Messages in this thread | | | From | "H. Peter Anvin" <> | Subject | Insanely high baud rates | Date | Tue, 9 Oct 2018 12:19:04 -0700 |
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[Resending to a wider audience]
In trying to get the termios2 interface actually implemented in glibc, the question came up if we will ever care about baud rates in excess of 4 Gbps, even in the relatively remote future.
If this is something we care about *at all*, I would like to suggest that rather than defining yet another kernel interface, we steal some bits from the MSB of the speed fields, alternatively one of the c_cc bytes (all likearchitectures seem to have c_cc[18] free) or some field, if we can find them, in c_cflags, to indicate an exponent.
With 5 bits from the top of the speed fields, the current values would be identical up to 248 Gbps, and values up to ~288 Pbps would be encodable ±2 ppb.
In the short term, all we would have to do in the kernel would be erroring out on baud rates higher than 0x0fffffff (2^28-1 due to implicit one aliasing rhe first bit of a 5-bit exponent – less than 2^27 are functionally denorms.) However, I'd like to put the glibc infrastructure for this now if this is something we may ever be interested in.
Thoughts? -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
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