Atmel SAM Approach¶

This page describes a proposed approach of implementing the E1 adapter using osmo-e1-xcvr and an Atmel SAMx microcontroller, suhc as a SAM3S or SAM4S.

• SAM4S Manual (64 MHz Cortex-M3)
• SAM4S Manual (120 MHz Cortex-M4)

Overview¶

• the SAM controls the LIU via SPI
• the SAM attaches to the host via USB
• The SAM SSC Peripheral is used to interface to the receive + transmit bit-streams of the LIU
• The SAM3 TC Peripheral is used for Rx frame alignment

Serializing/Deserializing¶

• SSC can receive/transmit synchronous serial bit streams with external or internal clock
• SSC supports DMA operation between the (de)serializer and RAM using PDC (peripheral DMA controller)
• SSC can run either
  • continously (frame alignment done in software [possibly using bit-banding], as no octet alignment of frames), or
  • triggered by RF input, which we supply from SSC (see below) with hardware-assisted frame alignment

Frame Alignment using TC (Timer/Counter)¶

The idea is to use one of the TC units to perform hardware-assisted frame alignment and this way prevent us from having to do tons of bit-shifting in software in order to align the start of the 256 bit E1 frame with an octet boundary.

• received clock is fed into TCLKx
• internal 16-bit counter is set to count up to 256 (one frame duration)
• TC is operated in WAVEFORM mode
• TIOA or TIOB are operated as output routed to the SSC RF (receive frame) input
• Ra/Rb/Rc registers are used to shift the rising and falling edge of the TIOA/TIOB signal within the 256bit frame