Browse Prior Art Database

A Method for RAM Bit Access Via Memory Remapping

IP.com Disclosure Number: IPCOM000235700D
Publication Date: 2014-Mar-20
Document File: 3 page(s) / 53K

Publishing Venue

The IP.com Prior Art Database

Abstract

Some low tie MCUs do not have bit access instructions. Such instructions are useful in software as flag access in process control. In most applications, the bit Boolean operation can take up to 20~30% in low tie MCU. And software has to implement such feature by splitting bit Boolean operations into read-change-writeback and can’t be atomic access. This results in more execution time and code space. In this paper we propose a method for RAM bit access implemented with a memory remapping, utilize bit write enable of a RAM and some decode/extract logic to achieve bit atomic access in RAM.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

A Method for RAM Bit Access Via Memory Remapping

 Abstract

Some low tie MCUs do not have bit access instructions.  Such instructions are useful in software as flag access in process control.  In most applications, the bit Boolean operation can take up to 20~30% in low tie MCU.  And software has to implement such feature by splitting bit Boolean operations into read-change-writeback and can’t be atomic access. This results in more execution time and code space.  In this paper we propose a method for RAM bit access implemented with a memory remapping, utilize bit write enable of a RAM and some decode/extract logic to achieve bit atomic access in RAM.

Introduction

 The bit access operation is a basic element of applications in MCU.  If the MCU doesn’t have bit access instructions, there are several ways to achieve it.

·         Implement some register bits mapped to peripherals memory map. This method costs gate counts with less flexible in use.

·         Implement some logic like ARM CM4, to embed bit-band support, using read-change-writeback operation, always incur two RAM accesses.

·         Using whole byte of RAM as one flag, this is un-acceptable in SOC with small RAM size.

The method we have is using a memory remapping, RAM bit write enable and some logic. It can cover full RAM space with lower cost of gate count.

·         Define an alias bit-band region (memory remapping), See Figure 1. In low end MCU, we have much reserved the memory space that can be used as bit-band region. We can define one byte or one word memory address for a single RAM bit. With the bit-band region definition, we can use extra address line to decode which bit is accessed in RAM.

·         Logic design for RAM bit write access is using address line to decode and toggle the RAM bit write enable and shift the LSB of write data correspondingly. And for RAM bit read access, decode the address line and shift the corresponding RAM data to LSB of read data...