Atmel SAM Approach » History » Revision 4
Revision 3 (laforge, 05/04/2018 09:58 PM) → Revision 4/10 (laforge, 05/04/2018 10:11 PM)
h1. 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. * "SAM3S Manual":http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-6500-32-bit-Cortex-M3-Microcontroller-SAM3S4-SAM3S2-SAM3S1_Datasheet.pdf (64 MHz Cortex-M3) * "SAM4S Manual":http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-11100-32-bit%20Cortex-M4-Microcontroller-SAM4S_Datasheet.pdf (120 MHz Cortex-M4) h2. 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 h2. 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 h2. 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 h2. Transmit side The transmit side is rather simple: * use either recovered Rx clock or locally-generated clock (from GPS-DO) * serialize the bits with no particular alignment requirements, as it's entirely up to the receiver to align to the frames we send
