How does the DSP chip select the external clock?

How does a DSP chip select an external clock?
The internal instruction cycle of a DSP is relatively high, and the main frequency of an external crystal oscillator is not enough, so most DSP chips have PLLs inside. But each series is different.
1) TMS320C2000 series:
TMS320C20x: PLL can be divided by 2, ×1, ×2 and ×4, so the external clock can be 5MHz-40MHz
. TMS320F240: PLL can be divided by 2, ×1, ×1.5, ×2, ×2.5, ×3, ×4, ×4.5, ×5 and ×9, so the external clock can be 2.22MHz-40MHz.
TMS320F241/C242/F243: PLL can be ×4, so the external clock is 5MHz. TMS320LF24xx: PLL can be adjusted by RC, so the external clock is 4MHz-20MHz. TMS320LF24xxA:
PLL can be adjusted by RC, so the external clock is 4MHz-20MHz.
2)TMS320C3x series:
TMS320C3x: No PLL, so the external main frequency is twice the operating frequency.
TMS320VC33: PLL can be ÷2, ×1, ×5, so the external main frequency can be 12MHz-100MHz.
3)TMS320C5000 series:
TMS320VC54xx: PLL can be ÷4, ÷2, ×1-32, so the external main frequency can be 0.625MHz-50MHz. TMS320VC55xx: PLL can be ÷4, ÷2, ×1-32, so the
external main frequency can be 6.25MHz-300MHz.
4)TMS320C6000 series:
TMS320C62xx: PLL can be ×1, ×4, ×6, ×7, ×8, ×9, ×10 and ×11, so the external main frequency can be 11.8MHz-300MHz.
TMS320C67xx: PLL can be ×1 and ×4, so the external main frequency can be 12.5MHz-230MHz.
TMS320C64xx: PLL can be ×1, ×6 and ×12, so the external main frequency can be 30MHz-720MHz