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fm-br23.md

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FM radio (BR23, BR25)

FM receiver

FM transmitter

The FM transmitter block reads audio data from memory and outputs a multiplex signal in form of a 32-bit value (usually interpreted as a 8.24 fixed point number) to the frequency synthesizer that generates the frequency-modulated carrier.

The memory buffer format is a stereo 16-bit linear PCM with 41666.(6) Hz sampling rate.

output = TX_FREQ + ((Left + Right) / 256 + Pilot19 * TX_PILOT + (Left - Right) * Carrier36 / 256) * TX_MUL * TX_SYN_GAIN / 4096

Registers

  • FM receiver:
Offset Name Description
0x00 CON Control register
0x04 BASE RX DMA buffer base address
0x08 ADC_CON
0x0C ADC_CON1
0x10 HF_CON0
0x14 HF_CON1
0x18 HF_CRAM
0x1C HF_CRAM2
0x20 HF_DRAM
0x24 LF_CON
0x28 LF_RES
0x2C FMRX_CON4
0x30 FMRX_CON5
  • FM transmitter:
Offset Name Description
0x34 TX_CON0 TX control register 1
0x38 TX_CON1 TX control regsiter 2
0x3C TX_PILOT Pilot tone gain
0x40 TX_SYN_GAIN Synth gain 1
0x44 TX_MUL Multiplier
0x48 TX_ADR ireg address
0x4C TX_LEN buffer length / ireg value
0x50 TX_FREQ base frequency
0x54 TX_BASE_ADR DMA buffer base address
  • Analog part: (in JL_ANA)
Offset Name Description

CON

Bits Type Name Default Description
14 R/W Setting this to '0' enables TX related registers
3 R/W
0 R/W

HF_CON1

Bits Type Name Default Description
7 R PND Interrupt pending
6 W CPND Clear pending interrupt
4 R DMA buffer slice index (buffer index that has been filled now)

TX_CON0

Bits Type Name Default Description
7 R/W enable2
5 W Something write strobe
4 R DMA buffer slice index (buffer index that can be filled now)
3 R/W
1 R/W Enable stereo
0 R/W enable1

TX_CON1

Bits Type Name Default Description
7 R PND Interrupt pending
6 W CPND Clear pending interrupt
3:0 R/W

TX_PILOT

Bits Type Name Default Description
12:0 R/W Pilot tone gain

TX_SYN_GAIN

Bits Type Name Default Description
12:0 R/W Synth gain 1 (4096 = 1.0)

TX_MUL

Bits Type Name Default Description
..:0 R/W multipler

TX_FREQ

Bits Type Name Default Description
31:24 R/W Integer part
23:0 R/W Fractional part