Summary of GPIO usage.

Introduction

Mapping the GPIO usage is usually a tought task. In the A320 we have had help from the fact that:

• You can make programs for the original firmware using the provided SDK.
• The OS does not use the MMU to protect the special registers, so you can write a program that can read the state of every register (and even change it).

Having a "known good" set of values for certain registers helped a lot setting up the linux kernel for the A320.

General information about GPIO on the JZ4740

The JZ4740 has four 32 bit GPIO ports. Each port is controlled by eight registers:

• PXPIN: state of the pin (read only).
• PXDAT: output value.
• PXIM: interrupt mask (1=mask interrupt).
• PXPE: pull resistor control (1=disable).
• PXFUN: function control (0=GPIO/interrupt, 1=special function).
• PXSEL: function select (0=GPIO/special function 0, 1=interrupt/special function 1).
• PXDIR: pin direction (0=input/low level int/falling edge int, 1=output/high level int/raising edge int).
• PXTRG: trigger selection (0=level trigger, 1=edge trigger).
• PXFLG: interrupt flag.

For PXDAT, PXIM, PXPE, PXFUN, PXSEL, PXDIR and PXTRG there are corresponding "set" and "clear" registers. For PXFLG there is only a "clear" register.

For example, if you want to set some bits of PXDAT, you must write a value with those bits set to PXDATS. If you want to clear some bits, you must write a value with those bits set to PXDATC.

Port A

This por is entirely used for SDRAM. These are the values read by an application running on the original firmware.

| PXDAT | 0x00000000 | 0000 0000 0000 0000 0000 0000 0000 0000 | |:------|:-----------|:----------------------------------------| | PXIM | 0xFFFFFFFF | 1111 1111 1111 1111 1111 1111 1111 1111 | | PXPE | 0x000000FF | 0000 0000 0000 0000 0000 0000 1111 1111 | | PXFUN | 0xFFFFFFFF | 1111 1111 1111 1111 1111 1111 1111 1111 | | PXSEL | 0x00000000 | 0000 0000 0000 0000 0000 0000 0000 0000 | | PXDIR | 0x00000000 | 0000 0000 0000 0000 0000 0000 0000 0000 | | PXTRG | 0x00000000 | 0000 0000 0000 0000 0000 0000 0000 0000 |

Port B

Most of this port is also used for SDRAM.

| PXDAT | 0x00040000 | 0000 0000 0000 0100 0000 0000 0000 0000 | |:------|:-----------|:----------------------------------------| | PXIM | 0xDFFFFFFF | 1101 1111 1111 1111 1111 1111 1111 1111 | | PXPE | 0x02418000 | 0000 0010 0100 0001 1000 0000 0000 0000 | | PXFUN | 0x9FF9FFFF | 1001 1111 1111 1001 1111 1111 1111 1111 | | PXSEL | 0x20000000 | 0010 0000 0000 0000 0000 0000 0000 0000 | | PXDIR | 0x20000000 | 0010 0000 0000 0000 0000 0000 0000 0000 | | PXTRG | 0x20000000 | 0010 0000 0000 0000 0000 0000 0000 0000 |

| 0 | SDRAM A0 | |:---|:---------| | 1 | SDRAM A1 | | 2 | SDRAM A2 | | 3 | SDRAM A3 | | 4 | SDRAM A4 | | 5 | SDRAM A5 | | 6 | SDRAM A6 | | 7 | SDRAM A7 | | 8 | SDRAM A8 | | 9 | SDRAM A9 | | 10 | SDRAM A10 | | 11 | SDRAM A11 | | 12 | SDRAM A12 | | 13 | SDRAM A13 | | 14 | SDRAM A14 | | 15 | NAND CL | | 16 | NAND AL | | 17 | GPIO output CS# signal to LCD | | 18 | GPIO output RESET# signal to LCD | | 19 | SDRAM DCS# | | 20 | SDRAM RAS# | | 21 | SDRAM CAS# | | 22 | SDRAM RDWE#/BUFD# | | 23 | SDRAM CKE | | 24 | SDRAM CK0 | | 25 | NAND CS1# | | 26 | NAND CS2# | | 27 | NAND CS3# | | 28 | NAND CS4# | | 29 | GPIO input card detection (1=inserted) | | 30 | GPIO input battery charge status (0=charging, 1=charge finished) | | 31 | SDRAM WE0# |

Port C

Most of this port is used for LCD/TV out.

