AVR102 Block Copy Routines

AVR102: Block Copy Routines
Features
• Program Memory (Flash) to SRAM Copy Routine
• SRAM to SRAM Copy Routine
• Extremely Code Efficient Routines
Flash → SRAM: 6 Words,
SRAM → SRAM: 5 Words
• Runable Test/Example Program
Introduction
8-bit
Microcontroller
Application
Note
This application note contains routines for transfer of data blocks.
•
Flash to SRAM Copy. Copies data blocks of sizes up to 256 bytes from any Flash
address to any SRAM address.
•
SRAM to SRAM copy. Copies data blocks of sizes up to 256 bytes from any
SRAM source address to any SRAM destination address.
The routines are described in detail in the following sections.
Flash to SRAM Copy – Subroutine “flash2ram”
Before calling this routine, the following input parameters must be set up by the user:
•
“flashsize” – Register variable holding the size of the data block.
•
Z-pointer – 2 x source address of first Flash block byte.
•
Y-pointer – Destination address of first SRAM block byte.
The routine uses the “LPM”-instruction which is the one to use for data transfer from
Flash to Register File. The instruction selects the Flash word (16-bit) pointed to by the
15 most significant bytes of the Z-pointer. If LSB of the Z-pointer is 0, the lower byte of
the Flash word is returned, otherwise the higher byte is returned. The returned byte is
always found in R0. To obtain the 15 MSBs of Z with the correct word value, the user
must be careful to load Z with two times the address of the first double byte in the
table. The program listing shows how to handle this precaution.
During data transfer, the auto-increment facility of the pointers is utilized. Writing to
SRAM is done using the “ST Y+,Rs”-instruction. The “LPM”-instruction does not support auto-increment or decrement. The “ADIW” instruction is used to increment the 16bit pointer.
The register variable “flashsize” is used as a loop counter in the routine.
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1
Figure 1. “flash2ram” Flow Chart
FLASH2RAM
R0 ← [email protected] (LPM)
[email protected] ← R0,
Y←Y+1
Z←Z+1
FLASHSIZE ← FLASHSIZE - 1
N
FLASHSIZE = 0?
Y
RETURN
Table 1. “flash2ram” Register Usage
Register
Input
Internal
R0
Output
Temporary data storage
R16
“flashsize” – Size of data block to copy
R28
“YL” – Low address of SRAM data start
R29
“YH” – High address of SRAM data start
R30
“ZL” – Low address of Flash data start
R31
“ZH” – High address of Flash data start
Table 2. “flash2ram” Performance Figures
Parameter
Value
Code Size (Words)
5 + return
Execution Time
10 x (block size) + return
Register Usage
2
Low Registers
High Registers
Pointers
Interrupts Usage
None
Peripherals Usage
None
:1
:1
:Y, Z
AVR102
0933B–AVR–05/02
AVR102
SRAM to SRAM
Copy –
Subroutine
“ram2ram”
Before calling this routine, the following input parameters must be set up by the user:
•
“ramsize” – Register variable holding the size of the data block.
•
Z-pointer – source address of first byte in block.
•
Y-pointer – destination address of first byte in block.
By utilizing the pointer auto-increment facility, this routine is extremely compact. Moving one
byte of data and incrementing both pointers requires two instructions only. Two more instructions are needed to decrement an check the register variable “ramsize” which is used as a
loop counter in the routine. The data are temporarily stored in the register variable “ramtemp”
during transfer.
Figure 2. “ram2ram” Flow Chart
RAM2RAM
RAMTEMP ← [email protected],
Z←Z+1
[email protected] ← RAMTEMP,
Y←Y+1
RAMSIZE ← RAMSIZE - 1
RAMSIZE = 0?
N
Y
RETURN
Table 3. “ram2ram” Register Usage
Register
Input
R1
Internal
Output
“ramtemp” – Temporary data storage
R16
“ramsize” – Size of data block to copy
R28
“YL” – Destination address low byte
R29
“YH” – Destination address high byte
R30
“ZL” – Source address low byte
R31
“ZH” – Source address high byte
3
0933B–AVR–05/02
Table 4. “flash2ram” Performance Figures
Parameter
Value
Code Size (Words)
4 + return
Execution Time
6 x (block size) + return
Register Usage
Test/Example
Program
4
Low Registers
High Registers
Pointers
Interrupts Usage
None
Peripheral Usage
None
:1
:1
:Y, Z
The application note program file contains a runable test program which uses the copy application routines to copy 20 bytes of data from Flash to SRAM, then make a second copy of the
data at another SRAM location. The test program is made for use with an AT90S8515. By
changing including another “*def.inc” file, the program can be used with any other AVR MCU
with SRAM.
AVR102
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AVR102
5
0933B–AVR–05/02
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0933B–AVR–05/02
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