Blast processing
From Sega Retro
Blast Processing was a marketing term coined by Sega to advertise the faster processing performance of the Mega Drive/Genesis. Sonic the Hedgehog 2 was the posterboy for this campaign, being faster than any other platform game at the time. The ad campaign featured commercials with races between two vehicles, with the SNES strapped to one and the Mega Drive strapped to the other.
Technical details
The term was used to refer to two things that gave the Mega Drive/Genesis a faster performance:
- The fact that the main CPU processor was clocked over two times faster than the one in its rival product, the Super NES. Sega's Motorola 68000 processor was clocked at 7.67 MHz, compared to the 3.58 MHz clock speed of Nintendo's Ricoh 5A22 processor. However, this was slightly misleading. This idea of simply comparing CPU clock rates to determine performance, regardless of other characteristics, is commonly known as the "megahertz myth". While Nintendo's 5A22 did run slower in clock cycles per second, it would put out more instructions per clock cycle, giving it a similar MIPS (million instructions per second) performance to Sega's 68000. The 68000's faster performance came from other advantages, such as a wider 16-bit data bus (the SNES CPU had an 8-bit data bus), faster memory bus bandwidth, more registers, 32-bit instructions,[1] and shared codebase with arcade games (where the 68000 saw widespread use). For more details on the Mega Drive's CPU and memory, see Sega Mega Drive: Technical specifications.
- The fact that the Sega Mega Drive's Yamaha YM7101 VDP graphics chipset had a powerful DMA controller that could handle DMA (direct memory access) operations at a faster speed than the Super Nintendo's Ricoh PPU graphics chipset.[1] The Mega Drive/Genesis could write to VRAM during active display and VBlank,[2] and had a faster VRAM bandwidth than the SNES. The quicker DMA transfer rates and bandwidth gave the Mega Drive/Genesis a faster performance over the SNES.[3] This included a higher fillrate, higher gameplay resolution, faster scrolling, high frame-rate with many moving objects on screen, and programmable capabilities such as mid-frame palette swaps (increasing colors per scanline), direct color mode (increasing colors on screen), scaling and rotation effects, ray casting, bitmap framebuffer, and 3D polygon graphics; the stock Mega Drive hardware (without needing any enhancement chips) could render 3D polygons with a performance comparable to the Super FX enhancement chip [4][5] (itself outperformed by the Mega Drive's optional Sega Virtua Processor enhancement chip). For more details on the Mega Drive's DMA capabilities, see Sega Mega Drive: Blast Processing.
Origins of term
According to Sega staff involved in its development and marketing, it was the high-speed DMA controller, rather than the CPU MHz, that the term was actually referring to. According to Sega of America's former technical director Scot Bayless: [6]
| “ | So during the runup to the western launch of Sega-CD the PR guys interviewed me about what made the platform interesting from a technical standpoint and somewhere in there I mentioned the fact that you could just "blast data into the DAC's". Well they loved the word 'blast' and the next thing I knew Blast Processing was born. | „ |
— Scot Bayless | ||
One of the specific DMA programming techniques he was referring to was the mid-frame palette swap, where the color could be changed every scanline, increasing the colors displayed on screen, a technique that was used in Sonic 2: [7]
| “ | Marty Franz [Sega technical director] discovered that you could do this nifty trick with the display system by hooking the scan line interrupt and firing off a DMA at just the right time. The result was that you could effectively jam data onto the graphics chip while the scan line was being drawn – which meant you could drive the DAC's with 8 bits per pixel. Assuming you could get the timing just right you could draw 256 color static images. There were all kinds of subtleties to the timing and the trick didn't work reliably on all iterations of the hardware but you could do it and it was cool as heck. | „ |
— Scot Bayless | ||
References
- ↑ 1.0 1.1 http://trixter.oldskool.org/2008/12/05/blast-processing-101/
- ↑ http://emu-docs.org/Genesis/sega2f.htm
- ↑ http://www.gamepilgrimage.com/content/sega-genesis-vs-super-nintendo
- ↑ 3D math engine, SGDK
- ↑ Star Fox 3D Tech Demo on Sega Genesis: Version 2 Using DMA, YouTube
- ↑ [Damien McFerran, "Retroinspection: Mega-CD", Retro Gamer, issue 61, page 84 Damien McFerran, "Retroinspection: Mega-CD", Retro Gamer, issue 61, page 84]
- ↑ The Man Responsible For Sega's Blast Processing Gimmick Is Sorry For Creating "That Ghastly Phrase", Nintendo Life
External links
<mediaplayer>File:Blast Processing Commercial.flv</mediaplayer>
