1.1 --- a/ULA.txt Wed Apr 15 22:31:08 2020 +0200
1.2 +++ b/ULA.txt Thu Apr 16 00:24:51 2020 +0200
1.3 @@ -251,6 +251,27 @@
1.4 2MHz RAM Access enhancement below for bandwidth calculations that consider
1.5 this limitation removed.
1.6
1.7 +A summary of the bandwidth figures is as follows (with extra timing details
1.8 +described below):
1.9 +
1.10 + Standard ULA % Total Slowdown BBC-10s BBC-34s
1.11 +MODE 0, 1, 2 9728 bytes 24% 4.11 43s 105s
1.12 +MODE 3 12288 bytes 31% 3.25 34s
1.13 +MODE 4, 5 19968 bytes 50% 2 20s
1.14 +MODE 6 19968 bytes 50% 2 20s 50s
1.15 +
1.16 +The review of the Electron in Practical Computing (October 1983) provides a
1.17 +concise overview of the RAM access limitations and gives timing comparisons
1.18 +between modes and BBC Micro performance. In the above, "BBC-10s" is the
1.19 +measured or stated time given for a program taking 10 seconds on the BBC
1.20 +Micro, whereas "BBC-34s" is the apparently measured time given for the
1.21 +"Persian" program taking 34 seconds to complete on the BBC Micro, with a
1.22 +"quick" mode presumably switching to MODE 6 using the ULA directly in order to
1.23 +reduce display bandwidth usage while the program draws to the screen.
1.24 +Evidently, the measured slowdown is slightly lower than the theoretical
1.25 +slowdown, most likely due to the running time not being entirely dominated by
1.26 +RAM access performance characteristics.
1.27 +
1.28 Video Timing
1.29 ------------
1.30