easy to assemble and configure STM32-based APRS digipeater controller with built-in KISS modem.
 
+* 1200 Bd Bell 202 modem (VHF APRS standard)
+* R2R or PWM signal generation
+* Analog-digital busy channel detection (data carrier detection)
+* AX.25 coder/decoder designed for APRS frames
+* digipeater: 4 settable n-N aliases, 4 simple aliases, viscous delay (known from aprx) or direct only, black and white list
+* 8 independent beacons
+* KISS mode (can be used as an ordinary modem with UI-View, APRSIS32, XASTIR etc.)
+* USB and 2 UARTs: independent, running in KISS, monitor or configuration mode
+
 ## Description, schematic, instructions
 If you are not interested in source code, this repository is not for you. You can find full project description, schematics, compiled firmware and instructions [on my website](https://sq8l.pzk.pl/index.php/vp-digi-cheap-and-functional-aprs-digipeater-controller-with-kiss-modem/).
 
@@ -11,7 +20,7 @@ The firmware was written using System Workbench for STM32 (SW4STM32) and you sho
 The project was designed to be running on a Blue Pill board (STM32F103C8T6) with 8MHz crystal. The firmware was written using only register operations (with ST headers) and CMSIS libraries. The HAL is there only for USB. The code is (quite) extensively commented where needed, so it shouldn't be very hard to understand.
 
 ### Demodulator
-There are two demodulators (and decoders) running in parallel to provide better efficiency. The signal is sampled at 38400Hz (32 samples per symbol) by DMA. The interrupt is generated after receiving 4 samples and the samples are decimated. Then they are pushed through a preemphasis/deemphasis filter (if enabled) which equalizes tone amplitudes. Filtered samples are multiplied by locally generated mark and space tones (their I and Q parts - cosine and sine). This gives a correlation factor between the input signal and each tone. In the meanwhile an unfiltered symbol is produced to drive the data carrier detection PLL. The difference of correlation factors is the new sample and is pushed through a low pass filter to eliminate noise. Filtered samples are compared to zero and the demodulated symbol is sent to bit recovery mechanism.
+There are two demodulators (and decoders) running in parallel to provide better efficiency. The signal is sampled at 38400Hz (32 samples per symbol) by DMA. The interrupt is generated after receiving 4 samples and the samples are decimated. Then they are passed through a preemphasis/deemphasis filter (if enabled) which equalizes tone amplitudes. Filtered samples are multiplied by locally generated mark and space tones (their I and Q parts - cosine and sine). This gives a correlation factor between the input signal and each tone. In the meanwhile an unfiltered symbol is produced to drive the data carrier detection PLL. The difference of correlation factors is the new sample and is passed through a low pass filter to eliminate noise. Filtered samples are compared to zero and the demodulated symbol is sent to bit recovery mechanism.
 ### Bit recovery (and NRZI decoder)
 Bit recovery mechanism is based on a digital PLL. The PLL is nominally running at 1200Hz (=1200 Baud). The symbol change should occur near PLL counter zero, so that the counter overflows in the middle of the symbol and the symbol value is sampled. With every symbol change the counter is multiplied by a <1 factor to bring it closer to zero, keeping the PLL and incoming signal in phase. The DCD signal is multiplexed from both modems. Explained more in [modem.c](Src/drivers/modem.c). Sampled symbol is decoded by NRZI decoder and sent to AX.25 layer.
 ### AX.25 decoding
@@ -23,9 +32,9 @@ AX.25 encoder is also quite simple. It can handle multiple frames in a row (limi
 ### Modulator (and NRZI encoder)
 The NRZI encoder runs at exactly 1200Hz (=1200 Baud) and requests bits from the AX.25 encoder. Bits are encoded to symbols and the DAC sampling timer interval is set depending on symbol value. Because of that there is only one sine table used. For 1200Hz tone the timer interval is larger than for 2200 Hz tone - the sampling frequency is changed to change the output signal frequency. An array index is always kept so that the output signal phase is continuous.
 ## Using VP-Digi code in your project
-I would love to hear about projects which implement VP-Digi source code. If you are making one, let me know at sq8vps<at>gmail.com.
+I would love to hear about projects which implement VP-Digi source code. If you are making one, let me know at sq8vps(at)gmail.com.
 ## References
-The project took a lot of time, but now it's probably the most effective, publicly available, STM32-based modem and the most customizable microcontroller-based APRS digipeater. I would like to mention some resources I found really useful or inspiring:
+The project took a lot of time to finish, but now it's probably the most effective, publicly available, STM32-based modem and the most customizable microcontroller-based APRS digipeater. I would like to mention some resources I found really useful or inspiring:
 * [multimon-ng](https://github.com/EliasOenal/multimon-ng) - general demodulator idea (correlation)
 * [BeRTOS](https://github.com/develersrl/bertos) - AX.25 decoder
 * [Forum thread by SP8EBC](http://forum.aprs.pl/index.php?topic=2086.0) - inspiration
@@ -36,4 +45,4 @@ The project took a lot of time, but now it's probably the most effective, public
 All contributions are appreciated, but please keep the code reasonably clean. Also, please make sure that the firmware is working well before creating a pull request.
 
 ## License
-The project is licensed under the GNU GPL v3 license (see [LICENSE](LICENSE)).
+The project is licensed under the GNU GPL v3 license (see [LICENSE](LICENSE)).