After several months of work...
Trying various micro controllers and designs. I think I found the optimal hardware to overlay text over an NTSC or PAL video signal in 2020.
Less is Sometimes More
The ARM Cortext M0+ may not be the most powerful MCU on the market, but it offers one key advantage over an ARM Cortex M4, M3 or even an M0. It uses a 2 stage pipeline, rather than the 3 stage used in the other variants. While this was done primarily for power savings, it also makes the timing for entering an interrupt routine much more predictable, reducing jitter. The ST Micro variant (STM32G071) I chose has a 64 bit access to flash. The MCU read instructions 64 bits at a time into a cache making it possible to read the flash without stalling the program provided you time it just right.
MAX7456 Compatibility
The MODD OSD SPI interface and firmware is write compatible with the MAX7456 register set. This allows for software written for MAX7456 to just work without any modifications. Advanced MODD OSD features can be unlocked as needed by simply writing to registers that a 7456 chip ignores.
Advanced Features
The MODD OSD solution offers features not offered anywhere else. Double buffered graphics are now possible, as is greyscale. You are no longer limited to a black and white text only interface. Other features include Interlace mode that doubles the vertical resolution allowing you to pack more information on the screen.
Low Cost of Goods, Smaller Size.
With a hardware COG of around $1.50 at volume, ModdOSD costs less than other major components on a FC. No crystal is require when using with betaflight.
Trying various micro controllers and designs. I think I found the optimal hardware to overlay text over an NTSC or PAL video signal in 2020.
Less is Sometimes More
The ARM Cortext M0+ may not be the most powerful MCU on the market, but it offers one key advantage over an ARM Cortex M4, M3 or even an M0. It uses a 2 stage pipeline, rather than the 3 stage used in the other variants. While this was done primarily for power savings, it also makes the timing for entering an interrupt routine much more predictable, reducing jitter. The ST Micro variant (STM32G071) I chose has a 64 bit access to flash. The MCU read instructions 64 bits at a time into a cache making it possible to read the flash without stalling the program provided you time it just right.
MAX7456 Compatibility
The MODD OSD SPI interface and firmware is write compatible with the MAX7456 register set. This allows for software written for MAX7456 to just work without any modifications. Advanced MODD OSD features can be unlocked as needed by simply writing to registers that a 7456 chip ignores.
Advanced Features
The MODD OSD solution offers features not offered anywhere else. Double buffered graphics are now possible, as is greyscale. You are no longer limited to a black and white text only interface. Other features include Interlace mode that doubles the vertical resolution allowing you to pack more information on the screen.
Low Cost of Goods, Smaller Size.
With a hardware COG of around $1.50 at volume, ModdOSD costs less than other major components on a FC. No crystal is require when using with betaflight.