S5L8720 (Hardware)

This should help people reversing iBoot and friends. It is a work in progress.

DMA (PL080)

This appears to use an ARM PrimeCell PL080. You can read the technical reference manual here.

Base (dmac0): 0x38200000 Base (dmac1): 0x39900000
Register	Description
0x0	Interrupt Status
0x4	TC Status (If HIGH, transaction complete)
0x8	TC Interrupt Clear
0xC	Error Interrupt Status
0x10	Error Interrupt Clear
0x14	TC Interrupt Status Before Masking (Raw)
0x18	Error Interrupt Status Before Masking (Raw)
0x1C	DMA Channels Enabled
0x30	Controller Configuration
0x34	Enable / Disable Synchronization
0x100	Channel 0 Source Address
0x104	Channel 0 Destination Address
0x108	Channel 0 Linked List Address
0x10C	Channel 0 Control 1
0x110	Channel 0 Control 2
0x114	Channel 0 Configuration

VIC (PL192)

This appears to use an ARM PrimeCell PL192. You can read the technical reference manual here.

Register Table

Base (vic0): 0x38E00000 Base (vic1): 0x38E01000
Register	Description
0x0	IRQ Status
0x4	FIQ Status
0x8	Raw Interrupt Status
0xC	Interrupt Select (0=IRQ, 1=FIQ)
0x10	Interrupt Enable (0=Disabled, 1=Enabled)
0x14	Interrupt Enable Clear (Write-Only; 0=No Effect, 1=Interrupt enabled with previous reg disabled)
0x18	Software Interrupt (0=Disabled, 1=Enabled)
0x1C	Software Interrupt Clear (Write-Only; 0=No Effect, 1=Interrupt enabled with previous reg disabled)
0x20	Register Protection Mode. If bit 0 is set to 1, then Protection Mode is on and only privileged mode writes will work.
0x24	Software Interrupt Priority Mask (0=Masked, 1=Not Masked)
0x100	Vector Addresses
0x200	Vector Priority Levels
0xFE0 through 0xFEC	Peripheral Identification Registers
0xFF0 through 0xFFC	PrimeCell Identification Registers Register 0xFF0: Should read as 0x0D Register 0xFF4: Should read as 0xF0 Register 0xFF8: Should read as 0x05 Register 0xFFC: Should read as 0xB1

Peripheral Identification Registers

The four registers 0xfe0, 0xfe4, 0xfe8, and 0xfec, are four "8-bit registers that can be conceptually treated as one 32-bit register" according to the technical reference manual. Here are some explanations about these registers if you don't feel like digging through the reference manual. If you do, read pages 64 through 66.

Values for the S5L8720

0x38e00fe0: 00000092
0x38e00fe4: 00000011
0x38e00fe8: 00000004
0x38e00fec: 00000000

Part Number

Bits 7 through 0 of register 0xfe0 is one portion of the part number (0x92), then bits 3 through 0 of register 0xfe4 is the other portion of it (0x1). If you do some annoying shifting, to put it together, you get 0x192 (0x92|0x11<<8&0xFFF==0x192). 0x192 indicates that it is an ARM PrimeCell PL192.

Designer

Bits 7 through 4 of register 0xfe4 is one portion of the designer tag (0x1), then bits 3 through 0 of register 0xfe8 is the other portion of it (0x4). Like above, we can do (0x11 | 0x4<<4) and we get 0x41, which is "A" in ASCII, meaning it was designed by ARM Limited.

Revision Number

Unlike the above two, this one is pretty easy. Bits 7 through 4 of register 0xfe8 is the revision number, which is "0" at least for the iPod touch 2G.

Configuration

The reference manual simply states that bits 7 through 2 should read back as 0, and nothing more about them. It also states that bits 1 through 0 indicate the number of interrupts supported, which appear to be 32 for the iPod touch 2G (0b00=32 Supported, 0b01=64 Supported, 0b10=128 Supported, 0b11=256 Supported).

CHIPID

All information here was gathered by reversing iBoot and friends.

Base: 0x3D100000
Register	Description
0x0	Unused & Unreferenced Register
0x4	Not yet documented
0x8	Chip Info Chip ID: Bits 31 through 16 (0x8720, meaning it is an S5L8720) SCEP: Bits 15 through 1 (0x01)

WDT (Watchdog Timer)

Base: 0x3C800000
Register	Description
0x0	Control Register NOTE: It seems that you can disable Watchdog Timer by rewriting this register to 0x00000000, and you can reboot the device by rewriting it to 0x100000
0x4	Watchdog Timeout Duration
0xC	Interrupt Clear

ARM7 (Second CPU)

All information here was gathered by looking at the code for the ARM7 Go command, as well as noticing the 0x38000000==0xb8000000 alias that the S5L8720 seems to have.

Base: 0x38600000
Register	Description
0x100	Running Status To halt the ARM7: Write 0x0 then 0x10 to this register To make it resume: Write 0x1 to this register
0x110	Code Address To run code, halt the ARM7, write the load address of the code to this register, write 0x3FF0000 to register 0x114, then resume the ARM7
0x114	"Code Waiting" I don't know exactly what this register does, but I named it like this because 0x3FF0000 is written to this register when there is a load address of code to be jumped to in register 0x110

UART

Base (uart0): 0x3CC00000 Base (uart1): 0x3DB00000 Base (uart2): 0x3DC00000 Base (uart3): 0x3DD00000
Register	Description

Links

• OpeniBoot
• Decoded iPod touch 2G DevTree