Cansat
/
SPIFlash_LowPowerLab
2
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Updated Comments about sleep() 

Clarification that after using sleep(), wake() must be the first function used to communicate with the flash chip.
If this isn't the case, a noisy MISO line can cause the code to hang in the while(busy) loop in the command() function.
This is a "fix" for "gitHub bug #26".
This commit is contained in:
JasonC0x0D 2021-06-07 20:07:28 -07:00 committed by GitHub
parent 6423a585c4
commit ac7bc9a993
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 16 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
SPIFlash.cpp
View File

@ -38,8 +38,15 @@ uint8_t SPIFlash::UNIQUEID[8];
/// IMPORTANT: NAND FLASH memory requires erase before write, because /// IMPORTANT: NAND FLASH memory requires erase before write, because
/// it can only transition from 1s to 0s and only the erase command can reset all 0s to 1s /// it can only transition from 1s to 0s and only the erase command can reset all 0s to 1s
/// See http://en.wikipedia.org/wiki/Flash_memory /// See http://en.wikipedia.org/wiki/Flash_memory
/// The smallest range that can be erased is a sector (4K, 32K, 64K); there is also a chip erase command /// The smallest range that can be erased is a sector (4K, 32K, 64K); there is also a chip erase command
/// IMPORTANT: When flash chip is powered down, aka sleeping, the only command it will respond to is
/// Release Power-down / Device ID (ABh), per section 8.2.19 of the W25X40CL datasheet.
/// This means after using the sleep() function of this library, wake() must be the first
/// function called. If other commands are used, the flash chip will ignore the commands.
/// The risk is that the code can hang if there is noise/static on the MISO line,
/// specifically noise/static that would evaluate to HIGH or 1.
/// Constructor. JedecID is optional but recommended, since this will ensure that the device is present and has a valid response /// Constructor. JedecID is optional but recommended, since this will ensure that the device is present and has a valid response
/// get this from the datasheet of your flash chip /// get this from the datasheet of your flash chip
@ -180,11 +187,14 @@ void SPIFlash::command(uint8_t cmd, boolean isWrite){
command(SPIFLASH_WRITEENABLE); // Write Enable command(SPIFLASH_WRITEENABLE); // Write Enable
unselect(); unselect();
} }
//wait for any write/erase to complete // wait for any write/erase to complete
// a time limit cannot really be added here without it being a very large safe limit // a time limit cannot really be added here without it being a very large safe limit
// that is because some chips can take several seconds to carry out a chip erase or other similar multi block or entire-chip operations // that is because some chips can take several seconds to carry out a chip erase or other similar multi block or entire-chip operations
// a recommended alternative to such situations where chip can be or not be present is to add a 10k or similar weak pulldown on the //
// open drain MISO input which can read noise/static and hence return a non 0 status byte, causing the while() to hang when a flash chip is not present // Note: If the MISO line is high, busy() will return true.
// This can be a problem and cause the code to hang when there is noise/static on MISO data line when:
// 1) There is no flash chip connected
// 2) The flash chip connected is powered down, aka sleeping.
if (cmd != SPIFLASH_WAKE) while(busy()); if (cmd != SPIFLASH_WAKE) while(busy());
select(); select();
SPI.transfer(cmd); SPI.transfer(cmd);