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#uart

1 post1 participant0 posts today
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Johannes Kastl

Dear #homelab bubble,

as is normal I have a dozen different SBCs (Raspi1, Raspi2, Raspi4,...) as well as some other thin clients running in my home lab. As none of them is connected to a monitor, each of them has some kind of serial-to-USB cable attached (to a serial output or to the Raspi GPIO pins).

Of course, I am lazy, and moving the laptop I am working on and attaching the right cable is too much effort. So I thought about finding another solution. Not sure if there is one and if I can afford it. So I would be glad if there is any input or ideas or hints or experiences or recommendations. Thanks in advance!

#serialconsole#uart#raspi
Public
e_es

Nach #Weihnachten habe ich MacroPads (kleine USB-Tastaturen mit Drehknopf und Taster) kennen gelernt. Das was ich in die Finger bekommen (und aufgeschraubt) habe, hat einen Chip #CH552. Ich dachte es ist ein spezieller Tastaturchip wie der #CH340 ein USB-#UART Chip ist. Weit gefehlt, das ist ein #8051 kompatibler Chip mit USB, und der wird vom SDCC unterstützt!

ähnliches Macropad: github.com/wagiminator/CH552-M

SDCC Projekt: github.com/atc1441/CH55xOneCli

GitHubGitHub - wagiminator/CH552-MacroPad-plus: Programmable MacroPad with Rotary Encoder and NeoPixelsProgrammable MacroPad with Rotary Encoder and NeoPixels - wagiminator/CH552-MacroPad-plus
#DIY#TODO
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Sunflower Björnskalle 🌻

The rest of this information in more user-friendly but still somewhat confusng format can be found here:
raspberrypi.com/documentation/

I forgot to say that the mini UART also has smaller buffers than the PL011 but I guess that's obvious for anything less than a 16550. It says the latter has 32×8 though.

#linux#raspberrypi#serial
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Sunflower Björnskalle 🌻

Neither of the UARTs has DCD, DSR, DTR or RI signals so I guess that means they're not meant for real RS-232 even with a level a converter or driver but I don't know. I'm not that old. 😝

The manual for the PL011 is developer.arm.com/documentatio

The manual for the "mini UART" is part of that old "BCM2835 ARM Peripherals" document which you can find here. datasheets.raspberrypi.com/bcm

developer.arm.comDocumentation – Arm Developer
#linux#raspberrypi#serial
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Sunflower Björnskalle 🌻

So, for the Zero W, in order to use the UART, then you need to set enable_uart=1 and this will fix the VPU frequency to 250MHz so that it can be used.
You can actually force the Zero W to use the PL011 as it's primary UART by disabling #Bluetooth using a devicetree overlay. You can also force bluetooth to use the mini-UART instead of the PL011 using a devicetree overlay but this seems like a terrible idea.

#linux#raspberrypi#serial
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Sunflower Björnskalle 🌻

The primary UART is defined to be the one exposed on GPIO 14 (UART TX, i.e. pin 8) and GPIO 15 (UART RX, i.e. pin 10) and this is where Linux serial console is. The secondary UART is not normally exposed on the GPIO pins and is connected to the #Bluetooth side of the wireless chip if one is present.

The trick is that which UART is primary and secondary varies by device. On the Zero, the primary UART is the PL011 but on the Zero W, it's the mini UART.

#linux#raspberrypi#serial
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Sunflower Björnskalle 🌻

So, the Raspberry Pi Zero and Zero W both have two seperate UARTs. One is a PL011 which is a fully capable 16550-compatible UART made by ARM. The other is a "mini UART" which has no break detection, no framing error detection, no parity bit, no receive timout interrupt and its baud rate is tied to the frequency of the VPU (which needs to be configured to be fixed so that its baud rate doesn't vary.)

#linux#raspberrypi#serial
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RyeNCode 🇨🇦

So.. be sure that all (3) of the #uart pins are solidly connected. Seems one was, at best, intermittently connected and thus the serial terminal was often polluted with garbage. Once that issues was rectified it looks a little better.
I'm cutting my UART and #uboot teeth with a 2nd hand #fingbox before moving on to the main event.
Learning what I need to do to dump the current firmware before messing with what is there.

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Wintermute_BBS

It's hot, I hate it - so I turn my attention the the #Intel 8251 #UART which is being used in the MT Telcom II #modem #cartridge for #MSX systems.

I've already converted the cartridge to make use of an #esp8266 with #Zimodem firmware and desoldered the relays etc. (see here: github.com/dromorobo/MSX-wifi)

I guess it shouldn't be too much of a hassle to adapt my existing #Forth #code to that chip - that way I could have a very, very simplistic terminal program similar to the one that is included in the cartridge firmware. But unlike the firmware one, the Forth code would offer the chance to add minimalistic terminal emulation and hardware #flowcontrol.

Sounds like a nice rabbit hole to fall into - not that anyone would need such a software. But I could do it and I wonder wether I should ...

#MSX
#WifiModem
#Terminal
#Software
#RetroComputing
#RetroCoding

GitHubGitHub - dromorobo/MSX-wifi: MSX wifi (ESP8266 via RS232)MSX wifi (ESP8266 via RS232). Contribute to dromorobo/MSX-wifi development by creating an account on GitHub.
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