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R820T调试笔记

发布时间 2023-07-21 09:15:44作者: SymPny

R820T芯片内部结构：

R820T配合RTL2832U的RTL-SDR：

软件无线电通过数字信号处理来实现无线信号的调制解调。在RTL-SDR中通过调谐芯片(R820T、E4000)将无线信号下变频至低中频信号，由RTL2832U中的ADC采样得到数字信号，再进行数字下变频得到基带信号，由USB传送给计算机。RTL-SDR得到的基带信号是I/Q信号交错排列的形式，计算机对基带信号进行分离得到两路信号即I/Q信号进行解调。

其简易电路图：

R820T寄存器配置：

在tuner_r82xx.c文件中，可以找到配置的默认值：

  1. /* Those initial values start from REG_SHADOW_START */
  2. static const uint8_t r82xx_init_array[NUM_REGS] = {
  3. 	0x83, 0x32, 0x75,			/* 05 to 07 */
  4. 	0xc0, 0x40, 0xd6, 0x6c,			/* 08 to 0b */
  5. 	0xf5, 0x63, 0x75, 0x68,			/* 0c to 0f */
  6. 	0x6c, 0x83, 0x80, 0x00,			/* 10 to 13 */
  7. 	0x0f, 0x00, 0xc0, 0x30,			/* 14 to 17 */
  8. 	0x48, 0xcc, 0x60, 0x00,			/* 18 to 1b */
  9. 	0x54, 0xae, 0x4a, 0xc0			/* 1c to 1f */
  10. };

根据R820T芯片手册，部分寄存器解释如下：

  1. ------------R5=0x83---------------
  2. [7]Loop through ON/OFF = off
  3. [5]LNA 1 power control = on
  4. [4]LNA gain mode switch = on
  5. [3:0]LNA manual gain control = 0011
  6. ------------R6=0x32--------------
  7. [7]Power detector 1 on/off = on
  8. [6]Power detector 3 on/off = off
  9. [5]Filter gain 3db = +3db
  10. [2:0]LNA power control = 010
  11. ------------R7=0x75---------------
  12. [6]Mixer power = on
  13. [5]Mixer current control = normal current
  14. [4]Mixer gain mode = auto mode
  15. [3:0]Mixer manual gain control = 0101
  16. ------------R8=0xc0---------------
  17. [7]Mixer buffer power on/off = on
  18. [6]Mixer buffer current setting = low current
  19. [5:0]Image Gain Adjustment = 0
  20. ------------R9=0x40----------------
  21. [7]IF Filter power on/off = filter on
  22. [6]IF Filter current = low current
  23. [5:0]Image Phase Adjustment = 0
  24. ------------R10=0xd6--------------
  25. [7]Filter power on/off = on
  26. [6:5]Filter power control = 10
  27. [4] 1
  28. [3:0]Filter bandwidth manual fine tune = 0110
  29. ------------R11=0x6c----------------
  30. [7] 0
  31. [6:5]Filter bandwidth manual course tunnel = middle
  32. [4] 0
  33. [3:0]High pass filter corner control = 1100
  34. ------------R12=0xf5-------------
  35. [6]VGA power control = vga power on
  36. [4]VGA GAIN manual / pin selector = IF vga gain controlled by vagc pin
  37. [3:0]IF vga manual gain control = 0101
  38. ------------R13=0x63--------------
  39. [7:4]LNA agc power detector voltage threshold high setting = 0110
  40. [3:0]LNA agc power detector voltage threshold low setting = 0011
  41. ------------R14=0x75--------------
  42. [7:4]MIXER agc power detector voltage threshold high setting = 0111
  43. [3:0]MIXER agc power detector voltage threshold low setting = 0110
  44. ------------R15=0x68---------------
  45. [4]Clock out pin control = clk output on
  46. [1]AGC clk control = internal agc clock on
  47. ------------R16=0x6c----------------
  48. [7:5]PLL to Mixer divider number control = mixer in = vco out
  49. [4]PLL Reference frequency Divider = fref=xtal_freq
  50. [1:0]Internal xtal cap setting = no cap
  51. ------------R17=0x83--------------
  52. [7:6]PLL analog low drop out regulator switch = 2.0V
  53. ------------R18=0x80---------------
  54. [7:6]PLL integer divider number input Si2c = 10
  55. [5:0]PLL integer divider number input Ni2c = 0
  56. --------------------------------------
  57. ------------R30=0x4a------------------
  58. [5:0]Power detector timing control = 001010
  59. [6]Filter extension under weak signal = Enable

