Border support for 224p and 240p modes to achieve correct aspect ratio

[MarkTreeSMS]

Many thanks for the previous update to add 192p borders allowing for correct PAL aspect ratios.

The implementation of borders appears to only function at 192p.
Currently 224p and 240p do not have borders via analogue output and so do not match original hardware, and will thus also remain at an incorrect aspect ratio over HDMI.

Additionally:

• 240p output appears to have a vertical shift with respect to original hardware
• 240p Runs at 52.4Hz rather than the standard SMS PAL of 49.7Hz

Related previous issues: #120 #123

Images illustrating the differences to Original Hardware and MiSTer behaviour below:

Original Hardware:
224p displayed via "Micro Machines" on SMSII Hardware over RF

MiSTer Core on latest revision:
224p displayed via "Micro Machines" on MiSTer via RGB SCART

192p via Maxim's 240 tester rom on MiSTer via RGB SCART and HDMI (correct behaviour)

224p via Maxim's 240 tester rom on MiSTer via RGB SCART and HDMI (no borders as noted in Micro Machines, incorrect aspect ratio over HDMI)

240p via Maxim's 240 tester rom on MiSTer via RGB SCART and HDMI (no borders?, odd 52.4Hz, incorrect aspect ratio over HDMI)

Additional notes:

• Clear view of "up" shift in 240p MiSTer output noting the bottom of the image on CRT is the same as 224p. On SMSII the image remains vertically centred at 192p, 224p and 240p.
• 240p appears to also have no border, HDMI image retains the same size on the display as 224p so is also clearly in error. The absence of border colour from tester ROM makes this otherwise hard to determine.
• The vertical offset of all MiSTer output on my CRT compared to SMSII is entirely due to the RGB SCART to RF input difference and is not an issue

Thanks very much!

[birdybro]

Thank you for the thorough testing and documentation of this.