Rainbow Electronics ATR0621 - Manual (Page 4)

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4890AS–GPS–09/05
ATR0621 [Preliminary]
2. Architectural Overview
2.1 Description
The ATR0621 architecture consists of two main buses, the Advanced System Bus (ASB) and
the Advanced Peripheral Bus (APB). The ASB is designed for maximum performance. It inter-
faces the processor with the on-chip 32-bit memories and the external memories and devices
by means of the External Bus Interface (EBI). The APB is designed for accesses to on-chip
peripherals and is optimized for low power consumption. The AMBA Bridge provides an inter-
face between the ASB and the APB.
An on-chip Peripheral Data Controller (PDC2) transfers data between the on-chip
USARTs/SPI and the on-chip and off-chip memories without processor intervention. Most
importantly, the PDC2 removes the processor interrupt handling overhead and significantly
reduces the number of clock cycles required for a data transfer. It can transfer up to 64K con-
tiguous bytes without reprogramming the starting address. As a result, the performance of the
microcontroller is increased and the power consumption reduced.
The ATR0621 peripherals are designed to be easily programmable with a minimum number of
instructions. Each peripheral has a 16 Kbyte address space allocated in the upper 3 Mbyte of
the 4 Gbyte address space. (Except for the interrupt controller, which has 4 Kbyte address
space.) The peripheral base address is the lowest address of its memory space. The periph-
eral register set is composed of control, mode, data, status, and interrupt registers.
To maximize the efficiency of bit manipulation, frequently written registers are mapped into
three memory locations. The first address is used to set the individual register bits, the second
resets the bits, and the third address reads the value stored in the register. A bit can be set or
reset by writing a “1” to the corresponding position at the appropriate address. Writing a “0”
has no effect. Individual bits can thus be modified without having to use costly read-modify-
write and complex bit-manipulation instructions.
All of the external signals of the on-chip peripherals are under the control of the Parallel I/O
(PIO2) Controller. The PIO2 Controller can be programmed to insert an input filter on each pin
or generate an interrupt on a signal change. After reset, the user must carefully program the
PIO2 Controller in order to define which peripheral signals are connected with off-chip logic.
The ARM7TDMI ® processor operates in little-endian mode on the ATR0621 GPS Baseband.
The processor's internal architecture and the ARM ® and Thumb ® instruction sets are
described in the ARM7TDMI datasheet. The memory map and the on-chip peripherals are
described in detail in the ATR0621 full datasheet. The electrical and mechanical characteris-
tics are also documented in the ATR0621 full datasheet.
The ARM standard In-Circuit Emulation debug interface is supported via the JTAG/ICE port of
the ATR0621.
Features of the ROM firmware are described in software documentation available from u-blox
AG.