| PXDAT | 0x00280000 | 0000 0000 0010 1000 0000 0000 0000 0000 | |:------|:-----------|:----------------------------------------| | PXIM | 0x7FFDFFFF | 0111 1111 1111 1101 1111 1111 1111 1111 | | PXPE | 0x703CFFFF | 0111 0000 0011 1100 1111 1111 1111 1111 | | PXFUN | 0x3714FFFF | 0011 0111 0001 0100 1111 1111 1111 1111 | | PXSEL | 0x00020000 | 0000 0000 0000 0010 0000 0000 0000 0000 | | PXDIR | 0x08280000 | 0000 1000 0010 1000 0000 0000 0000 0000 | | PXTRG | 0x00020000 | 0000 0000 0000 0010 0000 0000 0000 0000 |

Pin usage:

| 0 | LCD D0 | |:---|:-------| | 1 | LCD D1 | | 2 | LCD D2 | | 3 | LCD D3 | | 4 | LCD D4 | | 5 | LCD_D5 | | 6 | LCD_D6 | | 7 | LCD_D7 | | 8 | LCD_D8 | | 9 | LCD_D9 | | 10 | LCD_D10 | | 11 | LCD_D11 | | 12 | LCD_D12 | | 13 | LCD_D13 | | 14 | LCD_D14 | | 15 | LCD_D15 | | 16 | GPIO input unused | | 17 | GPIO input START button | | 18 | LCD PCLK (not connected to LCD, connected to CH7024 XCLK input) | | 19 | GPIO output RS# signal to LCD | | 20 | LCD VSYNC (connected to LCD WR# signal) | | 21 | GPIO output=1, connected to CH7024 LCD_DE signal, used when in TV out mode, GPIO output=1 to keep the CH7024 disabled when not in TV out mode) | | 22 | GPIO input unused | | 23 | GPIO input unused | | 24 | SDRAM WE1# | | 25 | SDRAM WE2# | | 26 | SDRAM WE3# | | 27 | GPIO output internal speakers audio amplifiers shutdown (0=no sound) | | 28 | NAND FRE# | | 29 | NAND FWE# | | 30 | GPIO input, connected to NAND read/busy signal | | 31 | There is not a PC31 pin, this is used to select between JTAG and UART functions, which share the same set of pins. PXSEL=1 selects UART |

Port D

| PXDAT | 0x80100098 | 1000 0000 0001 0000 0000 0000 1001 1000 | |:------|:-----------|:----------------------------------------| | PXIM | 0xC7B13F98 | 1100 0111 1011 0001 0011 1111 1001 1000 | | PXPE | 0xF1A02100 | 1111 0001 1010 0000 0010 0001 0000 0000 | | PXFUN | 0x27803F00 | 0010 0111 1000 0000 0011 1111 0000 0000 | | PXSEL | 0x3FCEC067 | 0011 1111 1100 1110 1100 0000 0110 0111 | | PXDIR | 0xC0300090 | 1100 0011 0000 0000 0000 0000 1001 0000 | | PXTRG | 0x384EC067 | 0011 1000 0100 1110 1100 0000 0110 0111 |

| 0 | GPIO input A button | |:---|:------------------------| | 1 | GPIO input B button | | 2 | GPIO input Y button | | 3 | GPIO input, unused but tied to a test point according to schematic | | 4 | GPIO output=1, unused but tied to a test point according to schematic | | 5 | GPIO input DPAD LEFT | | 6 | GPIO input DPAD UP | | 7 | GPIO output=1, earphones audio MUTE control (0=mute, though actually just makes the sound bad) | | 8 | miniSD CMD | | 9 | miniSD CLK | | 10 | miniSD D0 | | 11 | miniSD D1 | | 12 | miniSD D2 | | 13 | miniSD D3 | | 14 | GPIO input LEFT SHOULDER button | | 15 | GPIO input RIGHT SHOULDER button | | 16 | GPIO input, unused according to schematic (but seems that there's an external driver present because readback fails if configured as output) | | 17 | GPIO input SELECT button | | 18 | GPIO input DPAD RIGHT | | 19 | GPIO input X button | | 20 | GPIO output=1, battery charge control (1=enable) (grounds a resistor which controls the charge current, note that this pin is also SSI data output and thus with some work could be used as a PWM output to control charge current) | | 21 | GPIO output=0, connectedto the mistery W35 chip | | 22 | GPIO input HOLD position of power slider | | 23 | I2C SDA, connected to TV and FM chips | | 24 | I2C SCK, connected to TV and FM chips | | 25 | UART0 TXD, serial console | | 26 | UART0 RXD, serial console | | 27 | GPIO input DPAD DOWN | | 28 | GPIO input USB power detection (1=power present) | | 29 | POWER BUTTON, but FUN=1 (jz4740.h says this pin does not have special function, but seems to be wrong since it's clearly WAKE_UP) | | 30 | GPIO output=0, though depicted in the schematic as input from the mistery W35 chip | | 31 | GPIO output LCD backlight (1=max, use as PWM7 to obtain different levels) |