[linux-dvb] bit error rate versus count - stv0299

["Michael Glaum" <mglaum@kvh.com>]

The way I read the API the FE_READ_BER should give you the
bit error _rate_, in some known units.

In the case of the stv0299 I notice that the chip is instead
being configured to _count_ Viterbi bit errors. Indeed, 0x93 is
written to register 0x34, the error control register:

bit		descr
7		1: Error Count
		0: Error Rate

[5:4]		00: QPSK bit errors
		01: Viterbi bit errors
		10: Viterbi byte errors
		11: packet errors

[1:0]		NOE bits [sic] in count Period in bytes (NB)
		00: 2^12 bytes
		01: 2^14 bytes
		10: 2^16 bytes
		11: 2^18 bytes

   To get a correct measurement of bit error rate, I think we
   should configure the stv0299 to calculate Viterbi bit
   error rates at 2^18 __bytes__. That is we should write 0x13
   in register 0x34. If we get number X from FE_READ_BER then
   the BER in dimensionless units is
		x/(8*2^18).

   Opinions anyone? Does anyone know what the other frontends
   are doing?

Index: stv0299.c
===================================================================
RCS file: /cvs/linuxtv/DVB/driver/frontends/stv0299.c,v
retrieving revision 1.7
diff -u -r1.7 stv0299.c
--- stv0299.c	8 May 2003 13:50:10 -0000	1.7
+++ stv0299.c	18 Jun 2003 19:35:17 -0000
@@ -157,7 +157,7 @@
 
 	0x32, 0x19,  // viterbi and synchro search
 	0x33, 0xfc,  // rs control
-	0x34, 0x93,  // error control
+	0x34, 0x13,  // error control
 
 	0x0b, 0x00,
 	0x27, 0x00,


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