Posts Tagged ‘BERT Function
Each integrated T1/E1 transceiver contains a BERT. The BERT block can generate and detect pseudorandom and repeating bit patterns. It is used to test and stress data communication links, and it is capable of generating and detecting the following patterns:
- The pseudorandom patterns 2E7, 2E11, 2E15, and QRSS
- A repetitive pattern from 1 to 32 bits in length
- Alternating (16-bit) words that flip every 1 to 256 words
- Daly pattern
The BERT receiver has a 32-bit bit counter and a 24-bit error counter. The BERT receiver reports three events: a change in receive synchronizer status, a bit error being detected, and if either the bit counter or the error counter overflows. Each of these events can be masked within the BERT function through the BERT control register 1(TR.BC1). If the software detects that the BERT has reported an event, then the software must read the BERT information register (BIR) to determine which event(s) has occurred. To activate the BERT block, the host must configure the BERT mux through the TR.BIC register.
1. BERT Status
TR.SR9 contains the status information on the BERT function. The host can be alerted through this register when there is a BERT change-of-state. A major change-of-state is defined as either a change in the receive synchronization (i.e., the BERT has gone into or out of receive synchronization), a bit error has been detected, or an overflow has occurred in either the bit counter or the error counter. The host must read status register 9(TR.SR9) to determine the change-of-state.
2. BERT Mapping
The BERT function can be assigned to the network direction or backplane direction through the direction control bit in the BIC register (TR.BIC.1). See Figure 1 and Figure 2. The BERT also can be assigned on a per channel basis. The BERT transmit control selector (BTCS) and BERT receive control selector (BRCS) bits of the per-channel pointer register (TR.PCPR) are used to map the BERT function into time slots of the transmit and receive data streams. In T1 mode, the user can enable mapping into the F-bit position for the transmit and receive directions through the RFUS and TFUS bits in the BERT interface control (TR.BIC) register.
Figure 1. Simplified Diagram of BERT in Network Direction
Figure 2. Simplified Diagram of BERT in Backplane Direction
3. BERT Repetitive Pattern Set
These registers must be properly loaded for the BERT to generate and synchronize to a repetitive pattern, a pseudorandom pattern, alternating word pattern, or a Daly pattern. For a repetitive pattern that is fewer than 32 bits, the pattern should be repeated so that all 32 bits are used to describe the pattern. For example, if the pattern was the repeating 5-bit pattern …01101… (where the rightmost bit is the one sent first and received first), then TR.BRP1 should be loaded with ADh, TR.BRP2 with B5h, TR.BRP3 with D6h, and TR.BRP4 with 5Ah. For a pseudorandom pattern, all four registers should be loaded with all 1s (i.e., FFh). For an alternating word pattern,one word should be placed into TR.BRP1 and TR.BRP2 and the other word should be placed into TR.BRP3 and TR.BRP4. For example, if the DDS stress pattern “7E” is to be described, the user would place 00h in TR.BRP1,00h in TR.BRP2, 7Eh in TR.BRP3, and 7Eh in TR.BRP4 and the alternating word counter would be set to 50(decimal) to allow 100 bytes of 00h followed by 100 bytes of 7Eh to be sent and received.
4. BERT Bit Counter
The BERT Bit Counter is comprised of TR.BBC1, TR.BBC2, TR.BBC3, and TR.BBC4. Once BERT has achieved synchronization, this 32-bit counter increments for each data bit (i.e., clock) received. Toggling the LC control bit inTR.BC1 can clear this counter. This counter saturates when full and sets the BBCO status bit.
5. BERT Error Counter
The BERT Error Counter is comprised of TR.BEC1, TR.BEC2, and TR.BEC3. Once BERT has achieved synchronization, this 24-bit counter increments for each data bit received in error. Toggling the LC control bit inTR.BC1 can clear this counter. This counter saturates when full and sets the BECO status bit.
6. BERT Alternating Word-Count Rate
When the BERT is programmed in the alternating word mode, each word repeats for the count loaded intoTR.BAWC. One word should be placed into TR.BRP1 and TR.BRP2 and the other word should be placed intoTR.BRP3 and TR.BRP4.