Hello,
My notes on "requiring" (or strongly recommending) separate storage.
A couple of times we have gone around the issue of "is it reasonable to
require new platforms have separate storage for firmware".
Pros:
P1) No disk partition plan etc
P2) Runtime var storage is much easier
Cons:
C1) Cost
C2) Boot speed
C3) Board becomes "state full" and brick-able
C4) Need Buy-in from board makers
I hope we understand the pros so I won't go deep on those.
WRT C1 & C2: Cost & boot speed
Pocket Beagle ($25) has a 2Kx8 I2C EEPROM built into the SIP (system in
package). This allows a single binary SPL to boot from uSD on multiple
boards (PocketBeagle BBW, BBB, BBBlue, TI EVM, etc) as the EEPROM has
board ID info.
I looked for other low cost boards with dedicated firmware storage.
PINE A64-LTS ($32) and SOPINE ($30) have 16MB of SPI flash.
The original PINE A64 ($15) has no on board storage.
Are there other boards I should look at?
What would this look like if we put:
* SPL & vars only into SPI flash
* SPL & U-boot & vars into SPI flash
* SPL/U-boot or EDK2 + vars into QSPI
I assume 64KB for SPL, <500KB for SPL+Uboot, and 1MB for EDK2.
QSPI:
1MB $0.67
2MB $0.70
16MB $1.62 (PINE A64-LTS)
133MHz == 66MB/s
U-boot, 500KB in 7ms
EDK2, 1MB in 14ms
SPI:
128KB $0.28
1MB $0.33
104Mhz == 13MB/s
SPL only, 64KB in 5ms
U-boot, 500KB in 38ms
I2C:
ID only 256x8 $0.09
BBB etc 4Kx8 $0.13
32bytes @100KHz = 2.5ms
Note that on PocketBeagle the I2C cost is already baked into the SIP so
you can't subtract this cost from the cost of the SPI flash. This is a
legacy issue but does so that buy-in takes time to filter down.
Would a future SIP include an SPI flash? If you do then you need to fix
how big.
WRT C3: State-full and brickable
As long as the SOC supports multiple bootmodes and the board adds a
button or switch to select a recovery mode, this can be handled.
BeagleBone black boots from eMMC (which is brickable) but holding a
button at power up causes it to ignore everything in eMMC and boot form
uSD. The uSD in this recovery mode need not be EBBR compliant (but I
would like to allow it to be.)
PocketBeagle like board would need to add a jumper or similar.
C4: Board maker buy-in
Probably the biggest barrier. Must show value of EBBR on legacy boards
before people see the value. But if legacy works OK then why change?
Bill
----------------
William A. Mills
Chief Technologist, Open Solutions, SDO
Texas Instruments, Inc.
20450 Century Blvd
Germantown MD 20878
240-643-0836
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