Tosta is a low-power terminal interface module built around the STM32G030 microcontroller. The module features:
- 48x84 monochrome pixel matrix (Nokia 5510 LCD using PCD8544 controller)
- configurable dimmable backlight
- configurable display standby timer
- a rotary encoder with central switch
- a D-Pad joystick with central switch
- 4 tactile switches
- a speaker
- an UART interface @ 115200 baud/s
- an I2C slave interface @ 400KHz (address 0x7D)
- 150uA consumption in standby mode
The main communication interface (characters based) is UART @ 115200 baud/s. I2C (binary based) is used for fast display update among other things.
When the module receive an input, it send a corresponding command character as follows:
| Event | Hex | Char |
|---|---|---|
| SW1 pressed | 0x41 | A |
| SW1 released | 0x61 | a |
| SW2 pressed | 0x42 | B |
| SW2 released | 0x62 | b |
| SW3 pressed | 0x43 | C |
| SW3 released | 0x63 | c |
| SW4 pressed | 0x44 | D |
| SW4 released | 0x64 | d |
| D-Pad button pressed | 0x45 | E |
| D-Pad button released | 0x65 | e |
| D-Pad left pressed | 0x46 | F |
| D-Pad left released | 0x66 | f |
| D-Pad right pressed | 0x47 | G |
| D-Pad right released | 0x67 | g |
| D-Pad up pressed | 0x48 | H |
| D-Pad up released | 0x68 | h |
| D-Pad down pressed | 0x49 | I |
| D-Pad down released | 0x69 | i |
| Encoder button pressed | 0x4A | J |
| Encoder button released | 0x6A | j |
| Encoder turn clockwise | 0x2B | + |
| Encoder turn anti-clockwise | 0x2D | - |
The display matrix comprises 84 horizontal by 48 vertical pixels. Each individual pixel is either on (1) or off (0) which corresponds to the status of a single bit. Individual bits are grouped into bytes, representing a sub-column of 8 pixels.
The next byte is the nearby sub-column, on the right side. The display frame buffer contains a total 504 bytes: 84 for the upper sub-columns, 84 for the next ones and so on, for a total of 6 (84x6 bytes, row-major ordering).
Characters are a logical subdivision into a 14x6 matrix, in which each cell is a 6x8 pixels sub-matrix (see blue lines).
h 0x7f 0x08 0x04 0x04 0x78 0x00
e 0x38 0x54 0x54 0x54 0x18 0x00
l 0x00 0x41 0x7f 0x40 0x00 0x00
l 0x00 0x41 0x7f 0x40 0x00 0x00
o 0x38 0x44 0x44 0x44 0x38 0x00
! 0x00 0x00 0x5f 0x00 0x00 0x00
Writing characters works as usual on a tty device, using standard ASCII encoding (printable characters from 0x20 up to 0x7F). There are few special characters:
\a(bell): play a C4 note from the speaker for 250ms\b(backspace): delete the last displayed character\n(line feed): newline\f(form feed): clear screen\r(carriage return): move cursor to the beginning of the current line
The user can also add non-standard custom characters (from 0x80 to 0xFF) using parametric escape sequences.
Escape sequences are used to obtain special behaviours. In order to start
an escape sequence, the special character \e (or \x1B or \033) must be
used.
Basic sequences are:
| Sequence | Effect |
|---|---|
\es |
Put the display in standby |
\ew |
Wake up the display from standby |
\el |
Display an awesome logo |
Advanced sequences allow passing numerical parameters, and they're started
using \e[ (i.e. \x1B[ or \033[).
| Sequence | Effect |
|---|---|
\e[Nb |
Set display backlight brightness, with N in [0, 127] |
\e[N,A,B,C,D,E,Fc |
Set user character N, specifying bytes in the character sub-matrix from left to right (N in [128, 255]; A,B,C,D,E,F in [0, 255]) |
\e[F,Tp |
Play sound (immediate) having frequency F for T milliseconds |
\e[F,Tq |
Enqueue sound playing with frequency F for T milliseconds |
\e[Ts |
Set the display standby timer in T milliseconds (0 to disable standby) |
\e[X,Yz |
Set cursor position to X in [0, 13] and Y in [0, 5] |
stty -F /dev/ttyUSB0 115200
echo -ne "\e[128,12,30,60,30,12,0c" >>/dev/ttyUSB0
echo -ne "\f\x80\x80\x80\x80\x80\x80\x80\x80\x80\x80\x80\x80\x80\x80Frere Jacques\n\x80\x80\x80\x80\x80\x80\x80\x80\x80\x80\x80\x80\x80\x80" >>/dev/ttyUSB0
echo -ne "\e[1047,500q\e[1175,500q\e[1319,500q\e[1047,500q\e[1047,500q\e[1175,500q\e[1319,500q\e[1047,500q\e[1319,500q\e[1397,500q\e[1568,500q\e[0,500q\e[1319,500q\e[1397,500q\e[1568,500q" >>/dev/ttyUSB0- Send 1 byte to address 0x7D for command (0), necessary to wake the MCU from stop mode nicely
- Send the framebuffer (504 bytes) to address 0x7D
- ...
Firmware is written using the STM32 Cube IDE.
- TIM1: speaker PWM
- TIM3: LCD backlight PWM
- TIM14: Inputs debounce
- SPI1+DMA: LCD data output
- UART: main serial communication interface
- I2C1: secondary communication interface (slave)
0x7D == ('t' ^ 'o' ^ 's' ^ 't' ^ 'a')