... > >> This calculation is actually wrong by factor 1000. A 20MHz SPI bus is not > >> really slow and it will transfer ~2.5MB/s over a single lane. > >> The calculation would be right for 20kHz but I think this is a more > >> esoteric case, isn't it? > > > > Some of the sums are wrong, but the conclusion might be right. > > A 4MB transfer at 20MHz only has 5 clocks/byte - seems low if it > > is only using 1 data bit. > > Can't really follow. Each data bit requires one clock on single wire > SPI. Adressing and the like may require a bit of overhead but that > should not be that much (12.5%?). That is for 4MB in one second at 20MHz. An SPI read transfer can be pretty much any length - you just keep on clocking out data. The overhead is independent of the length. A memory cell just reminded me that some SPI devices are made of two (or more) memory blocks - and you can't do sequential reads from one block to the next. (It might be lying...) David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
