EM357-RTR datasheet(26/241 Pages) SILABS

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Rev 1.3

4.4. Integrated MAC Module

The EM35x integrates most of the IEEE 802.15.4-2003 MAC requirements in hardware. This allows the ARM®

CortexTM-M3 CPU to provide greater bandwidth to application and network operations. In addition, the hardware

acts as a first-line filter for unwanted packets. The EM35x MAC uses a DMA interface to RAM to further reduce the

overall ARM® CortexTM-M3 CPU interaction when transmitting or receiving packets.

When a packet is ready for transmission, the Ember software configures the TX MAC DMA by indicating the packet

buffer RAM location. The MAC waits for the backoff period, then switches the baseband to TX mode and performs

channel assessment. When the channel is clear the MAC reads data from the RAM buffer, calculates the CRC, and

provides 4-bit symbols to the baseband. When the final byte has been read and sent to the baseband, the CRC

remainder is read and transmitted.

The MAC is in RX mode most of the time. In RX mode various format and address filters keep unwanted packets

from using excessive RAM buffers, and prevent the CPU from being unnecessarily interrupted. When the reception

of a packet begins, the MAC reads 4-bit symbols from the baseband and calculates the CRC. It then assembles the

received data for storage in a RAM buffer. RX MAC DMA provides direct access to RAM. Once the packet has

been received additional data, which provides statistical information on the packet to the Ember software, is

appended to the end of the packet in the RAM buffer space.

The primary features of the MAC are as follows:



CRC generation, appending, and checking



Hardware timers and interrupts to achieve the MAC symbol timing



Automatic preamble and SFD pre-pending on TX packets



Address recognition and packet filtering on RX packets



Automatic acknowledgment transmission



Automatic transmission of packets from memory



Automatic transmission after backoff time if channel is clear (CCA)



Automatic acknowledgment checking



Time stamping received and transmitted messages



Attaching packet information to received packets (LQI, RSSI, gain, time stamp, and packet status)



IEEE 802.15.4-2003 timing and slotted/unslotted timing

4.5. Packet Trace Interface (PTI)

The EM35x integrates a true PHY-level PTI for effective network-level debugging. It monitors all the PHY TX and

RX packets between the MAC and baseband modules without affecting their normal operation. It cannot be used to

inject packets into the PHY/MAC interface. This 500 kbps asynchronous interface comprises the frame signal

(PTI_EN, PA4) and the data signal (PTI_DATA, PA5). PTI is supported by the Ember development tools.

4.6. Random Number Generator

Thermal noise in the analog circuitry is digitized to provide entropy for a true random number generator (TRNG).

The TRNG produces 16-bit uniformly distributed numbers. The Ember software uses the TRNG to seed a pseudo

random number generator (PRNG). The TRNG is also used directly for cryptographic key generation.

EM357-RTR 数据表(PDF) 26 Page - Silicon Laboratories

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