I just realized that for this API, txLen + rxLen must be <= 14. Split your transaction into two reads. The other thing you may have to do is to put the SF out of deep sleep before reading and then put it back in deep sleep after you are done. Since you are bypassing the serial flash driver, you have to request the SF driver to do it for you. Here is some pseudocode:
extern void sfi_exitDeepPowerDown(void);
extern void sfi_enterDeepPowerDown(void);
extern void spiffy_txrxBlock(UINT32 txLen, const UINT8* txBuf, UINT32 rxLen, UINT8* rxBuf, void* ctxt);
UINT8 txBuf[5] = {0x5A, 0x11, 0x22, 0x33, 0x00}; /// instruction, 3 byte address, dummy byte
UINT8 rxBuf[12];
// Bring the SF out of deep sleep first
sfi_exitDeepPowerDown();
// Read keep rx + tx <= 14
spiffy_txrxBlock(5, txBuf, 9, rxBuf, (void*)spiffy_cfg_adr);
// --> Update address to read here.
spiffy_txrxBlock(5, txBuf, 3, rxBuf + 9, (void*)spiffy_cfg_adr);
// Put the SF back in deep sleep.
sfi_enterDeepPowerDown();
