MP Select Mini USART Interface

Pi ⟷ Mini UART connection.md

MP Select Mini

The serial cable (that ordinarily connects to the LCD controller) has four wires: Red, White, Green, Black.

• Red ➙ Ground
• White ➙ TX USART1 - pin 42†
• Green ➙ RX USART1 - pin 43†
• Black ➙ +3.3V (yup, they're backwards)

†: on the STM32 processor

(see notes)

Raspi (With PL011 exposed)

• Pin 6 (or 9, 14, ...) ➙ Ground
• pin 8 ➙ TX (GPIO14)
• pin 10 ➙ RX (GPIO15)
• pin 1 ➙ +3.3V†

†: You don't actually connect the 3.3v.

MPS mini ⟷ Raspi over serial

• pin 6 ⟷ Red Orange‡
• pin 8 ⟷ Green Green‡
• pin 10 ⟷ White Yellow‡

‡: the colors of the jumper wires on the cable I made.

pins 6,8,and 10 are a nice block on the outside row, skip two down.

Results (WiP)

I've successfully connected with:

• minicom
• octoprint
• pronterface(s)

All at 500k baud and with the 3.3V line left dettached.

I only had success after having the Pi and the Mini share ground off the same power supply.

The connection succeeds near-instantly every time and seems, so far, much more stable. I've hacked pronterface to ignore the non-gcode and completed prints without a glitch.

Proto over serial.md

serial_init    
SetSysTick     
RetrieveSettings
port_init      
LED_ON         
ENDSTOP P TRIGGERED
ENDSTOP P TRIGGERED
setup          
���Ӻ�����������Һ����Һ���

The garbage on the last line is fbd3d9d3bad3d4c1d2d4c5c4fdfbd6c5d2bab4b0fdfbd2bad5c4fd in hex.

Doesn't look very random. They're all really high. Flip the first bit of each byte and you get ASCII back. Following setup is {SYS:STARTED}{VER:40}{R:UD} which looks like the codes mentioned here and reported there.

I also see FBD3D9D3BAC2D5C9CCC4FD which is SYS:BUILD} a bunch. I don't know what happened to the leading '{'.

stty ⁄ setserial Reports.md

Pi Zero W w/ Octopi

ttyS0 - 16550 (mini-UART)

setserial -a

$ sudo setserial -a /dev/ttyS0
/dev/ttyS0, Line 0, UART: 16550, Port: 0x0000, IRQ: 214
        Baud_base: 31250000, close_delay: 50, divisor: 0
        closing_wait: 3000
        Flags: spd_normal skip_test

Idle

$ sudo stty -F /dev/ttyS0
speed 9600 baud; line = 0;
-brkint -imaxbel

Running a getty:

$ sudo stty -F /dev/ttyS0 
speed 115200 baud; line = 0;
min = 1; time = 0;
-brkint -icrnl -imaxbel iutf8
-isig -icanon -iexten -echo -echoe -echok -echoctl -echoke

ttyACM0 - MP USB

setserial -a

$ sudo setserial -a /dev/ttyACM0 
/dev/ttyACM0, Line 0, UART: unknown, Port: 0x0000, IRQ: 0
        Baud_base: 9600, close_delay: 5, divisor: 0
        closing_wait: 300
        Flags: spd_normal low_latency

Unlike the others, Baud_base is 9600 initially but changes based on connection attempts.

Idle

$ sudo stty -F /dev/ttyACM0 
speed 9600 baud; line = 0;
-brkint -imaxbel

After a failed auto-baud detect run

$ sudo stty -F /dev/ttyACM0 
speed 9600 baud; line = 0;
min = 0; time = 0;
-brkint -icrnl -imaxbel
-opost
-isig -icanon -iexten -echo -echoe -echok -echoctl -echoke

Successfully connected

$ sudo stty -F /dev/ttyACM0
speed 115200 baud; line = 0;
min = 0; time = 0;
-brkint -icrnl -imaxbel
-opost
-isig -icanon -iexten -echo -echoe -echok -echoctl -echoke

ttyAMA0 - PL011

setserial -a

$ sudo setserial -a /dev/ttyAMA0 
/dev/ttyAMA0, Line 0, UART: undefined, Port: 0x0000, IRQ: 81
        Baud_base: 3000000, close_delay: 50, divisor: 0
        closing_wait: 3000
        Flags: spd_normal

There are three red flags (herrings?) that will probably come up:

• UART: undefined as reported by set serial above.
• After loading the AMBA PL011 UART driver, the console will print uart-pl011 20201000.serial: could not find pctldev for node /soc/gpio@7e200000/uart0_pins, deferring probe
• When accessed, the console will print uart-pl011 20201000.serial: no DMA platform data These all seem to be expected on a Pi and won't block connecting.

Idle

$ sudo stty -F /dev/ttyAMA0 
speed 9600 baud; line = 0;
-brkint -imaxbel

Controlled by BT system

$ sudo stty -F ttyAMA0
speed 3000000 baud; line = 15;
min = 1; time = 0;
-brkint -icrnl -imaxbel
-opost
-isig -icanon -iexten -echo 

Connected to MP Select Mini

$ sudo stty -F /dev/ttyAMA0 
speed 500000 baud; line = 0;
min = 0; time = 0;
-brkint -icrnl -imaxbel
-opost -onlcr
-isig -icanon -iexten -echo -echoe -echok -echoctl -echoke