write some notes about hdmi

1 files changed, 39 insertions, 0 deletions

diff --git a/notes.md b/notes.md
index 344b1fa..f146ed4 100644
--- a/notes.md
+++ b/notes.md
@@ -48,3 +48,42 @@ Which file to include:
 | `suseconds_t`                          | `<sys/types.h>`                   | signed                         |
 | `clock_t`                              | `<sys/types.h>`                   | could be float                 |
 | `time_t`                               | `<sys/types.h>`                   | signed                         |
+
+
+Here's my reading of the lowest-bitrate possible for our HDMI sink:
+
+HDMI v1.4 (2009/06/05) § 6.2.1 "Format Support Requirements"
+
+>  - An HDMI Source shall support at least one of the following video
+>    format timings:
+>     + 640x480p @ 59.94/60Hz
+>     + 720x480p @ 59.94/60Hz
+>     + 720x576p @ 50Hz
+> …
+>
+> - An HDMI Sink that accepts 60Hz video formats shall support the
+>   640x480p @ 59.94/60Hz and 720x480p @ 59.94/60Hz video format
+>   timings
+>
+> - An HDMI Sink that accepts 50Hz video formats shall support the
+>   640x480p @ 59.94/60Hz and 720x576p @ 50Hz video format timings.
+
+These latter 2 requirements match what is in CEI-861-D §3.1 "General
+Video Format requirements" Table 1.
+
+I'm a little confused about the 50Hz systems requirement; if it
+needs to support 640x480@60Hz, does that mean that it's *also* a 60Hz
+system and must therefore also support 720x480@60Hz?
+
+Anyway, I need to support at least 640x480p@60Hz and 720x480@60Hz, and
+it would be nice to support 720x576p@50Hz.  Note that PicoDVI supports
+these first two, but not the @50Hz one.
+
+| format        | bitrate               |
+|---------------|-----------------------|
+| 640x480p@60Hz | 18,432,000 pixels/sec |
+| 720x480p@60Hz | 20,736,000 pixels/sec |
+| 720x576p@50Hz | 20,736,000 pixels/sec |
+
+https://forums.parallax.com/discussion/download/128730/Hdmi-1.4-1000008562-6364143185282736974850538.pdf
+https://ia803002.us.archive.org/1/items/CEA-861-D/CEA-861-D.pdf