librtlsdr.c文件修改较多，其中rtlsdr_read_array函数和rtlsdr_write_array函数需要重新配置为ZYNQ的I2C。

  1. int rtlsdr_read_array(rtlsdr_dev_t *dev, uint8_t block, uint16_t addr, uint8_t *array, uint8_t len)
  2. {
  3. 	int r;
  4. 	uint16_t index = (block << 8);
  5.  
  6. //	r = libusb_control_transfer(dev->devh, CTRL_IN, 0, addr, index, array, len, CTRL_TIMEOUT);
  7. 	r = test_i2c_read(dev->devh, addr, array, len);
  8. #if 0
  9. 	if (r < 0)
  10. 		fprintf(stderr, "%s failed with %d\n", __FUNCTION__, r);
  11. #endif
  12. 	return r;
  13. }
  14.  
  15. int rtlsdr_write_array(rtlsdr_dev_t *dev, uint8_t block, uint16_t addr, uint8_t *array, uint8_t len)
  16. {
  17. 	int r;
  18. 	if(IICB != block)
  19. 		return 0;
  20. //	uint16_t index = (block << 8) | 0x10;
  21. //	r = libusb_control_transfer(dev->devh, CTRL_OUT, 0, addr, index, array, len, CTRL_TIMEOUT);
  22. 	r = test_i2c_write(dev->devh, addr, array, len);
  23. #if 0
  24. 	if (r < 0)
  25. 		fprintf(stderr, "%s failed with %d\n", __FUNCTION__, r);
  26. #endif
  27. 	return r;
  28. }

在ZYNQ的main中执行如下，R820T即可输出波形：

  1. #include <stdio.h>
  2. #include "xparameters.h"
  3. #include "xil_cache.h"
  4. #include "xiic.h"
  5. #include "axi_reg.h"
  6. #include "xil_io.h"
  7. #include "xgpio.h"
  8. #include "tuner_r82xx.h"
  9. #include "rtl-sdr2.h"
  10.  
  11.  
  12. #define DEFAULT_FREQUENCY	(98*1000*1000)
  13. #define DEFAULT_SAMPLE_RATE 2048000
  14. XGpio gpio0, gpio1;
  15. XIic IIC;
  16. static rtlsdr_dev_t *rtlsdr_dev = NULL;
  17.  
  18. /*****************************************************************************/
  19. unsigned test_i2c_write(void *dev, u8 i2c_addr, u8 *buf, u16 len)
  20. {
  21. 	volatile unsigned SentByteCount;
  22. 	SentByteCount = XIic_Send(XPAR_IIC_0_BASEADDR, (i2c_addr>>1),
  23. 			buf, len, XIIC_STOP);
  24. 	return SentByteCount;
  25. }
  26.  
  27. unsigned test_i2c_read(void *dev, u8 i2c_addr, u8 *buf, u16 len)
  28. {
  29. 	volatile unsigned ReceivedByteCount;
  30. 	ReceivedByteCount = XIic_Recv(XPAR_IIC_0_BASEADDR, (i2c_addr>>1),
  31. 			buf, len, XIIC_STOP);
  32. 	return ReceivedByteCount;
  33. }
  34.  
  35. int interface_init() {
  36. 	int i;
  37. 	i = XIic_Initialize(&IIC, XPAR_IIC_0_DEVICE_ID);
  38. 	if (i != XST_SUCCESS) {
  39. 		return XST_FAILURE;
  40. 	}
  41. 	i = XGpio_Initialize(&gpio0, XPAR_GPIO_0_DEVICE_ID);
  42. 	if (i != XST_SUCCESS) {
  43. 		return XST_FAILURE;
  44. 	}
  45. 	XGpio_SetDataDirection(&gpio0, 1, 0xFF);
  46. 	return 1;
  47. }
  48.  
  49. int main ()
  50. {
  51. 	int r = 0;
  52. 	int gain = 0;
  53. 	int ppm_error = 0;
  54. 	uint32_t frequency = DEFAULT_FREQUENCY;//Hz
  55. 	uint32_t samp_rate = DEFAULT_SAMPLE_RATE;
  56.  
  57. 	r = interface_init();
  58. 	r = rtlsdr_open(&rtlsdr_dev, (uint32_t)0);
  59. 	r = rtlsdr_set_sample_rate(rtlsdr_dev, samp_rate);
  60. 	r = rtlsdr_set_center_freq(rtlsdr_dev, frequency);
  61.  
  62. 	if (0 == gain) {
  63.         /* Enable automatic gain */
  64.         r = rtlsdr_set_tuner_gain_mode(rtlsdr_dev, 0);
  65. 	} else {
  66. 		/* Enable manual gain */
  67. 		gain = nearest_gain(rtlsdr_dev, gain);
  68.         r = rtlsdr_set_tuner_gain_mode(rtlsdr_dev, 1);
  69.         r = rtlsdr_set_tuner_gain(rtlsdr_dev, gain);
  70. 	}
  71.  
  72. 	r = rtlsdr_set_freq_correction(rtlsdr_dev, ppm_error);
  73.  
  74.     while(1);
  75.     return 0;
  76. }

使用示波器抓取波形：