regdogg/mst703-lf_cfw

Custom Firmware for Microstar LCD controllers

MSTAR LCD Controller Firmware

Working source code / firmware for the MST70*-lf series of MSTAR Video/LCD controller IC's: This has currently been tested with the following IC's:

• MST703-LF
• MST705-LF
• MST706-LF

Use google to find the appropriate datasheet for the chip you're using, i.e., for the pinouts, but the configuration register settings for all of these should be more/less the same.

The primary goal of this repo is to focus mainly on small controller boards w/ 4"-7" TTL TFT LCD's used in analog FPV video transmissions. Thus, I've modified the firmware for simplicity, stability, and full support for 'snow' static in low / no-signal conditions. I've also removed many of the extra features that aren't needed for this application.

FYI, this is all still a work in progress, so use at your own risk...

Help is wanted/welcome, for those interested in joining the effort.

CONFIGURING

The proper PCB board & LCD types & options need to be configured before starting the build. The relevant config options can be found in the following files:

• board.h (where you can configure basic global board options & add new board definitions)
• panel.h (where you can add new LCD panel definitions)

Each board / LCD definition file will have various config options that can vary based on the specific board layout & LCD type. Eventually, I plan to add templates & build images for the most common PCB board & LCD screen combinations.

BUILDING

The source code is setup as a Keil uVision project. You must install Keil in order to build the binary firmware image. Eventually, I might look into porting the project over to SDCC, which is a free, open-source alternative to Keil, but it's not worth the effort right now. I, myself, run Keil via 'wine' within a linux environment, but running Keil in Windows should work as well.

The goal of the build process is to create a binary image file that matches the size of the external EEPROM flash chip mounted on a particular LCD controller board. In most cases, this should be either a 128k, or, in some cases, a 64k chip. Once the binary image file has been successfully built, it must be flashed to the EEPROM chip.

FLASHING

The EEPROM flash chip on the LCD board must be flashed with the built binary image. There are various ways to achieve this goal:

• removing / desoldering the SOIC-8 SPI flash chip and using an external programmer to flash it (Arduino, Bus Pirate, etc.)
• MSTAR programming tool & software
• DIY programming dongle & MSTAR ISP software
• Raspberry Pi & 'flashrom' utility (My preferred method; see below)

Using an RPi to flash

The MSTAR chips expose an i2c bus for ISP programming that can be accessed over the UART pins. By connecting these pins to the native i2c bus on a Raspberry Pi, it's possible to use the flashrom utility in order to program the flash chip.

The basic flashrom commands are as follows:

# read/backup an SPI flash chip to a file
flashrom -p mstarddc_spi:dev=/dev/i2c-1:0x49 -r backup_image.bin

# verify a previously-read image file
flashrom -p mstarddc_spi:dev=/dev/i2c-1:0x49 -v backup_image.bin

# write an image file to flash
flashrom -p mstarddc_spi:dev=/dev/i2c-1:0x49 -w firmware_image.bin 

MAKE SURE TO CREATE A BACKUP IMAGE OF YOUR STOCK FIRMARE & VERIFY IT BEFORE ATTEMPTING TO FLASH A CUSTOM IMAGE!!!

BASIC WORKING CONCEPTS

The MSTAR ASICs have an embedded 8051 microcontroller that is used to configure various internal configuration registers that control the behavior of the video decoder & LCD driver. On startup, these configuration registers need to be correctly initialized based on the PCB layout, LCD type&size, and incoming signal type&port. Also, the configuration needs to be constantly monitored & adjusted based on the condition of the incoming video signal. Keypad inputs are also monitored for handling features such as the built-in OSD & 'input select' functionality.

The MSTAR chips also expose GPIO & PWM functionality on certain pins which can be used to control external devices such as an LCD backlight, video tuner/receiver, LED's, etc.